Male horn dimorphism, phylogeny and systematics of rhinoceros ...

CSIRO PUBLISHING 

www.publish.csiro.au/journals/ajz Australian Journal of Zoology, 2003, 51, 213–258 

Male horn dimorphism, phylogeny and 

systematics of rhinoceros beetles of the genus 

Xylotrupes (Scarabaeidae:Coleoptera) 

J. Mark Rowland 

Department of Biology, University of New Mexico, Albuquerque, 

New Mexico 87131, USA. Email: rowland@unm.edu 

Abstract 

Male horns in several groups of beetles represent a special class of secondary sexual characters in which 

condition-dependent, alternate developmental programs produce not only a bimodal horn-size distribution, 

but also discrete male mating behaviours correlated with these alternate phenotypes. While these 

intrasexual dimorphisms have recently received theoretical and experimental attention concerning how they 

are produced and modified, less has been focussed on the macroevolutionary behaviour of the ontogenetic 

mechanism that produces them. The developmental program that produces alternate male morphologies is 

manifested by a non-linear horn-size allometry that has been noted to vary within and among various taxa 

according to its shape and position. The purpose of the present study is to produce a preliminary measure 

of the macroevolutionary behaviour of these allometric characters as a function of defined phylogenetic 

scale among the rhinoceros beetles of the widespread genus Xylotrupes. 

A phylogenetic analysis performed herein suggests that Xylotrupes is monophyletic and is composed of 

six lineages, which are treated as discrete species. The taxon Xylotrupes gideon of previous literature is 

shown to constitute five species. Explicit rationale, including morphological diagnoses and evidence of 

reproductive isolation, supports a new, readily testable taxonomic scheme that recognises the following 

species: Xylotrupes florensis in the Lesser Sunda and Tanimbar Islands, Indonesia; X. meridionalis in Sri 

Lanka and India; X. ulysses in Sulawesi, Moluccas, Australia, Papua New Guinea and Melanesia; X. 

pubescens in the Philippines, Sumatra and Sulawesi; X. mniszechi in south-central and south-east Asia and 

China; and X. gideon in west Malaysia, Borneo and the Indonesian archipelago from Sumatra through the 

Lesser Sunda Islands. Subspecies are recognised in some of these taxa and are based upon geographic and 

phylogenetic partitioning. 

As in other groups of beetles, the sigmoidal allometric relationship of horn size to body size produces 

bimodal horn-size distributions in the males of all the species of Xylotrupes in which adequate samples were 

obtained. The present data show that there is more variation in allometric shape but less variation in 

allometric position in Xylotrupes than in dung beetles of the genus Onthophagus. Moreover, the 

phylogenetic patterns of variation in horn allometry among the taxa of Xylotrupes indicate that as much 

variation in allometric position and shape occurs among the subspecies of a single species, X. ulysses, as 

occurs among the remainder of the species in this genus. 

Evidence is provided that allometric position in Xylotrupes is responsive to interspecific competition 

inasmuch as character displacement of body size relative to horn size occurs in newly discerned sympatric 

populations of X. gideon and X. pubescens zideki. Further, major evolutionary modifications in allometric 

shape in two subspecies of X. ulysses have apparently occurred independently and involve fundamentally 

different adaptive mechanisms. 

These results suggest that modifications in the developmental program that controls male horn 

dimorphism are a principal feature of diversification in the beetles of the genus Xylotrupes. 

ZO02013 

Male J. M. Rowl hor n dimorphism a nd in Xylot rupes 

Introduction 

The males in many groups of beetles possess horns that are used as weapons in intrasexual 

competition, such as for reproductive access to females (Davis 1833; Wallace 1869; Beebe 

1944; Eberhard 1977, 1979, 1987; Palmer 1978). In some species, the dimensions of these 

ornaments covary with body size. In other species, a non-linear, often sigmoidal allometry 

© CSIRO 2003 10.1071/ ZO02013 0004-959X/03/030213

214 Aust. J. Zoology J. M. Rowland 

produces a bimodal horn-size distribution (Bateson and Brindley 1892; Bowden 1957; 

Eberhard 1982; Siva-Jothy 1987; Eberhard and Gutierrez 1991; Rasmussen 1994). This 

intrasexual dimorphism is a consequence of the capacity of the males to develop along 

either of two discrete ontogenetic pathways, the alternate expressions of which are 

regulated by an environmentally cued genetic switch that is sensitive to larval size 

(Eberhard 1982). Individuals above a critical body size metamorphose proportionally larger 

horns and display distinct behavioural traits compared with males of smaller body size. 

This developmental strategy minimises the frequency of males with intermediate horn sizes 

and mating behaviours, appears to selectively maximise the reproductive contribution of 

both ‘major’ and ‘minor’ males in these populations, and thus, in theory, enhances fitness 

of the genotype (Emlen 1996). 

Recent experimental work has focussed on this developmental mechanism as a model 

for investigating certain aspects of how secondary sexual characters evolve (Emlen 1994, 

1996; Moczek and Emlen 1999). One of these studies (Emlen 1996) demonstrates that 

position of the allometry along the body size axis in an Onthophagus dung beetle responds 

readily to directional artificial selection. It was also noted that sexual selection has 

apparently produced a broad range of such adaptive types among a suite of American 

species of that genus. In contrast, the sigmoidal allometric shape of the distribution did not 

change in response to artificial selection, nor was macroevolutionary change reflected by 

significant variation in allometric shape among these species of Onthophagus. Further, the 

latter studies provided the remarkable evidence that absolute horn morphology in these 

beetles possessed little heritable variation, but that the developmental mechanism 

regulating relative horn expression possessed significant heritable variation and thus had 

much more potential for rapid evolutionary change. However, the macroevolutionary 

patterns of variation in this developmental mechanism have been little explored among the 

Scarabaeidae, and data that will support comparative analyses thus are rare. 

It seems, moreover, that further taxon-based analysis of this developmental mechanism, 

especially as a function of phylogenetic scale, will yield rich evidence of its evolutionary 

behaviour as well as insights concerning the selective environments that produce relevant 

change. Xylotrupes gideon, for example, is thought to be one of the most widespread large 

dynastine beetles in the world, has a strongly bimodal horn-size distribution in the males of 

some populations (Bateson and Brindley 1892) and is distinctly less so in other populations 

(Allsopp 1991). This taxon has been reported from Sri Lanka, India, the Himalayan region, 

south-east Asia, China, the Philippines, the Malay Archipelago, Australia, Papua New 

Guinea, and into Melanesia as far as Vanuatu. In many of these regions Xylotrupes can be 

quite common and thus procured in sufficient numbers to produce robust delineation of 

geographic variation in allometric shape and position of the horn-size versus body-size 

distributions. 

Among several large samples of Xylotrupes procured for this purpose, the bivariate plot 

of a sample from Gunung Dempo, Bengkulu Province, Sumatra demonstrated two distinct, 

more-or-less parallel distributions of pronotal horn length versus pronotal width (Fig. 46). 

These distributions were found to coincide precisely with the presence or absence of a 

cephalic horn tooth (Fig. 1) and distinctive aspects of genital morphology (Figs 17, 26). 

This evidence indicates that two sympatric, reproductively isolated species of Xylotrupes 

occur on Gunung Dempo, Sumatra, in which a symmetrical character displacement of body 

size relative to horn size is manifest (Figs 2, 46). 

The discovery of sympatric species of Xylotrupes in which character displacement has 

occurred involving the developmental system producing male horn dimorphisms provides

Male horn dimorphism in Xylotrupes Aust. J. Zoology 215 

Fig. 1. Major males of X. gideon (above) and X. pubescens zideki (below) from Gunung Dempo, 

Bengkulu Province, Sumatra, where these species are sympatric. Males of these populations differ by the 

presence of a strong cephalic horn tooth in X. gideon and its absence in X. pubescens zideki. Scale = 2.25 

times life size. 

an important example of its evolutionary behaviour, but also raises further relevant 

questions. Documentation of the variations in the allometric parameters among populations 

of X. gideon requires determination of the actual diversity of taxa previously represented as 

that species. However, this presents an opportunity to compare macroevolutionary 

behaviour of this developmental system both within and among closely related taxa, and as 

a function of phylogenetic scale. 

Moreover, this report presents a phylogenetic analysis and a new systematic scheme for 

Xylotrupes that provide the framework for the principal objective of this investigation,


Fig. 2. Major and minor males of Xylotrupes gideon (left) and X. pubescens zideki (right) from Gunung 

Dempo, Bengkulu Province, Sumatra. Major males of the two species with the same pronotum + horn 

length and minor males of the two species with the same pronotum + horn length illustrate the 

displacement in body size where these species are sympatric. Scale = life size. 

which is the description and preliminary evaluation of the patterns of variations in horn 

dimorphism among its taxa. 

Systematics 

Xylotrupes is widespread in Australasia and the males of many populations are quite 

variable in adult morphology, especially in horn development. These circumstances have 

led to the introduction over 200 years of more than 30 competing species-group names. The 

most recent comprehensive taxonomic treatments of Xylotrupes (Endrödi 1951, 1976, 

1985) recognised two or three species and about 16 subspecies.


The first step in the present analysis was to determine whether the taxa recognised by 

Endrödi and the characters used to distinguish them would serve as a reliable basis for 

phylogenetic analysis. Samples procured from more than 50 localities representing a wide 

range of Australasian regions were examined for this purpose. To assess intrapopulational 

character variation, about 20 males were obtained from more than 20 localities. Study of 

this material has shown that almost all the morphological characters employed to 

discriminate taxa in the earlier principal taxonomic treatments of Xylotrupes (Schaufuss 

1885; Minck 1920; Endrödi 1951, 1976, 1985) are subject to considerable intrapopulational 

variation and thus are not useful for characterising and discriminating taxa. Among the 

traditional characters found to be of little or no practical use for identifying taxa on the basis 

of single specimens were colour, absolute horn size and shape, setation of the onychium and 

mentum, shape of the ocular canthus, punctation of the pronotum and elytra, and reticulation 

of the elytra. Of the previously employed characters, only the presence or absence of a 

cephalic horn tooth proved useful in characterising taxa and for phylogenetic analysis. 

In practice, the previous principal publications on Xylotrupes discriminated a great 

majority of its taxa largely on geographic rather than morphological grounds, which has 

resulted in a large number of inadequately defined taxa. Therefore, a comprehensive study 

was made of the present samples in order to identify new characters and terminal taxa 

suitable for the phylogenetic analysis. 

Examination of the male genitalia from dozens of diverse localities revealed that the 

raspulae of the internal sac segregate into several distinctive and discrete morphological 

types (Figs 4–30). These structures have been previously neglected as taxonomic characters 

in the Dynastini, but here provide the principal basis for establishing both the terminal taxa 

for the phylogenetic analysis and a new, readily testable taxonomic system for Xylotrupes. 

Recognition of the present taxa is based upon the following facts. In the present samples 

from more than 50 diverse localities that cover nearly the entire geographic range of 

Xylotrupes, there exist six discrete forms of the raspulae (Figs 4–30); these six taxa are 

diagnosable on the basis of unique combinations of raspular and other character states 

discussed below; most of these taxa are widely distributed and largely allopatric; and three 

pairs of these taxa, X. gideon and X. pubescens in Sumatra, X. gideon and X. florensis on 

Flores and Timor Islands, and X. pubescens and X. ulysses in Sulawesi, are sympatric but 

reproductively isolated. More explicit rationale for recognition of these taxa is presented in 

the ‘Species-group definitions’ below and in the Discussion. 

Species-group definitions and classifications 

Secondary sexual character displacement between sympatric populations of Xylotrupes, as 

in X. gideon and X. pubescens zideki (Fig. 46, Table 3), is a relevant and important example 

of the macroevolutionary behaviour of the developmental program that produces male horn 

dimorphism. It may also represent a significant feature in the diversification of this group. 

The dependence of such character displacement on reproductive isolation and the prospects 

of future studies of this phenomenon among the various populations of Xylotrupes suggest 

that the Biological Species Concept (BSC: Mayr 1963, 2000) might be most appropriate for 

definition and classification of its taxa. However, insufficient data are presently available 

concerning the reproductive propensities among some of these taxa to fully support the 

requirements of the BSC. On the other hand, since phylogenetic analysis provides the 

measure of macroevolutionary behaviour of the developmental mechanism, the 

Phylogenetic Species Concept (Rosen 1978; Nelson and Platnick 1981; Wheeler and 

Platnick 2000) might also justifiably serve to define these taxa. Due to the prevailing


confusion and complexities in making defensible use of either of these species concepts 

(see, for example, Wheeler and Meier 2000), I have not attempted to strictly conform to 

either. Instead, I present as much applicable information as possible concerning these taxa 

and leave it to subsequent users of this information to employ the species concept and 

classification that suits their particular purposes. 

The present classification is based on facts and inferences concerning reproductive 

compatibility, unique combinations of character states and phylogenetic relationships, and 

recognises subspecies. The latter device increases information concerning relationships in 

the formal nomenclature and is broadly used in the taxonomic literature on the Scarabaeidae. 

The use of the subspecies category conforms to the definition of O’Brien and Mayr (1991) 

inasmuch as these taxa are allopatric with respect to the other populations of the respective 

species and their descriptions recognise phylogenetic partitioning. Thus, by this mechanism 

it will be clear to future workers who desire to recognise phylogenetic species (e.g. sensu 

Wheeler and Platnick 2000) how the taxa of Xylotrupes might be so treated. 

The systematics section is constructed to achieve two principal objectives, a taxonomic 

revision of the genus Xylotrupes and the outcome of the phylogenetic analysis. The species 

accounts include descriptions of character states that are autapomorphic and/or diagnostic 

for each taxon; and those that are synapomorphic among groups of species. To more fully 

understand the characters used to discriminate the taxa, the reader should see the 

appropriate character descriptions [numbers in brackets] in the Phylogenetic Analysis, 

where they are described in detail. 

Abbreviations are as follows: Museum für Naturkunde der Humboldt Universität, Berlin 

(ZMHB); American Museum of Natural History, New York (AMNH); Museum National 

d’Histoire Naturelle, Paris (MNHN); Royal Ontario Museum, Ontario (ROM); Hungarian 

Natural History Museum, Budapest (HNHM); Natural History Museum, London (NHM); 

J. M. Rowland (JMR); New Mexico Museum of Natural History, Albuquerque (NMMNH); 

CSIRO, Canberra (CSIRO); Queensland Museum, Brisbane (QM); Museum of the 

Northern Territory, Darwin (MNT); Primary Industries and Fisheries, Darwin (PIF); 

University of Nebraska State Museum, Lincoln (UNSM); National Museum of Natural 

History, Washington DC (USNM); California Academy of Sciences, San Francisco (CAS). 

Genus Xylotrupes Hope 

Xylotrupes Hope 1837: 19; Burmeister 1847: 264; Lacordaire 1856: III, 446; Thomson 1859: 16; 

Schaufuss 1885: 191; Minck 1920: 216; Arrow 1910: 262; Endrödi 1951: 240; 1957: 64; 1976: 

225; 1985: 621; Silvestre 1997: 123. 

Endebius Lansberge 1880: 122 (syn. Arrow 1937: 38). 

Diagnosis 

Xylotrupes is one of 10 genera recognised by Endrödi (1985) in the tribe Dynastini, but is 

inadequately diagnosed in that work. This study, however, establishes that the only 

dynastine apomorph unique to Xylotrupes is the constitution of the right raspula [11] as a 

single large spine (Figs 4–30). Xylotrupes is also the only genus of this tribe with the 

following combinations of characters: both the pronotal and cephalic horns are apically 

bifurcate and the pronotal horn is about the same size as, or longer than, the cephalic horn 

in major males [1]. 

Type 

Scarabaeus gideon Linnaeus, 1767.


Distribution 

Sri Lanka, India, Pakistan, Nepal, China, Lanshu Island near Taiwan, south-east Asia, the 

Philippines, Malaysia, Indonesia, Australia, Papua New Guinea, and into Melanesia as far 

as Vanuatu. 

Xylotrupes florensis Lansberge 

(Figs 4, 32, 38, 43, 50; Table 2) 

Xylotrupes florensis Lansberge 1879: 153; Endrödi 1951: 242; 1976: 231; 1985: 622; Misunuma 1999: 

109. 

Endebius florensis: Lansberge 1880: 122. 

Diagnosis 

X. florensis is the only species without a left raspula [4], or a basal raspular piece [6] and 

with a single apical mandibular tooth [3]. Each of these states are considered plesiomorphic 

but represent possible reversals within the Dynastini. It is also the only species with a 

straight or non-reflected paramere blade [14] (Fig. 32), which is treated as 

symplesiomorphic with Trypoxylus dichotomus and the other taxa of Dynastini. The 

cephalic horn does not have a dorsal tooth. Autapomorphs include: comparatively small 

right raspular spine (Fig. 4); absence of an anterior pronotal suture; presence of acuminate 

cuticular projections basolateral to the pronotal horn; and acuminate basal tarsomere of leg 

III. At least some species of several dynastine genera, including Megasoma, but not 

Trypoxylus, possess an acuminate basal tarsomere of leg III. This acumination in 

X. florensis is thus an autapomorph relative to Trypoxylus and the other taxa of Xylotrupes, 

but possibly represents a reversal relative to other Dynastini. Females of X. florensis have a 

glossier dorsal integument than do other species of Xylotrupes, which is most evident on 

the pronotum. Horn size is strongly dimorphic and the allometry is strongly sigmoidal in 

populations of Flores Island (Fig. 50). 

Distribution 

Lesser Sunda Island from Flores Island to the Tanimbar Islands. 

Type data 

Flores Island, Indonesia. The type is said to be in St. Petersburg (Endrödi 1976). The 

identity of the type is not in question because the original description contains the following 

unmistakable character that is unique to this taxon: ‘Thorax cornu … basi intus utrinque biseu 

tridentato’. 

Specimens examined 

Indonesia: Flores Island, Tado lands, 45 km SE of Labuan Bajo, 36 males and 22 females 

(JMR); Flores Island, 3 males (ZMHB, JMR); Timor Island, 1 male (JMR), Adonarra, 

Wetar and Tanimbar Islands, 1 female each (ZMBH). 

Remarks 

Although only X. florensis had been previously reported from the Lesser Sunda Islands 

(Mizunuma 1999), I have also obtained males of X. gideon from both Flores and Timor 

Islands. Sympatric populations of these species are herein documented from near Labuan


Figs 3–6. Raspulae, left lateral view. 3, Trypoxylus dichotomus; 4, Xylotrupes florensis; 5, X. 

meridionalis from Kerala, India; 6, X. meridionalis from Sri Lanka. Scale bar = 3 mm. 

Bajo, Flores Island, which indicates that X. gideon and X. florensis are reproductively 

isolated. 

Xylotrupes meridionalis Prell 

(Figs 5, 6, 33, 39, 43; Table 2) 

Xylotrupes meridionalis Prell 1914: 216; Minck 1920: 217; Endrödi 1951: 241–242. 

X. meridionalis taprobanes Prell 1914: 217; Minck 1920: 217. 

X. gideon meridionalis: Endrödi 1957: 64, 65; 1976: 225. 

X. gideon socrates Endrödi 1985: 624. 

Diagnosis 

The elongate basal process of the right raspula in X. meridionalis (Figs 5, 6) originates on 

its lateral surface and does not serve as an articulation point for the left raspula, whereas in 

X. gideon the elongate basal process originates on the mesal surface and serves as an 

articulation point for the left raspula. Other autapomorphs in X. meridionalis include the 

unique proximal reflection of the base of the right raspula, and the large and widely 

divergent apical tines of the cephalic horn. The character and location of the conical 

protuberance that occurs apically at the base of the tines of the cephalic horn in X. 

meridionalis is distinct from the cephalic horn tooth [2] in X. mniszechi and X. gideon, and 

is considered convergent. Adequate samples were not available for description of horn 

allometry; however, the pronotal horn in major males is much shorter than in populations 

of Xylotrupes with strongly dimorphic horns.


Synapomorphs 

X. meridionalis is the sister taxon to the clade X. ulysses, X. pubescens, X. mniszechi and X. 

gideon, and shares with them the following apomorphs: two apical mandibular teeth [3], 

which perhaps represents a reversal relative to other Dynastini; presence of a basal raspular 

piece [6]; upward reflected parameral blades [14] (Figs 33–36); acuminate paraproct plates 

[16] and lateral location of the paraproct lobes [17] (Figs 39–42). 

Distribution 

Sri Lanka and southern India. 

Type data 

X. meridionalis: Madras, Schembaganur, India. X. meridionalis taprobanes: Kandy, Sri 

Lanka. Types are reportedly in ZMBH (Endrödi 1976), not examined. The identity of the 

type is not in question because the original description contains the following unmistakable 

character that is unique to this taxon: ‘Das Kopfhorn … in der Gabelungsstelle findet sich 

einer kleiner Höcker’. 


India: Madras, 2 males (NHM); Kerala, Pirmed, near Periyar, 2 males, 2 females (JMR); 

Bombay, 1 male (AMNH); ‘North India’, 1 male, 1 female (AMNH); Sri Lanka: 2 males 

(AMNH), 5 males (BMNH). 

Subspecies 

Prell (1914) distinguished X. meridonalis meridionalis and X. meridionalis taprobanes by 

more highly divergent apical tines of the cephalic horn in the latter, and by the form of the 

parameres. Too few specimens were available from Sri Lanka and southern India to yield 

conclusions concerning recognition of those subspecies. For reasons unclear to me, Endrödi 

(1976, 1985) treated the populations of Sri Lanka and southern India as X. gideon socrates. 

Xylotrupes ulysses (Guérin-Méneville) 

(Figs 7–14, 34, 35, 40, 43, 48, 49, 52; Tables 2, 4) 

Scarabaeus ulysses Guérin-Méneville 1830: 80. 

?Xylotrupes lorquini Schaufuss 1885: 192, 194. 

X. clinias Schaufuss 1885: 192; Minck 1920: 219; Endrödi 1951: 244. 

X. baumeisteri var. nicias Schaufuss 1885: 219. 

X. falcatus Minck 1920: 220; Endrödi 1951: 244. 

X. lamachus Minck 1920: 220. 

X. gideon ulysses: Endrödi 1951: 246, 247, 252; 1976: 231; 1985: 624. 

X. nicias Endrödi 1951: 244. 

X. gideon lorquini: Endrödi 1951: 246; 1976: 230; 1985: 624. 

X. gideon lamachus Endrödi 1951: 246; 1976: 230; 1985: 624. 

Diagnosis 

X. ulysses is the only species of Xylotrupes with the following combination of character 

states. The left and right raspular spines are similar in size (Figs 7–14) and the cephalic horn 

lacks a dorsal tooth. The paraprocts of the females in X. ulysses have a more strongly 

developed mesal interlocking blade and invagination [18] compared with other species


Figs 7–14. Raspulae, left lateral view. Xylotrupes ulysses. 7, X. ulysses ulysses; 8, X. ulysses australicus 

from Bundaberg, Queensland; 9, X. ulysses falcatus; 10, X. ulysses telemachos; 11–16: X. ulysses clinias: 

11, Sulawesi; 12, Wau Valley, Papua New Guinea; 13, Bougainville; 14, Vanuatu. Scale bar = 3 mm. 

(Figs 34, 35), which is autapomorphic, although females from New Ireland Province, Papua 

New Guinea, were not available for study. X. ulysses is the only taxon within Xylotrupes not 

yet identified by an autapomorphic character state in the raspular complex. There is more 

variation in raspular morphology and more diversity in horn allometry within X. ulysses


than within any of the other species. This variation is mostly explained by geography, and 

a subspecific classification is employed to recognise five subspecies on the basis of 

autapomorphs in four of them. 

Synapomorphs 

X. ulysses is the sister taxon to the clade comprising X. pubescens, X. mniszechi and 

X. gideon, and shares with them the following apomorphs: the paraproct plates are 

asymmetric [15], and possess a well developed interdigitating blade and invagination on the 

mesal surfaces [18] (Figs 40–42). 

Distribution 

Sulawesi and Sangi Island, east through the Molucca islands, Australia, Papua New Guinea, 

and Melanesia as far as Vanuatu. 

Type data 

See X. ulysses ulysses. 

Remarks 

The architecture of the right raspula below the process in X. ulysses ulysses, X. ulysses 

australicus, X. ulysses falcatus and X. ulysses telemachos, but not in X. ulysses clinias, is 

similar to, and may be homologous with, those features that form the cup-like structure [12] 

in X. pubescens, X. mniszechi and X. gideon. This suggests that X. ulysses might be 

paraphyletic (Fig. 43). 

X. lamachus Minck (1920) was described on the basis of two males from New Britain 

(‘Neu Pommern’) and a male from Papua New Guinea (ZMHB). The raspulae of two of 

these specimens are teratologically aberrant, leaving only one male from New Britain to 

compare to other taxa. This specimen is referable with certainty to X. ulysses and is most 

similar in raspular morphology to X. ulysses ulysses from Namatanai, New Ireland. 

However, until more specimens become available from this region it is uncertain whether 

X. lamachus should be treated as a synonym of the former taxon. 

X. lorquini Schaufuss (1885) was described on the basis of a single male from the 

Moluccas (ZMHB), but the specimens do not have the internal sac of the aedeagus 

preserved, thus its relationship to the other taxa is uncertain. The type locality and lack of 

a cephalic horn tooth suggests that it might be a member or ally of X. ulysses. The type 

specimen is a major male and is unique in possessing a distinctly longer cephalic horn 

relative to pronotal width and pronotal horn length compared with other males of 

Xylotrupes. 

Xylotrupes ulysses ulysses (Guérin-Méneville), stat. nov. 

(Figs 7, 43, 48, 52; Table 4) 

Scarabaeus ulysses Guérin-Méneville 1830: 80. 

Xylotrupes gideon ulysses: Endrödi 1951: 246, 247, 252; 1976: 231; 1985: 624. 

Diagnosis 

X. ulysses ulysses has a smaller basal process of the right raspula (Fig. 7) than does 

X. ulysses falcatus, but larger one than X. ulysses clinias; a more variable, and


hemispherical left raspular base than does X. ulysses australicus; a larger right raspular 

spine than does X. ulysses telemachos; and a much larger pronotal horn in relation to 

pronotal width in major males (Figs 48, 49) than does either X. ulysses australicus or X. 

ulysses telemachos. Horn size is strongly dimorphic and the allometry is strongly sigmoidal 

(Fig. 48). 

Distribution 

New Ireland Island, Papua New Guinea. 

Type data 

‘Port Praslin’ (former site about 5 km NNW of Cape St Georges), New Ireland. Location 

of the type is unknown (Endrödi 1976). I used specimens from within 100 km of the type 

locality to represent this taxon. 


Papua New Guinea: New Ireland Province, Namatanai, 35 males (JMR). Namatanai is 

approximately 100 km N of Port Praslin, and its populations are assumed to adequately 

represent those of the type locality. 

Xylotrupes ulysses clinias Schaufuss, comb. nov. 

(Figs 11–14, 35, 43, 48, 49; Table 4) 

Xylotrupes clinias Schaufuss 1885: 192, 194. 

?X. macleayi Montrouzier 1855: 19. 

X. baumeisteri var. nicias Schaufuss 1885: 192, 194. NEW SYNONYMY. 

X. trasybulus Minck 1920: 219, 220 (syn. Endrödi 1951: 244). 

X. asperulus Minck 1920: 220, 221. NEW SYNONYMY. 

X. gideon baumeisteri: Endrödi 1951: 244; 1985: 624. 

X. gideon clinias: Endrödi 1951: 246; 1985: 624. 

X. gideon asperulus: Endrödi 1951: 246; 1976: 231; 1985: 625; 

X. gideon szekessyi Endrödi 1951: 244; 1976: 231; 1985: 625. NEW SYNONYMY. 

Diagnosis 

The right raspula has a relatively smaller process, which is located closer to the base of the 

raspula, compared with the other subspecies of X. ulysses and with the other species of 

Xylotrupes (Figs 11–14). Unlike the other subspecies of X. ulysses, the morphology of the 

right raspula basal to its process in X. ulysses clinias is not suggestive of the structures 

present in X. pubescens and X. gideon that form the cup-like structure [12] in those species. 

Horn size is strongly dimorphic and the allometry is strongly sigmoidal in all the 

populations in which adequate sample sizes were available. The allometric shape of 

specimens from Wau Valley, Papua New Guinea, and Vanuatu is distinctly more sigmoidal 

than in X. ulysses australicus and X. ulysses telemachos and lies to the left of X. ulysses 

ulysses (Figs 48, 49). 

Distribution 

Sulawesi, Moluccas, Papua New Guinea, Solomon Islands, Vanuatu.


Figs 15–18. Raspulae, left lateral view, Xylotrupes pubescens. 15, X. pubescens pubescens from 

Mindanao Island, Philippines; 16, X. pubescens pauliani; 17, X. pubescens zideki; 18, X. pubescens 

baumeisteri. Scale bar = 3 mm. 

Type data 

Xylotrupes clinias: ‘Süd Celebes’, 1 male syntype, examined. X. trasybulus: Key Island, 

male lectotype, 4 male paralectotypes, 4 female paralectotypes (ZMHB), examined; X. 

baumeisteri var. nicias: Sulawesi, male type (ZMHB), examined; X. asperulus: Vanuatu, 3 

male syntypes, 2 female syntypes, examined (ZMHG); X. gideon szekessyi: Bougainville, 

male holotype, 2 male paratypes (HNHM), examined. According to Schaufuss (1885) some 

of the syntypes of X. clinias and X. baumeisteri var. nicias were deposited in the collections 

of Ludwig Salvator and Johann Baumeister. Both of these collections are now reportedly in 

the National Museum in Prague (J. Frisch, J. Zidek, personal communications), but they 

were unavailable for this study. 

X. macleayi: I have treated populations from the Papua New Guinea mainland and Milne 

and Trobriand Islands as X. ulysses clinias (Schaufuss 1885). However, Montrouzier (1855) 

described X. macleayi from Woodlark Island, Papua New Guinea, which is only about 200 

km from the latter islands. Thus, it is quite possible that X. macleayi Montrouzier, 1855 is 

the senior subjective synonym of X. ulysses clinias. Endrödi (1976) reported that the type 

specimen of X. macleayi is in the MNHN in Paris; however, it is in the Institut royal des 

Sciences naturelles, Brussels (D. Drugmand), but is presently unavailable for examination. 

Other specimens examined 

Indonesia: Palu, Sulawesi, 1 male (JMR); Ambon and Buru Islands, 22 males (ZMHB); 

Ceram, 1 male (JMR); Key Island, 1 male (ZMHB); Misool Island, 3 males (ZMHB). Papua


New Guinea: Morobe Province, Wau Valley, 160 males, 4 females (JMR); Milne Islands 

Province, Misima Island, 5 males (JMR) and Tobriand Islands, 22 males (JMR); 

Bougainville Island, 13 males (JMR, HNHM, ZMHB). Vanuatu: Espirito Santo Island, 53 

males and 38 females (JMR); Efate Island, 48 males (JMR). 

Xylotrupes ulysses australicus Thomson, comb. nov. 

(Figs 8, 43, 49; Table 4) 

Xylotrupes australicus Thomson 1859: 18; Schaufuss 1885: 192. 

X. gideon australicus: Endrödi 1951: 246; 1976: 231; 1987: 624. 

Diagnosis 

Males of this taxon are distinguished from the males of X. ulysses ulysses by the more 

hemispherical left raspular base in the latter, from X. ulysses telemachos by the larger right 

and left raspulae, from X. ulysses clinias by the longer right raspular process, respectively, 

in X. ulysses australicus. The right raspular process in X. ulysses australicus is much shorter 

than in X. ulysses falcatus. The allometric shape of the horn length in X. ulysses australicus 

is subtly dimorphic and the allometry is weakly sigmoidal compared with that of X. ulysses 

ulysses and X. ulysses clinias (Fig. 49). 

Distribution 

Northern and eastern Australia, including the islands of the Torres Straits. 

Type data 

‘Nouv.-Hollande’. Types are purportedly in the R. Oberthur Collections (MNHN) (Arrow 

1910), not examined. The type was unavailable for examination; however, its description is 

consistent with the present material, and Australia is well collected and only one taxon has 

been reported (Carne 1957). 


Australia: Queensland: Bundaberg, 426 males, 66 females (JMR) (NMMNH); Mackay, 24 

males, 14 females (JMR) (NMMNH); Heathlands, 3 males (CSIRO); Warraber Island, 

Torres Straits, 6 males (CSIRO). Northern Territory: Darwin, 9 males, 2 females (MNT) 

(PIF). 

Remarks 

This taxon has long been treated as a subspecies of X. gideon by Endrödi (1951, 1976, 

1985). The raspular morphology, however, indicates that this taxon clearly belongs to 

X. ulysses. 

Xylotrupes ulysses telemachos, subsp. nov. 

(Figs 10, 34, 40, 43, 48, 52; Table 4) 

Holotype 

Male. Length from anterior of clypeus to posterior of abdomen 35.5 mm; length from 

posterior margin of pronotum to anterior end of pronotal horn 9.6 mm; pronotal width


Figs 19–24. Raspulae, left lateral view, Xylotrupes mniszechi. X. mniszechi mniszechi: 19, Mussoorie, 

Uttar Pradesh, India; 20, Bushuk, Sikkim. X. mniszechi tonkinensis: 21, Chiang Mai, Thailand; 22, Pac 

Ban, Vietnam; 23, Hainan Island, China; 24, Lanshu Island, Taiwan. Scale bar = 3 mm. 

15.9 mm. Collected at lights in primary forest, elevation 600 m, at Mt Talagaranu, 15 km 

SE of Baru, Halmahera Island, Indonesia, 22–31 January 1996, by Viktor Siniaev and E. 

Tarasov. Deposited in the Museum für Naturkunde der Humboldt Universität, Berlin 

(ZMHB). 

Paratypes 

Seventy-seven males and 28 females collected with the holotype, deposited at ZMHB, QM, 

CSIRO, AMNH, CAS, NHM, JMR, UNSM, USNM.


Diagnosis 

The male is distinguished from males of the other subspecies by its smaller right and left 

raspulae (Fig. 10) and by the restricted upper limits of absolute horn and body size (Figs 48, 

52). In the sample of 78 males, the maximum total length was 42 mm and maximum pronotal 

width was 12 mm. The comparative measures in samples of 426 males of X. ulysses 

australicus from Bundaberg, QLD, Australia, and 35 males of X. ulysses ulysses from 

Namatanai, New Ireland Province, Papua New Guinea, were, respectively, 57 mm, 22 mm, 

81 mm and 24 mm. Horn size is not dimorphic and the allometry is not sigmoidal (Fig. 48). 

Description 

The morphology of the raspulae is shown in Fig. 10, and horn allometry in Fig. 48. 

Measurements (in millimetres) of the holotype and range and mean of 77 male paratypes 

are as follows: abdominal width 21.0 (15.6–21.2, 19.2); elytral length 24.6 (19.0–25.2, 

22.4); pronotal width 15.9 (11.9–16.3, 14.6); pronotum + horn length 9.6 (6.4–12.1, 9.1); 

pronotal length 9.0 (6.3–10.3, 8.5); cephalic horn length 6.5 (3.8–7.9, 5.6). 

Distribution 

Known only from the type locality. One of the collectors (V. Siniaev) indicated that the 

populations of nearby Bacan Island are also very small, and may be referable to this taxon. 

Remarks 

The very small size and size range of the specimens in the type series might suggest that it 

represents a biased sample containing only the very smallest males of a typical, dimorphic 

population. However, when asked this specific question, one of the collectors of this sample 

(V. Siniaev) reported that the specimens were collected at lights, that all specimens 

encountered were collected, that only one or two specimens were separated from the 

original sample, and that these were similar in size to the others. Other factors suggest that 

the size parameters are not an artefact of collecting: these beetles were quite common at the 

type locality, thus it is extremely unlikely that if large or major males were expressed in this 

population, at least a few would not be present in such a large sample; the females in the 

type series, which are not subject to dimorphism, are also uniformly very small; both the 

body size and horn size parameter in this taxon are similar to those of the minor morph of 

other taxa, which, in addition to the previously stated factors, suggests that only the minor 

male morph is expressed in X. ulysses telemachos. 

Etymology 

Telemachos is the son of Ulysses. 

Xylotrupes ulysses falcatus Minck, comb. nov. 

(Fig. 9) 

Xylotrupes falcatus Minck 1920: 220. 

X. gideon lorquini: Endrödi 1951: 244; 1976: 227; 1985: 624. 

Diagnosis 

Males of this taxon are distinguishable from the males of the other taxa of X. ulysses by the 

strongly reflected base of the right raspula and the elongate right raspular process (Fig. 9).


Although only three males are known, one of these has a very long pronotal horn, thus the 

population is probably strongly dimorphic in horn length. 

Distribution 

Known only from Sangi Island, Maluku Province, Indonesia. 

Type data 

‘Sangier’, lectotype male, 2 paralectotype males, 1 paralectotype female (ZMBH), present 

designations. 

Remarks 

Minck (1920) attempted to distinguish this taxon by a combination of characters that are 

unsuitable for this purpose. Endrödi (1951) synonymised this taxon using similarly 

unsuitable characters. The morphology of the raspular complex shows clearly that it is a 

distinct taxon within X. ulysses. 

Xylotrupes pubescens Waterhouse 

(Figs 1, 2, 15–18, 41, 43, 46, 47; Tables 2, 3) 

Xylotrupes pubescens Waterhouse 1841: 539; Thomson 1859: 17, 18; Schaufuss 1885: 191. 

X. baumeisteri Schaufuss 1885: 193. NEW SYNONYMY 

X. gideon pubescens: Endrödi 1951: 245; 1976: 229; 1985: 623. 

X. gideon baumeisteri: Endrödi 1951: 250; 1976: 230; 1985: 624 

X. gideon philippensis Endrödi 1957: 65; 1976: 230; 1985: 624. NOMEN DUBIUM 

X. pauliani Silvestre 1997: 130. NEW SYNONYMY 

Diagnosis 

X. pubescens has a moderately curved right raspular spine [9]; a right raspular cup [12] that 

opens outward rather than downward as in X. mniszechi and X. gideon; and a left raspula 

discretely intermediate in size compared with X. mniszechi and X. gideon (Figs 15–18). The 

small size of the left raspula compared with those of X. ulysses and X. mniszechi and the 

shape of the right raspular spine are considered autapomorphic. The cephalic horn does not 

have a dorsal tooth. The populations of X. pubescens of north Sumatra, south Sumatra, 

Sulawesi and the Philippines are distinctly allopatric, display differences in raspular 

morphology (Figs 15–18) and significant differences in horn allometry (Fig. 47). These and 

other morphological features support recognition of four subspecies. Horn size is strongly 

dimorphic and the allometry is strongly sigmoidal in X. pubescens zideki (Figs 46, 47). 

Sufficient samples of the other subspecies were not available for adequate characterisation 

of their allometric parameters. 

Type data 

See X. pubescens pubescens. 

Synapomorphs 

Xylotrupes pubescens is the sister taxon to the clade of X. mniszechi and X. gideon and 

shares with them the following apomorphs: the left raspula is closed behind [7] (Figs 7–30), 

and is hemispherical in its longitudinal plane [8]; the right raspula has a well developed


Figs 25–30. Raspulae, left lateral view, Xylotrupes gideon. 25, west Java; 26, Gunung Dempo, Sumatra; 

27, Cameron Highlands, west Malaysia; 28, Singapore; 29, Mt Kinabalu, Saba, east Malaysia (Borneo); 

30, Dammar Island, Indonesia. Scale bar = 3 mm. 

cup-like structure below the basal process [12] (Figs 15–18); and the paraproct possesses 

articulation surfaces for the lobes [19]. 

Distribution 

Philippines, southern Sulawesi and Sumatra. 

Xylotrupes pubescens pubescens Waterhouse, stat. nov. 

(Figs 15, 41, 47) 

Xylotrupes pubescens Waterhouse 1841: 539; Thomson 1859: 17, 18; Schaufuss 1885: 191. 

X. gideon pubescens: Endrödi 1951: 245; 1976: 229; 1985: 623. 

X. gideon philippensis Endrödi 1957: 65; 1976: 230; 1985: 624. NOMEN DUBIUM 

Diagnosis 

Compared with the other subspecies, the males of X. pubescens pubescens are 

distinguished by the larger right raspular base (Fig. 15), the presence in some populations


of a hirsute vestiture and dense, strong punctation of the pronotum and elytra. Insufficient 

samples were available for description of horn allometry in this taxon; however, the 

pronotal horn in major males is much shorter compared with that in X. pubescens zideki 

(Fig. 47). 

Distribution 

Philippine Islands. 

Type data 

Philippines. The type is purportedly in NHM (Endrödi 1976), not examined. The identity 

of the type is not in question because the original description contains the following 

unmistakable character that is unique to this taxon: ‘… supra et infra pilis decumbentibus 

vestitut, …’ 


Philippines: Mindanao Island, 3 males, 6 females; Luzon Island, 3 males (AMNH). 

Remarks 

The first male specimens of Xylotrupes described from the Philippines possessed a unique 

vestiture of long hairs on the pronotum and elytra and were given the name X. pubescens 

by Waterhouse (1841). Subsequently, Endrödi (1957) reported that some male Xylotrupes 

in the Philippines are not hirsute, and that hirsute and non-hirsute specimens occur together 

in the same, but unnamed, localities. Endrödi followed a perplexing logic in this paper and 

created the new name X. gideon philippensis for the non-hirsute males and designated the 

hirsute specimens as an aberrant form of X. gideon (‘ab. pubescens’). Little is presently 

known concerning the geographic patterns of male hirsuteness in Philippine Xylotrupes that 

might suggest the phylogenetic significance of this trait. However, I have examined hirsute 

specimens from Mindanao Island and non-hirsute specimens from Luzon Island and found 

no consistent difference in raspular morphology between these populations. Therefore, I 

have reinstated the name X. pubescens for the presently known Philippine populations of 

Xylotrupes, and treat Endrödi’s name, X. gideon philippensis, as a nomen dubium. 

Xylotrupes pubescens zideki, subsp. nov. 

(Figs 1, 2, 17, 46, 47; Table 3) 

Holotype 

Male. Length from anterior of clypeus to posterior of abdomen 40.4 mm; pronotal width 

17.7 mm; length from posterior margin of pronotum to anterior end of pronotal horn 37.4 

mm. Collected at Gunung Dempo, Bengkulu Province, Sumatra, in February 1999. 

Deposited in the Museum für Naturkunde der Humboldt Universität, Berlin (ZMHB). 

Paratypes 

Forty-eight males collected with the holotype, deposited at ZMHB, QM, CSIRO, AMNH, 

CAS, NHM, JMR, UNSM, USNM.


Figs 31–36. Parameres, left lateral view. 31, Trypoxylus dichotomus; 32, Xylotrupes florensis; 33, X. 

meridionalis from Kerala, India; 34, X. ulysses telemachos; 35, X. ulysses clinias from Sulawesi; 36, X. 

gideon from west Java. Scale bar = 6 mm. 

Diagnosis 

The right raspular base of X. pubescens zideki is smaller than that of X. pubescens 

pubescens, but larger than that of X. pubescens baumeisteri (Figs 15–18); it lacks the 

hirsute vestiture and strong punctation of the male’s pronotum and elytra of X. pubescens 

pubescens. Compared with X. pubescens pauliani, it has a longer right raspular process, a 

larger left raspula, lacks the strong pronotal punctation and has much longer relative 

pronotal horn length. Horn size is strongly dimorphic and the allometry is strongly 

sigmoidal, which is located to the left of any other strongly dimorphic species of Xylotrupes 

(Figs 45–51). 

Description 

The morphology of the raspulae is shown in Fig. 17, and horn allometry in Figs 46, 47. 

Measurements (in millimetres) of the holotype and range and mean of 48 male paratypes 

are as follows: abdominal width 23.6 (17.8–24.5, 21.2); elytral length 28.2 (20.9–28.7, 

25.0); pronotal width 17.7 (13.2–18.7, 16.0); pronotum + horn length 37.4 (11.8–38.7, 

24.7); pronotal length 14.7 (8.6–15.4, 12.2); cephalic horn length 20.4 (5.5–22.6, 14.4). 

Distribution 

Known only from the type locality.


Figs 37–42. Paraprocts. 37, Trypoxylus dichotomus; 38, Xylotrupes florensis; 39, X. meridionalis from 

Kerala; 40, X. ulysses telemachos; 41, X. pubescens pubescens; 42, X. gideon from Gunung Dempo, 

Sumatra. Scale bar = 3 mm. 

Remarks 

X. pubescens zideki occurs sympatrically with, but is reproductively isolated from, 

X. gideon. The character displacement in body size relative to horn length between these 

two species on Mt Dempo is unique within the Dynastini and is discussed in detail below. 

Etymology 

This taxon is named for my friend, and multi-talented scientist, Dr Jiri Zidek of Prague.


Xylotrupes pubescens baumeisteri Schaufuss, stat.nov. 

(Figs 18, 47) 

Xylotrupes baumeisteri Schaufuss 1885: 192. 

X. gideon baumeisteri: Endrödi 1951: 245; 1976: 230; 1985: 624. 

Diagnosis 

Compared with the other subspecies of X. pubescens, the males of X. pubescens 

baumeisteri are distinguished by the much smaller right raspular base (Fig. 18). Insufficient 

samples were available for description of horn allometry in this taxon; however, the 

pronotal horn in relation to body size in the two male syntypes, both minor males, is similar 

to that of X. pubescens pubescens and X. pubescens pauliani, but much shorter than that of 

X. pubescens zideki (Fig. 47). 

Distribution 

Known only from the type series. 

Type data 

Sulawesi (‘Süd Celebes’), one male syntype; Makassar, 1 male syntype; ‘S. Celebes’, 2 

female syntypes (ZMHB), examined. According to Schaufuss (1885), some of the syntypes 

of X. baumeisteri were in the collections of Ludwig Salvator and Johann Baumeister. Both 

of these collections are reportedly now in the National Museum, Prague (J. Zidek, J. Frisch, 

personal communications), but were unavailable for this study. 

Remarks 

Examination of the raspulae of the two syntypes of X. baumeisteri (ZMHB) shows clearly 

that they belong to X. pubescens (Figs 15–18), as here defined. However, Schaufuss (1885) 

described a variety of X. baumeisteri, also from Sulawesi that he named ‘var. nicias’. 

Examination of that specimen reveals that it is identifiable with X. ulysses clinias, above. 

It is important to note that both X. pubescens baumeisteri and X. ulysses clinias occur in 

south Sulawesi and that further collections in that region may yield evidence concerning 

sympatry and possible character displacement. 

Xylotrupes pubescens pauliani Silvestre, stat. nov. 

Xylotrupes pauliani Silvestre 1997: 130. 

(Figs 16, 47) 

Diagnosis 

Males are distinguished from the other subspecies in having dense and strong lateral 

pronotal punctation; the length of the right raspular base is shorter than in X. pubescens 

pubescens, longer than in X. pubescens baumeisteri and similar to that of X. pubescens 

zideki, but the left raspula is smaller than in X. pubescens zideki; allometric shape is 

unknown.


Type data 

Male holotype (MNHN), Medan, Doloc Baros, Sumatra, examined; 55 male and 8 female 

paratypes (MNHN) from northern Sumatra, and east and west Malaysia were designated by 

Silvestre (1997), but none of these were examined by me to confirm identity with the 

holotype. 

Remarks 

The holotype, upon which the present taxonomic placement is based, is from Medan, 

northern Sumatra; however, Silvestre (1997) also designated paratypes from west Malaysia 

and Borneo. He distinguished this taxon principally by the combination of its small size, 

strong and dense punctation of the pronotum, lack of a cephalic horn tooth, form of the 

parameres and ocular canthus – some characters of which I have found to be of questionable 

value. Moreover, I was able to examine only the holotype of X. pauliani, thus the identity 

of the paratypes, especially those from west Malaysia and Borneo, remains of interest. 

Xylotrupes mniszechi Thomson 

(Figs 19–24, 43, 51; Table 2) 

Xylotrupes mniszechii Thomson 1859: 18; Minck 1920: 218. 

?X. socrates Schaufuss 1863: 60. 

X. tonkinensis Minck 1920: 217. 

X. siamensis Minck 1920: 217 (syn. Endrödi 1951: 244). 

X. gideon mniszechi: Endrödi 1951: 245; 1985: 623. 

X. gideon tonkinensis: Endrödi 1951: 245; 1976: 229; 1985: 623. 

?X. gideon kaszabi Endrödi 1951: 245; 1976: 230; 1985: 624. 

X. gideon socrates: Endrödi 1951: 245. 

Diagnosis 

X. mniszechi is characterised by a strongly angled right raspular spine [9], but which is not 

as strongly angled as in X. gideon; and a moderately large right raspular bulb [10], but 

which is not as long as in X. gideon (Figs 19–24). Horn size in X. mniszechi tonkinensis 

from Chiang Mai is strongly dimorphic and the allometry is strongly sigmoidal, but the 

horns of X. mniszechi mniszechi from Sikkim are very small and non-dimorphic. 

Expression of a cephalic horn tooth is variable within and among populations. 

Type data 

See X. mniszechi mniszechi. 

Synapomorphs 

X. mniszechi and X. gideon exclusively share the following apomorphs: some males of X. 

mniszechi and most males of X. gideon express a cephalic horn tooth [2] (Fig. 1); the angle 

of the right raspular spine is more acute than in other taxa [9] (Figs 19–30); they possess a 

well developed bulb-like enlargement at the angle of the right raspular spine [10]; and the 

basal raspular piece is long [13]. 

Distribution 

Himalaya region, south-east Asia, China, and Lanshu Island, Taiwan.


Remarks 

The populations of the Himalaya region differ in raspular morphology and horn allometry 

from the populations of south-east Asia and China, which is the basis for recognition of two 

subspecies. 

Xylotrupes mniszechi mniszechi Thomson, stat. nov. 

(Figs 20, 51) 

Xylotrupes mniszechii Thomson 1859: 18; Minck, 1920: 218. 

?X. socrates Schaufuss 1863: 60. 

X. gideon mniszechi: Endrödi 1951: 245; 1976: 229; 1985: 623. 

Diagnosis 

Compared with X. mniszechi tonkinensis, the males of this taxon are distinguished by a 

smaller right raspula and less strongly angled right raspular spine (Figs 19–24). None of the 

males express a cephalic horn tooth. A large sample from Sikkim has smaller pronotal and 

cephalic horns and horn size ranges than any other population of Xylotrupes (Figs 45–51). 

Distribution 

Himalaya region. 

Type data 

Xylotrupes mniszechi: Simla, Himachal Pradesh, India. Types are reportedly in the R. 

Oberthur Collections (MNHN) (Arrow 1910; Endrödi 1976) but were unavailable for study. 

It was assumed in this study that specimens from Mussoorie, about 100 km SE of the type 

locality, which are consistent with the original and subsequent descriptions of the types 

(Minck 1920; Endrödi 1951, 1976, 1985), adequately represent the types. No evidence 

suggests that any other taxon occurs with 1000 km of this region. 


India: Mussoorie, Uttar Pradesh, 3 males, 1 female (AMNH); Bushuk, Sikkim, 82 males, 

51 females (JMR). Two male syntypes of X. socrates Schaufuss 1863 (ZMHB) from Nepal 

were examined but these specimens lack genitalia, thus their identification with this taxon 

is conjectural. 

Xylotrupes mniszechi tonkinensis Minck, stat. nov. 

(Figs 21–24, 51) 

Xylotrupes tonkinensis Minck 1920: 217. 

X. siamensis Minck 1920: 217 (syn. Endrödi 1951: 244). 

X. gideon tonkinensis: Endrödi 1951: 245; 1976: 229; 1985: 623. 

?X. gideon kaszabi Endrödi 1951: 245; 1985: 624. 

Diagnosis 

See X. mniszechi mniszechi above for raspular morphology. A large sample of X. mniszechi 

tonkinensis from Chiang Mai is strongly dimorphic and the allometry is strongly sigmoidal.


Expression of a cephalic horn tooth is variable both within and among populations of X. 

mniszechi tonkinensis and is not correlated with body or horn size. 

Distribution 

South-east Asia and China. 

Type data 

X. tonkinensis: Laos, male lectotype, 9 male paralectotypes (ZMHB), examined. X. 

siamensis: Thailand, male lectotype, Siam and 1 male paralectotype (ZMHB), present 

designation. 


X. gideon kaszabi: Ning Po, China, male ‘monotype’ (HNHM), examined. Thailand: 

Chiang Mai, 94 males (JMR); Chiang Dao, 40 males (JMR); Kho Chang Island, 21 males 

(JMR). Taiwan: Lanshu Island, 1 male, 1 female (JMR). China: Hainan Island, 1 male 

(JMR). Vietnam: 7 males (ROM). India: Assam, 6 males, 3 females (JMR). 

Remarks 

The type of X. gideon kaszabi is the only known specimen from the region of Ning Po, 

China; thus, I examined the internal sac only sufficiently to identify it as belonging to X. 

mniszechi, and did not fully dissect it in order to carefully compare the raspular morphology 

with other populations of this subspecies; thus its identification as X. mniszechi tonkinensis 

is tentative. 

Xylotrupes gideon (Linnaeus) 

(Figs 1, 2, 25–30, 36, 42–46; Tables 2, 3) 

Scarabaeus gideon Linnaeus 1767: 541. 

S. oromedon Drury 1770: 81. (syn. Thomson 1859: 17). 

S. phorbanta Olivier 1789: 17 (syn. Arrow 1910: 262). 

Geotrupes dentatus Weber 1801: 35 (syn. Endrödi 1985: 623). 

S. scorticum Voets 1806: 32 (syn. Endrödi, 1976: 226). 

S. simson Voets 1806: 25 (syn. Endrödi 1976: 226). 

S. nimrod Voets 1806: 25 (syn. Thomson 1859: 17). 

S. furciger Voets 1806: 70 (syn. Thomson 1859: 17). 

S. alcibiades Dejean 1833: 167 (syn. Thomson 1859: 17). 

Xylotrupes beckeri Schaufuss 1885: 17; Silvestre 1997: 127. 

X. beckeri var. metzneri Schaufuss 1887: 123 (syn. Silvestre 1997: 127). 

X. inarmatus Sternberg 1906: 172 (syn. Endrödi 1951: 244). 

X. gideon gideon: Minck 1920: 218; Endrödi 1951: 251; 1976: 230; 1985: 623. 

X. sumatrensis Minck 1920: 218. 

X. borneensis Minck 1920: 218. 

X. bourgini Paulian 1945: 196 (syn. Endrödi 1976: 226). 

X. gideon beckeri: Endrödi 1951: 244; 1985: 624. 

X. gideon sumatrensis: Endrödi 1951: 251; 1976: 227; 1985: 624; Silvestre 1997: 124. 

X. gideon borneensis: Endrödi 1951: 250; 1976: 226; 1985: 624; Silvestre 1997: 125. 

Diagnosis 

Raspular autapomorphs (Figs 27–30) include a very strongly angled right raspula [9]; a 

very large right raspular bulb [10]; a very long right raspular process originating on the


mesal aspect of the raspula and upon which the left raspula is articulated distally; the 

downward reflection of the left raspular cup [12]; the very small size of the left raspula; and 

the median lobe of the aedeagus has a lyriform distal invagination. This taxon is also 

characterised by the possession of a cephalic horn tooth in almost all males [2] and the 

convoluted distal shape of the left paraproct plate. Horn size in populations of Java, Sumatra 

and northern west Malaysia is strongly dimorphic and the allometry is strongly sigmoidal. 

Two males from Borneo, however, have a much smaller horn size relative to body size than 

in the former populations (Fig. 45) and only minor males are known from the Lesser Sunda 

Islands. 

Distribution 

West Malaysia; Borneo; Indonesian archipelago from Sumatra and Java, east through the 

Lesser Sunda Islands at least to Dammar Island. 

Type data 

X. gideon: The earliest species-group name applicable to Xylotrupes is Scarabaeus gideon 

Linnaeus, 1767. However, there is presently little useful evidence concerning the 

geographic origin of the specimen(s) upon which Linnaeus based that name. The single 

specimen in the Linnaeus collection at the Linnaean Society, which he probably had before 

him when he described X. gideon, does not have collecting data, and now the head is 

missing. Fortunately, however, Linnaeus noted that his type possessed a cephalic horn tooth 

(‘… capitis (cornu) recurvato supra unidentato’), which suggests that this specimen will 

prove to be consistent either with X. gideon or with X. mniszechi, as here defined. The only 

related facts are that Linnaeus (1767) indicated for X. gideon, ‘Habitat in Indiis’, but later, 

in his copy of Systema Naturae, he interlined ‘Indiis’ and pencilled in ‘Africa’ (M. Fitton, 

personal communication), but which is clearly an incorrect locality. However, the 

geographic origin of X. gideon eventually became generally referred to as Java in the 

scientific literature (e.g. Guérin-Méneville 1830). On the basis of tradition and convenience 

and because no reasonable evidence contradicts it, it is assumed in this study that the 

Linnaeus type is identifiable with the typical populations that I have studied from west Java. 

X. beckeri: Singapore, male lectotype, male syntype (ZMBH), examined. X. beckeri var. 

metzneri: Malacca, male lectotype (ZMBH), examined. X. sumatrensis: Sumatra, male 

lectotype (ZMBH), not examined. X. borneensis: Borneo, male lectotype (ZMBH), not 

examined. 


Indonesia: Gunung Dempo, Bengkulu Province, Sumatra, 92 males (JMR); Burung, Riau 

Province, 6 males (JMR); Lampung Province, Sumatra, 178 males (JMR); west Java, 146 

males (JMR); Bali Island, 1 male (JMR); Sawu Island, 2 males (JMR); Flores Island, 5 

males, 14 females (JMR); Timor Island, 7 males (JMR, ZMHB); Dammar Island, 2 males 

(ZMHB). West Malaysia: Cameron Highlands, west Malaysia, 12 male (ZMHB, JMR); Mt. 

Kinabalu, Borneo, 2 males (USNM). 

Subspecies 

I have not yet been able to examine sufficient material of this widespread species to support 

a comprehensive subspecific classification. However, Endrödi (1951, 1976, 1985) 

recognised four taxa that are certainly referable to X. gideon as defined herein. He treated 

the populations of Java as X. gideon gideon, of Sumatra as X. gideon sumatrensis, of Borneo


as X. gideon borneensis, and of west Malaysia as X. gideon beckeri. Examination and 

comparisons of hundreds of specimens from south Sumatra and west Java, however, 

suggests that it is unlikely that these populations should constitute different taxa but that 

both should constitute X. gideon gideon. 

Males from Mt Kinabalu, Borneo, have a much shorter pronotal horn than those from 

south Sumatra and west Java. Males from the Cameron Highlands, west Malaysia, have a 

longer basal raspular piece than in the other populations; they also have a somewhat shorter 

and wider pronotal horn than do those of south Sumatra and west Java. 

Schaufuss (1863) described X. beckeri on the basis of specimens from Singapore. 

Subsequently, Endrödi (1951, 1976, 1985) referred to all the populations of west Malaysia 

as X. gideon beckeri. Silvestre (1997) designated a lectotype and provided a redescription 

of X. beckeri and reasserted its species rank. Unfortunately, in preparation of the aedeagus, 

the internal sac was discarded and the raspular anatomy of this specimen is now lost. Thus, 

the designation by Silvestre of a lectotype and the concomitant destruction of the internal 

sac of this specimen prevents me from making a certain identification of this specimen and 

the name based upon it. The median lobe of the aedeagus of the lectotype possesses a 

lyriform distal invagination, which suggests that it is probably consistent with X. gideon as 

herein defined; however, it lacks a distinct cephalic horn tooth. A specimen from Singapore 

(ZMBH) probably represents the same taxon as the type of X. beckeri, which, by raspular 

and parameral morphology, clearly belongs to X. gideon (Fig. 28) and, consistent with the 

lectotype of X. beckeri, does not express a cephalic horn tooth. Moreover, these two 

specimens from Singapore, the type of X. beckeri metzneri from ‘Malacca’, west Malaysia, 

and six males from Burung, Riauw Province, Sumatra, approximately 100 km from 

Singapore, probably represent a distinct, short-horned population of X. gideon. This 

population lacks, or only weakly expresses, a cephalic horn tooth; and thus far appears to 

occur in the lowland areas of southern west Malaysia, Singapore and adjacent lowlands of 

Sumatra and very likely might be recognised as X. gideon beckeri, if the above difficulties 

created with the lectotype can be overcome. 

Silvestre (1997) also described X. beckeri wiltrudae from Borneo. As with the lectotype 

of X. beckeri, the internal sac was discarded during preparation of the genitalia of the 

holotype of X. beckeri wiltrudae and I am presently unable to make certain assignment of 

this taxon. The latter specimen has a cephalic horn tooth, the median lobe of the aedeagus 

possesses a lyriform distal invagination, and thus is probably identifiable with X. gideon. 

Remarks 

X. gideon was obtained for this study from two Indonesian islands, Flores and Timor, from 

which only X. florensis had previously been reported. The collections of X. gideon and X. 

florensis on Flores Island were obtained in the same habitats, about 45 km east of Labuan 

Bajo, which is evidence of reproductive isolation between X. gideon and X. florensis. 

Phylogenetic analysis 

Although the relationships are not well understood among the genera of the Dynastini, of 

which Xylotrupes is a member, it became apparent through examination of representatives 

of all of these genera that Trypoxylus (frequently Allomyrina) dichotomus is the sister group 

of Xylotrupes. Specimens of T. dichotomus, Xyloscaptes davidis, Allomyrina pfeifferi, 

Megasoma actaeon, M. thersites, Dynastes granti, Golofa pelagon, Augosoma centaurus, 

Eupatorus gracilicornus, Chalcosoma caucasus and Cyphonistes vallatus were used for 

outgroup comparisons.


The rationale for assigning polarities is discussed explicitly for each character. 

Assignment of primitive or derived character states for relative lengths of the cephalic and 

pronotal horns in major males [1], presence of a cephalic horn tooth [2] and bifurcation of 

the apex of the mandible [3] are qualified relative to the other taxa within the Dynastini, 

inasmuch as these characters appear to have been subject to multiple reversals within the 

Dynastini and the Dynastinae. Synapomorphs and autapomorphs are described for the 

relevant taxa in the systematics section. Explanation is provided for decisions concerning 

reversals and convergences, and the consequences of alternative interpretations. 

PAUP version 4.1 (Swofford 1998) was used to determine the phylogenetic relationships 

of the taxa. The number of steps, the consistency index and the retention index are reported 

for the most likely phylogenetic scheme. 

Characters 

Pronotal and cephalic horns [1] (Fig. 1) 

The species of Xylotrupes share with Trypoxylus, Megasoma and Cyphonistes bifurcate 

pronotal and cephalic horns in the males. Xylotrupes, however, is the only one of these taxa 

in which the pronotal horn is longer than the cephalic horn in major males, which is thus 

considered the derived state. Within the context of all the dynastine genera, however, this 

condition in Xylotrupes may represent a reversal inasmuch as the major males of Dynastes, 

Augosoma and Golofa possess long pronotal horns. 

Cephalic horn tooth [2] (Fig. 1) 

A cephalic horn tooth is expressed in some or all species of Xylotrupes, Megasoma, 

Dynastes, Augosoma and Chalcosoma, but not in Trypoxylus. Therefore, the expression of 

a cephalic horn tooth is considered derived; however, this state may represent a reversal 

relative to other dynastines. 

The cephalic horn tooth in X. mniszechi and X. gideon is located mid-dorsally and is 

blade-shaped in major males. A small local protuberance that has been referred to by the 

same name is present distally on the cephalic horn of X. meridionalis, just at the base of the 

apical tines and is bluntly conical in shape. Since the anatomical location and the 

architecture of the latter structures in these species are distinct, these were coded as 

convergent derived states. 

Mandible [3] 

Among the Dynastini, the apex of the mandible bears a single tooth or has two teeth. In 

Trypoxylus dichotomus, most species of Megasoma and X. florensis, the apex of the 

mandible has a single tooth. The other species of Xylotrupes have two apical teeth. Thus, 

relative to Trypoxylus, the presence of two apical mandibular teeth is a derived state in 

Xylotrupes. Since two mandibular teeth are present in Augosoma, Dynastes, Golofa and 

some species of Megasoma, the same state in Xylotrupes may represent a reversal to the 

primitive state within the context of the Dynastini. 

Raspular complex [4, 5, 6] (Figs 3–30) 

The raspulae of the internal sac of the aedeagus in most genera of the Dynastini consist 

of a chagrine of minute spines or hairs and is considered the primitive condition. In 

T. dichotomus and Xylotrupes, however, the raspular complex is composed of two or three 

large, sclerotised structures herein termed the right raspula, the left raspula and the basal


raspular piece. In T. dichotomus, the left raspula is a single large spine [4] with a more or 

less conical base. In Xylotrupes, except X. florensis, the left raspula is a single large spine, 

as in T. dichotomus, with a base that is triangular or oval in lateral aspect. Possession of a 

single large left raspular spine in T. dichotomus and Xylotrupes is thus considered derived 

relative to the chagrine of minute spines in other dynastines. 

The form of the right raspula [5] in T. dichotomus is elongate, elevated and strongly 

sclerotised and composed of a compound series of strong spines and is considered a derived 

state relative to the chagrines of minute spines present in most of the Dynastini. The form 

of the right raspula in Xylotrupes is also elongate, elevated and strongly sclerotised but is 

composed as a single large spine. 

All the taxa of Xylotrupes, except X. florensis, possess an additional element proximal 

to the right and left raspulae which is herein called the basal raspular piece [6]. Absence or 

indistinct development of this structure in T. dichotomus, as in all the other Dynastini, is 

considered primitive. Its presence in Xylotrupes is derived and its greater length in 

X. mniszechi and X. gideon is considered a further derivative state [13]. 

In X. florensis, the raspular complex is represented by a single, relatively small spine on 

the right side. The presence of large and strongly sclerotised raspular elements in 

T. dichotomus and all the other taxa within Xylotrupes suggests that the right and the left 

raspulae have become much reduced or secondarily lost, respectively, in X. florensis. The 

left raspula [4] in X. florensis is absent and is treated as a reversal to the primitive state. 

Since a distinctly sclerotised basal raspular piece is not present in T. dichotomus or 

X. florensis, it cannot presently be inferred whether the absence of the basal raspular piece 

in X. florensis is the ancestral condition, or a reversal to it. 

Left raspula [7, 8] (Figs 3, 5–30) 

In T. dichotomus, X. meridionalis and X. ulysses, the form of the left raspular base [7] is 

essentially triangular in lateral aspect and broad and open at the proximal end, which is 

considered primitive. In X. pubescens, X. mniszechi and X. gideon, the left raspular base is 

more ovoid in lateral aspect, narrower proximally and is closed in by a strong margin, which 

is derived. The distinct difference in shapes of the left raspular base between the former set 

of taxa and X. pubescens and X. mniszechi is related to an apparent partial encapsulation of 

a duct that leads into the internal sac and opens at the base of the left raspular spine in 

X. pubescens. However, due to extreme reduction in size of the left raspular base in 

X. gideon, the homologies with respect to X. pubescens and X. mniszechi are obscure. 

The shape of the left raspular base in its longitudinal plane [8] is distinctly flat in 

X. meridionalis and X. ulysses, but hemispherical in X. pubescens, X. mniszechi and 

X. gideon. The polarity of this character was determined partly on developmental grounds, 

inasmuch as the hemispherical shape appears to be accomplished by a convolution of the 

distal margin of the base and formation of the sclerotised foramen that partly encompasses 

the above duct. This structure is especially evident in X. pubescens and X. mniszechi, but is 

not suggested in T. dichotomus, X. florensis, X. meridionalis and X. ulysses. 

Right raspula [9, 10, 11, 12] (Figs 3–30) 

The shape of the right raspula [9] is more or less uniformly curved through its length in 

T. dichotomus, X. florensis, X. meridionalis, X. ulysses and X. pubescens, but in 

X. mniszechi and X. gideon it is more strongly angled in the area of a bulb-like enlargement 

[10]. The strong angle of the right raspula and the presence of a bulb-like enlargement of 

the spine are considered derived because neither are suggested in T. dichotomus.


Composition of the right raspula [11] in T. dichotomus is constituted by a series of about 

30 spines, each about 0.7 mm long, and a large number of minute spines. These appear to 

be homologous to, and developed from, the chagrine of minute spines that constitute the 

raspulae in other dynastines. In Xylotrupes, however, the right raspula is constituted by a 

single strong spine, about 3–5 mm long, that has apparently formed from the fusion of 

several smaller spines. Constitution of the right raspula [11] as a series of smaller spines 

with a chagrine of minute spines is considered primitive. The right raspula constituted as a 

single large spine is considered derived. 

The right raspula in Xylotrupes, except X. florensis, possesses an anteriorly projecting 

process of variable development. It is generally located closer to the base of the raspula in 

X. ulysses and more distally in X. pubescens, X. mniszechi and X. gideon and is associated 

with articulation of the base of the left raspula. This process in X. gideon is large and long, 

and bears articulation of the small left raspula. A long, forward-projecting process also 

occurs in X. meridionalis, but this structure originates on the lateral surface rather than the 

mesal surface and does not serve as an articulation point for the left raspula, and thus is 

considered a convergent derived state. In X. pubescens, X. mniszechi and X. gideon, the 

form of the base of the right raspula [12], below the process for articulation of the left 

raspula, is developed as an open cup-like invagination defined by development of a lateral 

wall that extends down from the articular process. This configuration is not developed in 

T. dichotomus, X. florensis, X. meridionalis and X. ulysses, and is considered derived in the 

former taxa. In some populations of X. ulysses, the basal process is very small and located 

close to the proximal end (Figs 11–14), but in other populations the basal process is larger 

and located more distally (Figs 7–10). The architecture of the raspula below this process in 

the latter populations is similar to and may be homologous with those features that form the 

cup-like structure in X. pubescens, X. mniszechi and X. gideon. This alternate interpretation 

and its effects on the phylogenetic scheme is illustrated in Fig. 43. See further discussions 

under X. ulysses, below. 

Length of basal raspular piece [13] 

Among the Dynastini, a basal raspular piece [6] is suggested in T. dichotomus only by a 

basal area of indurated or slightly sclerotised tissue proximal to the left and right raspulae 

and is well developed only in Xylotrupes. This structure, however, varies in length among 

the taxa. It is relatively short in X. meridionalis and X. ulysses and relatively long in 

X. gideon and some populations of X. mniszechi. In certain populations of X. gideon the 

basal piece is very long. The homology of the basal raspular piece in Xylotrupes to the 

indurated tissue in T. dichotomus is tentatively inferred, thus the assignment of polarity to 

the relative size of the basal raspular piece is made partly on developmental grounds that 

the lesser length is ancestral and that greater length is derived. 

Parameres [14] (Figs 31–36) 

In all genera of Dynastini, other than Xylotrupes, the blades of the male’s parameres 

extend in virtually the same plane as the lateral walls, forming the orifice of the parameres. 

However, in all Xylotrupes except X. florensis, the blades angle strongly upward, which is 

considered a derived state. 

Paraproct [15, 16, 17, 18, 19] (Figs 37–42) 

The paraproct plates in Dynastes, Megasoma, T. dichotomus and X. florensis are 

relatively symmetrical [15], rounded apically [16], and the midline of the lobes and the


Fig. 43. Phylogenetic trees. Alternative trees for possible relationships among Trypoxylus dichotomus 

and the species of Xylotrupes. The minimal length topology represents the strict consensus tree 

discovered by the exhaustive search algorithm of PAUP 4.1 using 19 characters. The trees have a 

consistency index of 0.91, a retention index of 0.94 and a length of 21 steps. The tree to the right is the 

alternate branching sequence indicating possible paraphyly in X. ulysses depending upon alternate 

interpretation of homologies in the structures of the right raspula [12]. X. ulysses A = X. ulysses clinias; 

X. ulysses B = X. ulysses ulysses, X. ulysses australicus, X. ulysses falcatus and X. ulysses telemachos. 

The characters are explained in the text and Table 1. HTU = hypothetical taxonomic unit. C = 

convergence; R = reversal. 

midline of the paraproct plates are located close to the same parasaggital planes [17], which 

represent the ancestral states of these characters. The paraproct plates in X. meridionalis are 

symmetrical but are strongly acuminate distally, which is the derived state, and the lobes are 

located distinctly more lateral to the paraproct, which is the derived state. In X. ulysses, 

X. pubescens, X. mniszechi and X. gideon, the paraproct plates are distinctly asymmetric, 

acuminate, and the lobes are located lateral to the paraproct, which are all considered 

derived conditions. 

All the taxa with asymmetric paraproct plates possess a horizontal blade on the mesal 

surface of the right side that inserts into a corresponding invagination on the mesal surface 

of the left side [18], which is considered derived. 

In X. pubescens, X. mniszechi and X. gideon the distolateral margins of the paraproct 

possess a well defined planar surface for articulation of the lobes [19]. This articular 

surface is not present in Dynastes, Megasoma, T. dichotomus, X. florensis, X. meridionalis 

or X. ulysses. Presence of this articular surface on the paraproct is thus considered derived.


Table 1. Characters and character polarities used in the phylogenetic analysis 

The character polarities were determined for the hypothetical ancestral taxon, Trypoxylus dichtomus and 

the species of Xylotrupes according to rationale explained in the text. Ancestral states are coded as 0, 

derived states as 1. The complete data matrix is presented in Table 2 

Horns 

01. Relative length of cephalic and pronotal horns in major males: 0, cephalic horn longer than 

pronotal horn; 1, pronotal horn longer than cephalic horn. 

02. Cephalic horn tooth: 0, absent; 1, present. 

Mandible 

03. Apex of mandible: 0, one tooth; 1, two teeth. 

Raspulae 

04. Left raspular spine: 0, absent; 1, present. 

05. Right raspular form: 0, not elongated or heavily sclerotised; 1, elongate and heavily sclerotised. 

06. Basal raspular piece: 0, absent; 1, present. 

07. Left raspula base: 0, open behind; 1, closed behind. 

08. Shape of the left raspular base in longitudinal plane: 0, flat; 1, hemispherical. 

09. Shape of right raspular spine: 0, uniformly curved; 1, strongly angled. 

10. Bulb of right raspula: 0, absent or indistinct; 1, well developed. 

11. Composition of right raspula: 0, a series of separate small spines; 1, a single large spine. 

12. Cup-like structure at base of right raspula: 0, absent or indistinct; 1, well developed. 

13. Basal raspular piece: 0, absent or short; 1, long. 

Parameres 

14. Orientation of paramere blades: 0, same plane as orifice; 1, angled toward orifice. 

Paraprocts 

15. Paraproct plates: 0, symmetrical; 1, asymmetrical. 

16. Paraproct shape: 0, apically rounded; 1, apically acuminated. 

17. Position of paraproct lobes: 0, midline similar to paraproct plates; 1, midline lateral to paraproct 

plates. 

18. Mesal surfaces of paraproct plates: 0, not interdigitating; 1, interdigitating. 

19. Distal planar surface on paraproct for articular of lobes: 0, absent; 1, present. 

Table 2. Data matrix for phylogenetic analysis of the species of Xylotrupes 

Ancestral states were determined by explicit rationale presented in the character analyses and presented 

in Table 1 

Taxon Character 

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 

Ancestor 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 

T. dichotomus 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 

X. florensis 1 0 0 0 1 0 0 0 0 0 1 0 0 0 0 0 0 0 0 

X. meridionalis 1 1 1 1 1 1 0 0 0 0 1 0 0 1 0 1 1 0 0 

X. ulysses 1 0 1 1 1 1 1 1 0 0 1 1 0 1 1 1 1 1 1 

X. pubescens 1 0 1 1 1 1 1 1 0 0 1 1 0 1 1 1 1 1 1 

X. mniszechi 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 

X. gideon 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 

Results 

The trees in Fig. 43 illustrate two possible phylogenetic relationships of species within 

Xylotrupes discovered by the exhaustive search in PAUP 4.1 using 19 characters. These 

solutions have a consistency index of 0.91, a retention index of 0.94 and lengths of 21 steps. 

Alternative interpretations of homology and character coding are discussed below relative 

to their effects on the trees. A summary of the characters and their polarities is given in 

Tables 1 and 2.


The phylogenetic analysis indicates that only two apomorphs distinguish Xylotrupes 

from other dynastine genera, but the combination of other characters support the 

assumption that this genus is monophyletic. Only two apomorphs also distinguish 

X. meridionalis from the taxon constituted by X. ulysses, X. pubescens, X. mniszechi and 

X. gideon; thus the latter branching event might be viewed with less certainty than are the 

other three bifurcations in the primary tree, which are each characterised by at least four 

synapomorphic steps (Fig. 43). 

As further explained in the descriptions of the characters and the taxa, the cephalic horn 

bears a dorsal tooth [2] in X. gideon and some populations of X. mniszechi. The latter 

structure is questionably homologous to a structure found in X. meridionalis that is given 

the same name by various authors (Minck 1920; Endrödi 1951, 1976, 1985). The analysis 

treats the latter as a convergence; however, its treatment as a synapomorph requires only 

one extra step. Similarly, absence of the basal raspular piece [6] is coded as an apomorph 

for HTU 11 (Fig. 43); however, the general reduction or loss of other raspular elements 

suggests that absence of the basal raspular piece in X. florensis may be a reversal and a 

synapomorph in the remainder of the species of Xylotrupes, which requires only one 

additional step. The long right raspular processes in X. gideon and X. meridionalis, as 

previously described, are treated as convergent autapomorphs, inasmuch as treatment as 

synapomorphs requires two extra steps and three reversals. 

The alternate branching sequence for a portion of the phylogenetic tree is shown to the 

right in Fig. 46 and reflects the possible paraphyly in X. ulysses based upon alternate 

interpretation of the homologies of the structures of the right raspulae [12] in X. ulysses and 

HTU 10. These are discussed in detail in the descriptions of the characters and taxa. 

Horn dimorphism 

While dimorphism is an obvious feature of horn-size frequency distributions in Xylotrupes 

(e.g. Fig. 44) and other horned beetles, it has proven difficult to apply quantitative methods 

that identify and statistically differentiate variations on the bimodality (Eberhardt and 

Gutierrez 1991). However, the allometric function (e.g. Fig. 45) that produces the 

dimorphism can readily serve to measure differences in horn expression because it can be 

quantified and statistically analysed by regression techniques. Eberhard (1987), Eberhard 

and Gutierrez (1991) and Emlen (1996) have developed regression models that 

discriminate variations in several allometric parameters. 

The principal parameters of interest in this study are allometric position and allometric 

shape. Allometric position is the location of the bivariate distribution relative to the 

horn-length axis and to the body-size axis, which can be measured in two dimensions. 

Allometric shape is the form of the plot of the bivariates. In taxa with monomorphic horns 

the shape of the bivariate distribution is simple and often more or less linear. In taxa with 

dimorphic horns, there is a switch or inflection point in the allometry. Dimorphism can be 

produced by a difference in slope on either side of the switch point, or by a vertical 

discontinuity at the switch point. It is the latter discontinuity that produces the sigmoidal 

allometry. 

Eberhard and Gutierrez (1991) developed a piece-wise linear regression model that 

is used herein to detect bimodality as a discontinuity in the allometric function. Emlen 

(1996) introduced a non-linear regression methodology to differentiate subtle effects on 

allometric position induced by directional artificial selection. The latter model was 

converted herein to a more standardised logistic function that scales broadly to horn 

length and is used to measure variations in allometric shape and position.


Figs 44, 45. 44, Bimodal frequency distribution of horn length, Xylotrupes gideon, Lampung Province, 

Sumatra, Indonesia. 45, Allometric relationships of horn length and body size, Xylotrupes gideon. Crosses: 

Lampung Province, Sumatra; open circles: Gunung Dempo, Bengkulu Province, Sumatra; closed triangles: 

Mt Kinabalu, Borneo. 

Figs 46, 47. Allometric relationships of horn length and body size. 46, Sympatric populations of 

Xylotrupes gideon and X. pubescens zideki from Gunung Dempo, Sumatra, which illustrates character 

displacement between these species. Open circles: X. gideon; closed circles: X. pubescens zideki. 47, 

Xylotrupes pubescens. Closed circles: X. pubescens zideki; open circles, open triangles: X. pubescens 

pubescens from Luzon Island, and Mindanao Island Philippines; closed square: X. pubescens pauliani; 

cross: X. pubescens baumeisteri.


Figs 48, 49. Allometric relationships of horn length and body size, Xylotrupes ulysses. 48, Closed 

circles: X. ulysses telemachos; open circles: X. ulysses clinias from Wau Valley, Papua New Guinea; closed 

triangles: X. ulysses ulysses. 49, Dots: X. ulysses australicus from Bundaberg, Queensland; open triangles: 

X. ulysses clinias from Vanuatu. 

Figs 50, 51. Allometric relationships of horn length and body size. 50, Sympatric populations of 

Xylotrupes florensis and X. gideon from Tado lands, Flores Island, Indonesia. Closed circles: X. florensis; 

open squares: X. gideon. 51, Xylotrupes mniszechi. Closed circles: X. mniszechi mniszechi from Sikkim. 

X. mniszechi tonkinensis: open circles: Chiang Mai, Thailand; closed squares: Kho Chang Island, 

Thailand; crosses: Vietnam; closed triangles: Assam, India; large closed circle: Lanshu Island, Taiwan.


Model forms: 

Y = β 0 + β 1 X + β 2 (X – c)D + β 3 D 

where Y = horn length; X = body size; D = 0 if X < c, otherwise D = 1; and the parameters 

are β 0 = Y at X = 0; β 1 = slope of minor male distribution; β 1 + β 2 = slope of major male 

distribution; c = body size at the discontinuity; and β 3 = size of the discontinuity at X = c. 

Y = e + 2/(d – e) [(X/c) b / (1 + (X/c) b ) – 0.5] 

where the parameters are c = lateral position (body size at centre of the modelled bivariate 

distribution); e = vertical position (horn size at centre of the modelled bivariate distribution, 

at X = c); b = slope; and d = horn length at modelled asymptote. 

The horn-length and body-size variates are caliper measurements in increments of 0.1 

mm from the midline of the posterior margin of the pronotum to the apical end of the 

longest tine of the pronotal horn, herein termed ‘pronotum + horn length’ (pronotal 

extension length in Cook 1987) and greatest width of the pronotum, a conventional estimate 

for body size (Eberhard and Gutierrez 1991; Emlen 1996; Moczek and Emlen 1999). 

Representation of horn length as ‘pronotum + horn length’ is a practical necessity because 

there is no other distinct pronotal landmark besides its posterior margin that can serve as a 

consistent point from which to measure. This step, however, adds a relatively large element 

in these measures that presumably covaries with body size. This added component of body 

size, however, did not interfere with discrimination of minor and major morphs in this 

study, or in Ageopsis nigricollis (Eberhard 1987). 

Allometric shape and position – ancestral and derived states 

Horn allometry is distinctly sigmoidal in many of the Dynastini including Trypoxylus 

dichotomus, the sister taxon of Xylotrupes. In at least some populations of X. florensis, X. 

ulysses, X. pubescens, X. mniszechi and X. gideon the allometry is strongly sigmoidal and 

the position of inflection of the sigmoid occurs near 20–25 mm of pronotum + horn length 

and 17–19 mm of pronotal width (Figs 44–51). It is thus inferred that a significant vertical 

discontinuity in the allometry is the ancestral state for Xylotrupes and the state from which 

other allometric shapes and positions in Xylotrupes were derived. The allometries of several 

other populations, however, are distinctly different from the former populations in shape 

and/or position. The present quantitative analysis measures differences in allometric 

position between sympatric populations of X. gideon and X. pubescens zideki on Gunung 

Dempo, Sumatra and differences in allometric shape and position among widespread 

populations of X. ulysses. 

The evolutionary changes manifested in the latter taxa are associated with distinctly 

different selective environments: one in which character displacement occurs between 

sympatric, but reproductively isolated taxa, and another in which the changes in allometry 

are explained by geographic variation among allopatric taxa. 

Allometry and secondary sexual character displacement in Xylotrupes 

It was discerned in this study that X. gideon and X. pubescens zideki are sympatric on Mt 

Dempo, Sumatra. These populations have similar allometric shapes, but distinctly different 

lateral allometric positions (Fig. 46). It is hypothesised that this difference in relative horn 

size is a result of character displacement as an adaptation to interspecific


Table 3. Variations in parameters of horn allometry in sympatric and allopatric populations 

of Xylotrupes 

The non-linear regression model (see text) produced parameter estimates for the sympatric 

populations of X. gideon and X. pubescens zideki at Gunung Dempo, Bengkulu Province, Sumatra, 

and X. gideon from Lampung Province, Sumatra. Significant differences were identified by 

pair-wise t-tests between X. gideon from Gunung Dempo and the other populations 

Parameter X. gideon X. pubescens zideki X. gideon 

Gunung Dempo Gunung Dempo Lampung Province 

n = 93 n = 49 n = 178 

Lateral position (‘c’) 185.5 ± 3.9 159.1 ± 1.60 190.0 ± 10.90 

P < 0.0000 n.s. 

Vertical position (‘e’) 256.2 ± 19.2 241.4 ± 9.30 283.3 ± 52.90 

n.s. n.s. 

Slope (‘b’) 012.6 ± 3.4 021.9 ± 5.70 009.3 ± 3.500 

n.s. n.s. 

Asymptote (‘d’) 432.3 ± 50.1 366.3 ± 20.1 495.6 ± 129.1 

n.s. n.s. 

competition between closely related, sympatric species competing for similar resources 

(Grant 1972). Model confirms that the allometric shape, horn-length asymptote and 

vertical position of the distributions are quite similar in the two species, but that there is a 

highly significant, 2–3-mm symmetrical displacement in body size per given horn length. 

Parameter estimates and pair-wise comparisons are reported in Table 3. 

Allometric parameters of X. gideon at Gunung Dempo are statistically indistinguishable 

from those of populations of X. gideon from the lowlands of Lampung Province (Table 3, 

Fig. 45), and in west Java, where X. pubescens zideki is absent. This strongly suggests that 

the character displacement evident at Gunung Dempo has occurred principally at the 

expense of the latter species. This is supported by the observation that X. pubescens zideki 

is shifted far and significantly (Wilcoxon, P < 0.004) to the left in lateral position relative 

to the other populations of X. pubescens (Fig. 47). 

Geographic variations of allometry in Xylotrupes 

Greater diversity in the parameters of horn allometry occurs among the populations of 

X. ulysses than in the other species (Figs 48–54). Allometric shape is strongly sigmoidal in 

X. ulysses clinias and X. ulysses ulysses, but the lateral allometric positions are different. 

Allometric shape is weakly sigmoidal in X. ulysses australicus and non-sigmoidal in X. 

ulysses telemachos (Figs 48, 49). X. ulysses ulysses and X. ulysses telemachos represent the 

extremes in Xylotrupes of absolute body and horn sizes, body and horn size ranges, and 

lateral and vertical allometric positions (Figs 48, 49). In order to quantify and statistically 

analyse these variations, pairwise comparisons of the allometric parameters were made 

between a sample of X. ulysses clinias from Wau Valley, Papua New Guinea, to each of the 

other taxa using the non-linear regression model . This model shows that there exist 

large and highly significant differences in both allometric shape and position among 

various populations of X. ulysses. Parameter estimates and pair-wise comparisons are 

reported in Table 4. 

The statistical comparisons of X. ulysses ulysses were impeded by its small sample size. 

Thus, while the means for horn length asymptote, vertical and lateral position are all 

considerably greater than in X. ulysses clinias, only the latter parameter was statistically 

significant. X. ulysses australicus had a significantly lower vertical position and a reduced


Table 4. Variations in parameters of horn allometry in allopatric populations of Xylotrupes ulysses 

The non-linear regression model (see text) produced parameter estimates for select subspecies of X. 

ulysses. Significant differences were identified by pair-wise t-tests between X. ulysses clinias from Wau 

Valley, Papua New Guinea, and the other populations 

Parameter X. ulysses clinias X. ulysses clinias X. ulysses ulysses X. ulysses australicus 

Wau Valley, PNG Vanuatu New Ireland, PNG Queensland 

n = 160 n = 53 n = 36 n = 426 

Lateral position (‘c’) 172.7 ± 1.60 181.1 ± 1.30 223.3 ± 24.10 175.5 ± 1.4 

P < 0.0001 P < 0.05 n.s. 

Vertical position (‘e’) 207.3 ± 6.20 243.0 ± 6.50 364.5 ± 151.7 163.4 ± 3.1 

P < 0.0001 n.s. P < 0.0001 

Slope (‘b’) 017.0 ± 3.00 025.9 ± 5.00 013.1 ± 9.600 009.9 ± 1.0 

n.s. P < 0.05 P < 0.05 

Asymptote (‘d’) 319.6 ± 10.6 347.7 ± 11.8 588.3 ± 337.0 256.4 ± 8.6 

n.s. n.s. P < 0.0001 

slope compared with X. ulysses clinias. Model did not converge in the case of 

X. ulysses telemachos because the bivariate distribution for this taxon is non-sigmoidal. 

Lack of convergence in this model is strongly indicative of a fundamentally different 

allometric shape in X. ulysses telemachos compared with the ancestral state. Samples of 

X. ulysses clinias from Wau Valley, Papua New Guinea, and from Vanuatu were found to 

have small but statistically significant differences in both lateral and vertical allometric 

positions. 

Allsopp (1991) showed that horn length distribution in a small sample of X. ulysses 

australicus from Queensland did not differ significantly from normality and unimodality. 

However, the present, much larger sample indicates that a subtle bimodal distribution is 

present in this population. This is detected as a significant vertical discontinuity in the 

allometric function Model (P < 0.001) and is visible as a slight sigmoid in the bivariate 

distribution (Fig. 49). The horn size distribution is much less clearly bimodal in X. ulysses 

australicus relative to other taxa because the vertical discontinuity in the allometric 

distribution is smaller, effecting more proximal locations of the major and minor horn 

length modes and an obscure intermode. 

Horn allometry in a large sample of X. mniszechi tonkinensis from Chiang Mai, 

Thailand, is strongly sigmoidal. However, populations of X. mniszechi mniszechi from 

Sikkim have extremely small horns, horn size range and a non-dimorphic horn size 

distribution (Fig. 51). Variations between these taxa parallel those between the strongly 

dimorphic X. ulysses clinias and the non-dimorphic X. ulysses telemachos. 

The horn allometry in large samples of X. gideon from various localities in southern 

Sumatra and west Java are indistinguishable. On the other hand, two males of this species 

from Borneo show a clearly reduced overall allometric slope compared with those of 

southern Sumatra (Fig. 45). Similar findings were made relative to X. pubescens, wherein 

the Sumatran X. pubescens zideki occupies a lateral position distinctly to the left of the 

Philippine X. pubescens pubescens. 

Samples of Xylotrupes from the western lowlands of Flores Island, Indonesia, produced 

males and females of both X. florensis and X. gideon. Four of the five males of X. gideon 

are smaller in body and horn size compared with X. florensis and may indicate that 

character displacement occurs between these species on Flores Island (Fig. 50).


Discussion 

Evolution of horn dimorphism in Xylotrupes 

The patterns of horn allometry (Figs 44–51) relative to the phylogenetic analysis (Fig. 43) 

indicate that a strongly sigmoidal allometry is the ancestral state in Xylotrupes. While the 

ancestral state is expressed in at least some populations of five of its species, several of 

these species also have subordinate lineages that diverge markedly from the ancestral 

condition, which indicates a ready capacity in Xylotrupes for evolutionary modifications in 

horn dimorphism. One species, in particular, X. ulysses, in which it was possible to study 

rich and diverse collections, demonstrates the propensity for presumably rapid evolutionary 

modifications in both allometric position and allometric shape parameters among its 

lineages. 

Evolutionary lability of the allometric parameters in Xylotrupes differ qualitatively 

compared with those reported by Emlen (1996) in the scarabaeine dung beetle genus 

Onthophagus. A principal finding in the latter study was that the metric relationship of horn 

size to body size responded strongly to artificial selection with lateral changes in allometric 

position but not in allometric shape. In addition to the experimental results, Emlen (1996) 

reported that significant variation exists in horn and body size ranges and allometric 

position among the five American species of Onthophagus studied, but that, consistent with 

the experimental studies, allometric shape is uniformly sigmoidal among those species. The 

question was thus posed whether, in general, allometric shape might be less subject to 

evolutionary change than is allometric position in horned beetles and other groups of 

organisms with similar non-linear allometries. The present findings, however, indicate that 

allometric position is much less variable among the taxa of Xylotrupes than among the taxa 

of Onthophagus, and that allometric shape is more variable. 

Allometric position and character displacement 

Symmetric variation of allometric position in Xylotrupes, i.e. a relatively uniform shift of 

the entire horn size distribution relative to body size is clearly evident among allopatric 

populations of X. ulysses (Figs 48, 49; Table 4) and between the sympatric populations of 

X. pubescens zideki and X. gideon (Figs 2, 46; Table 3). However, these variations are small 

compared with those reported among the species of Onthophagus. For example, where they 

are sympatric in Sumatra, pronotal width in X. pubescens zideki is about 85% that of X. 

gideon in the region of inflection of the sigmoid (Fig. 46), whereas pronotal width of the 

smallest of five American species of Onthophagus is only 40% of that in the largest species 

(Emlen 1996). 

The similar allometric shapes, but distinctly different allometric positions, in X. gideon 

and X. pubescens zideki (Fig. 46) are evidence of a classic character displacement (Grant 

1972) as an adaptation to interspecific competition between closely related, sympatric 

species. The discovery of sympatric species of Xylotrupes in which character displacement 

has occurred involving the developmental system producing male horn dimorphisms 

provides an important example of its macroevolutionary behaviour. Two observations 

suggest that body size has evolved downward in X. pubescens zideki in order to 

accommodate sympatry with X. gideon. The allometric positions of the other populations 

of X. pubescens are located considerably to the right of those from Gunung Dempo (Fig. 

46), whereas the allometric position of X. gideon at Gunung Dempo is indistinguishable 

from populations of X. gideon in the regions of Sumatra and west Java where X. pubescens 

zideki is absent (Fig. 45; Table 3). While the coexistence of X. gideon and X. pubescens


zideki on Gunung Dempo, Sumatra, is thus evidently predicated upon a smaller body size 

in the latter, none of this reduction in body size has come at significant expense to horn size. 

It is therefore apparent that the selective advantage of large horn size and horn size range 

in X. pubescens zideki compensates the cost of significantly greater proportional 

developmental investment in these sexual ornaments. Such is not the case in the only other 

relevant example of character displacement in horned beetles. Where sympatric, both body 

size and horn size are approximately equally displaced in Chalcosoma caucasus and C. 

atlas compared with allopatric populations (Kawano 1995a, 2002) 

Collections from the following regions of known or possible sympatry among the 

species of Xylotrupes could yield rich additional evidence concerning the evolutionary 

behaviour of secondary sexual character displacement: X. florensis and X. gideon in the 

Lesser Sunda Islands; X. ulysses and X. pubescens in Sulawesi; X. mniszechi and X. gideon 

in the south-western coastal provinces of Thailand; X. ulysses and X. gideon in Sulawesi and 

eastern Borneo; and X. mniszechi and X. meridionalis in central India. 

In contrast to the symmetric variations in allometric position among the above taxa of 

Xylotrupes, the positional modifications in X. ulysses telemachos and X. ulysses australicus 

are asymmetric and engage qualitatively different adaptive mechanisms involving 

allometric shape. 

Allometric shape 

The ancestral state of allometric shape in Xylotrupes is a well defined sigmoid with at least 

a 3-mm vertical discontinuity, which is present in X. florensis, X. pubescens zideki, 

X. mniszechi tonkinensis, X. gideon, X. ulysses ulysses and X. ulysses clinias (Figs 45–51). 

Allometric shape, however, is markedly at variance with the ancestral state in X. ulysses 

australicus, X. ulysses telemachos and X. mniszechi mniszechi. 

In X. ulysses australicus, the overall slope of the bivariate distribution and the vertical 

discontinuity of the sigmoid are greatly reduced compared with the ancestral state (Fig. 49). 

The latter factors, combined with a smaller maximum horn size, effect a reduction in the 

morphological distance between major and minor horn length modes, thereby obscuring the 

intermode and apparent differentiation of the two morphologies. Comparison of the 

behavioural and ecological traits of the Australian population to the strongly dimorphic 

taxa of X. ulysses may thus identify disruptive selective forces that favour maintenance of 

alternate male morphologies. 

Horn expression in X. ulysses telemachos and X. mniszechi mniszechi is qualitatively 

different from that in the other taxa of Xylotrupes inasmuch as these taxa show no evidence 

of bimodality or sigmoidality in horn size. The horn sizes and horn size ranges are so 

constrained that allometric shape in these taxa might have arisen not through reduction in 

bimodality and sigmoidal shape, as in X. ulysses australicus, but through a qualitatively 

different mechanism. Moreover, it is possible that the condition-dependent ontogenetic 

switch that produces major and minor morphologies is inoperative in X. ulysses telemachos 

and X. mniszechi mniszechi, and that only the minor morph is expressed (see taxonomic 

section). 

Modelling allometric shape 

The developmental mechanism that produces horn dimorphism often manifests a vertical 

discontinuity at the inflection point of the bivariate distribution, which thus produces 

bimodality through a rapid increase in horn length over a relatively narrow range of body 

sizes (Eberhard 1987; Eberhard and Gutierrez 1991; Emlen 1996). For some such species,


the relationship of horn size to body size has been described as rigid, with no small major 

males and no large minor males (Eberhard 1982). However, the latter description, while 

fitting the general algorithm for the average relationship of horn size to body size in many 

dimorphic beetles, does not accurately characterise the actual distributions in other species. 

In the large dynastine Chalcosoma caucasus horn length is distinctly bimodal (Kawano 

1995a, 1995b, 2002), while the range of body sizes over which the transition of minor to 

major male horn sizes occurs is not narrow but extremely wide. In a sample of 206 males 

the range in horn length in minor and major males is 3–30 mm and 28–49 mm, respectively, 

whereas the range of body lengths in minor males is 45–79 mm and that of major males is 

57–82 mm. Relatively high variation of body sizes, especially in the region of the inflection 

of the sigmoid, is observed not only in the two species of Chalcosoma but, to some extent, 

also in Dynastes (Kawano 1995a, 1995b), Augosoma (Bowden 1959), Xylotrupes and 

perhaps in species of other genera, e.g. Onthophagus incensus (Eberhardt and 

Gutierrez 1991). 

Moreover, the developmental program that produces major or minor male morphologies 

might cause horn length to increase rapidly over a narrow range of body sizes only if this 

developmental system also imposes constraints on maximum body size in minor males and 

minimum body size in major males. A rigid and narrow association of horn size to body 

size may characterise those taxa in which the developmental switch is operative only at the 

end of the larval development. However, if the switch can occur early in the larval 

development, then the distribution of minor and major male morphs might occur over a 

much broader range of body sizes, as in Chalcosoma. 

Behavioural correlates of horn dimorphisms 

In the scarabaeine dung beetle genus Onthophagus, the behavioural correlates of dimorphic 

horn expression are known in detail. Major males defend reproductive access to selected 

females, whereas minor males employ sneaking tactics to intercept females and avoid 

combat with other males (Emlen 1996, 1997). Major males also cooperate with females in 

brood provisioning, while minor males do not (Cook 1988, 1990). These behaviours are 

surmised to contribute to the disruptive selective environment that favors horn 

dimorphisms in Onthophagus (Emlen 1996). It is not presently known what discrete 

behavioural traits accompany the alternate male morphologies in dimorphic populations of 

Xylotrupes. However, that such correlated behavioural traits are manifested in Xylotrupes 

is strongly suggested by the observation that in the closely related taxon Trypoxylus 

dichotomus minor males fly earlier in the evening to potential mating sites than do major 

males and avoid combat with major males (Siva-Jothy 1987). In another dynastine, 

Podischnus agenor, minor males also appear earlier in the annual breeding cycle and 

disperse more widely than major males (Eberhard 1982). 

It has been reported for Javan populations of X. gideon (Bateson and Brindley 1892) that 

captive major males, when presented with the opportunity, seized females transversely 

between their horns and carried them about, and that minor males made ineffectual efforts 

to do so. The latter behaviour might demonstrate a function for the horns in honest signaling 

of male competitive ability, and thus provide a model in which to further test the hypothesis 

that condition-dependent male ornaments may improve both male intrasexual competitive 

ability and male attractiveness to females (Kodric-Brown and Brown 1984; Hunt and 

Simmons 1997).


Fig. 52. Largest and smallest males of Xylotrupes ulysses ulysses (above) and X. ulysses telemachos 

(below) from unbiased samples; n = 35 and n = 76, respectively. Scale = life size. 

Behavioural traits and indirect genetic effects on horn morphology 

Beetles of the family Scarabaeidae, especially in the Dynastinae and the Scarabaeinae, have 

evolved a prodigious variety of horn shapes and sizes that have long provoked questions 

about their function, evolutionary origin and maintenance (Darwin 1871). However, it is not 

until recently that the genetic basis of these structures has begun to be explored (Emlen 1996; 

Moczek and Emlen 1999). Considering the great diversity in horn morphology among these 

beetles, it was thus a seemingly remarkable finding in the latter studies that male horn length 

has little or no heritable variation in either of two investigated species of Onthophagus. 

Recent research, however, has identified brooding behaviour in Onthophagus as a potential 

source of indirect genetic contributions to horn morphology (Hunt and Simmons 2000). 

Possible macroevolutionary evidence that such indirect genetic effects might function in this


way on horn morphology is provided in the greater diversity of horn shapes in Onthophagus, 

in which parental care is highly developed, compared with the lesser diversity of horn shapes 

in Xylotrupes and other genera of the Dynastini in which parental care is apparently much 

less developed. Other macroevolutionary evidence, however, offers little support for a broad 

positive relationship between male parental investment in dung beetles (Halffter and 

Matthews 1966; Halffter and Edmonds 1982) and diversification of male horn morphology 

in those taxa. It has even been suggested by Arrow (1951) that male participation in nest 

construction and brood provisioning by tunnelling dung beetles is impeded by the physical 

imposition of large horns, and Moczek and Emlen (2000) report that in Onthophagus taurus 

possession of horns reduces male agility in brood tunnels. Moreover, the importance of 

indirect mechanisms of sexual selection on horn shapes might be revealed in the 

macroevolutionary patterns of behavioural traits associated with them. 

Diversification in Xylotrupes 

This study documented diversification and speciation in Xylotrupes in large part through 

use of primary sexual characters. More significantly, however, these results also illustrate 

that evolutionary modification in male horn allometry is not only an additional principal 

feature of speciation, but also of infraspecific diversification. 

Examination of rich collections of X. ulysses reveals particularly marked variation in 

allometric parameters, especially allometric shape, among its populations (Figs 48, 49, 52; 

Table 4). In X. ulysses ulysses and X. ulysses clinias the major and minor morphs are well 

differentiated by a strongly sigmoidal horn size distribution. In X. ulysses australicus this 

differentiation is statistically demonstrable but subtle and in X. ulysses telemachos only a 

single male phenotype is evident and the allometric shape is essentially linear. Notably, the 

latter taxon and X. ulysses ulysses (Fig. 48) represent the extremes of variation in allometric 

position and shape among the taxa of Xylotrupes. 

Moreover, variation in horn allometry relative to phylogenetic scale indicates that the 

developmental system controlling male horn dimorphism in Xylotrupes has been subject to 

rapid evolutionary modifications. These modifications are principal features of speciation 

and intraspecific diversification in this group. The taxa of Xylotrupes may thus provide new 

perspectives concerning the ecological, social and competitive circumstances that produce 

evolutionary change in male horn dimorphism and are the object of ongoing investigation. 

Acknowledgments 

Johannes Frisch (ZMBH) provided an extraordinary amount of valuable material and other 

assistance to this study, without which, much less progress in the taxonomic revisions 

would have been accomplished. Clifford Qualls (UNM) assisted greatly with the 

quantitative methods. Jiri Zidek (Prague), Johannes Frisch (ZMBH), David Edmonds 

(Marfa, TX) and Brett Ratcliffe (UNLSM) critiqued the manuscript. Norm Platnick 

(AMNH) provided advice concerning the classification. Andy Heckert (NMMNH) ran the 

PAUP program. Specimens and other valued assistance were provided by Greg and Rod 

Llewallen (Combined Scientific Supply, Fort Davis, TX), Peter Allsopp (Bureau of Sugar 

Experiment Stations, Bundaberg, Australia), Thomas Weir (CSIRO), Jeanine Pfeiffer 

(ECO-SEA, Davis, CA), Henderikus Eddy and the Tado community (Flores Island, 

Indonesia), Kazuo Kawano (Kobe University), Mike Fitton and Malcolm Kerley (NHM), 

Lee Herman (AMNH), Chris Darling and Brad Hubley (ROM), Nicole Berti (MNHN), 

Otto Merkl (HNHM), Laurence Ollivier (CIRAD, Montpellier), Scott Fay (Namatanai 

Secondary School, Papua New Guinea), Joachim Adis (Max-Planck-Institut für


Limnologie, Plön), Roberta Brett (CAS), Al Samuelson (Bishop Museum, Honolulu), Beth 

Norden (USNM), Viktor Siniaev (Moscow), Charles Mutti (Evangelical Bible College, 

Mufumbwe, Zambia), Lora Lee Kerr (University of Minnesota, St Paul) and Beverly Pope 

(Florida Department of Agriculture, Gainesville). 

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Manuscript received 8 February 2002; accepted 25 March 2003 

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