systematics of snakes of the dipsas oreas complex - BioOne

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76 Bulletin Museum of Comparative Zoology, Vol. 158, No. 3 tice a few other subtle differences between the two (see below). Peters (1960a), although he elucidated the pattern of geographic variation, did not differentiate the population samples as distinct taxonomic entities or associate the name ‘‘Dipsas elegans’’ with one of the population samples. Kofron (1982: 50) further suggested that ‘‘A comprehensive analysis of D. oreas and D. [elegans] may show the two to be subspecifically related, as I can distinguish the specimens . . . only by pattern.’’ Kofron’s (1982: 50) use of the name D. ellipsifera throughout the last paragraph of his text is an apparent lapsus for D. elegans in view of his synonymizing the former name with the latter earlier in the paper (Kofron, 1982: 48). Orcés and Almendáriz (1987) acted on Peters’ observations of geographic variation and examined additional specimens of both Dipsas elegans and D. ellipsifera. Unfortunately, in their reconsideration of the geographic pattern, they again lumped specimens by locality without regard to sex and thus failed to elucidate the correlation between sexual dimorphism in meristic data and geography that had been outlined by Peters (1960a). On the basis of average differences in meristic characters between population samples and little or no overlap in segmental counts between them, Orcés and Almendáriz (1987) maintained D. elegans and D. ellipsifera as distinct taxonomic entities but, following Kofron’s (1982: 50) suggestion, considered them subspecies of D. oreas Cope. Orcés and Almendáriz provided the new combinations Dipsas oreas elegans and Dipsas oreas ellipsifera. The taxonomic justification was based on the broad overlap in ventral and subcaudal counts between nominotypical D. oreas and D. elegans (Orcés and Almendáriz, 1987: 138) and on the similar color patterns of D. elegans and D. ellipsifera. The relationship, if any, of Dipsas elegans and D. ellipsifera to D. oreas warrants renewed scrutiny. Peters (1960a: 30–31) defined species groups on the basis of color pattern characteristics. This was unfortunate because color patterns are highly variable within some species of Dipsas. Nonetheless, Peters’ oreas group included D. elegans, D. ellipsifera, and D. oreas by virtue of having a color pattern in which ‘‘the blotches are wider than the interspaces, with little contrast in color between them (pl. IVa) [and] the centers of the blotches are considerably lightened, which often gives the species an appearance of having paired ellipses on the sides....Theinterspaces are rather heavily streaked and spotted with dark colors’’ (Peters, 1960a: 31). A glance at the photograph that Peters chose to illustrate color patterns characteristic of the oreas group (Peters, 1960a: Plate IVa) shows that even this example does not fit the definition well (e.g., some of the interspaces are wider than the blotches and the the color pattern exhibits great contrast). Examination of only a few specimens will quickly erode confidence in Peters’ definition of the oreas group. In all three species of the oreas group, the width of the blotches (or bands) varies along the length of the body; anteriorly, they are virtually always wider than the interspaces, but posteriorly, they are narrower than the interspaces. Most specimens of all three species have highly contrasting patterns (see later discussion of D. oreas for some exceptions, Cadle and Myers [2003: 21– 25], the photograph of the holotype in Kofron [1982], and later discussion and illustrations herein). The similarity and uniqueness of the color patterns of Dipsas elegans and D. ellipsifera, and their narrowly allopatric distributions (documented herein), suggest a close relationship between the two species. However, the similarity in segmental counts between Dipsas elegans and D. oreas, particularly among females (see Table 1), is of minimal consequence in assessing a possible relationship or conspecificity between them because many species of Dipsas have broadly overlapping scale counts (Cadle and Myers [2003] and subsequent discussions herein of D. gracilis). Thus,
Dipsas oreas Complex in Ecuador and Peru • Cadle 77 there seems to be little to unify D. elegans, D. ellipsifera, and D. oreas as a ‘‘species group,’’ Peters’ (1960a) color pattern characteristic notwithstanding. The color patterns of D. elegans and D. ellipsifera in reality bear little resemblance to that of D. oreas. Moreover, D. andiana, which Peters (1960a, 1965) considered a synonym of D. oreas, seems to be more closely related to D. nicholsi of Panama than to D. oreas (Cadle and Myers, 2003: 32–34). As emphasized by Cadle and Myers (2003), interspecific relationships among species of Dipsas need to be reassessed with a broader, more comprehensive set of characters than currently exists. Thus, the species groups elaborated by Peters (1960a) can be considered categories only of convenience. Nonetheless, as will be shown, all three species of the oreas group are unusual with respect to sexual dimorphism in ventral counts compared with typical colubrid patterns. Dipsas oreas and D. ellipsifera show no sexual dimorphism in ventral counts, whereas D. elegans is highly unusual in that males have higher ventral counts than females. Whether these characteristics are restricted to the oreas group or are more broadly distributed within Dipsas requires study of additional species. A casual survey of data for other species of Dipsas at hand (Table 4 for D. gracilis and several species considered by Cadle and Myers [2003]) suggests that unusual patterns of sexual dimorphism in segmental counts might prevail within this genus. Thus, with respect to Peters’ ‘‘oreas group,’’ I address questions concerning the proper definition and diagnoses of the included species without necessarily implying any phylogenetic unity to the group. Despite their previous confusion in much of the previous literature, careful study shows that Dipsas elegans, D. ellipsifera, and D. oreas can be distinguished from one another by a combination of scutellational, color pattern, and dentition characteristics. For these reasons I resurrect D. elegans and D. ellipsifera from the synonymy of D. oreas, and recognize all three taxa as valid species. I herewith provide differential diagnoses for these species and summarize their systematics, geographical distributions, and natural history. A summary of variation in standard systematic characters for these species (Table 1) will be helpful in following the ensuing diagnoses and descriptions. Dipsas ellipsifera (Boulenger) Figures 2–8 Leptognathus ellipsifera Boulenger, 1898: 117. Lectotype BMNH 1946.1.21.26 (Fig. 2, Table 2) designated herein. Type locality, ‘‘Ibarra’’ [Ecuador]. Werner, 1922: 197. Sibynomorphus ellipsifer: Amaral, ‘‘1929’’b [1930]: 197. Dipsas ellipsifera: Peters, 1960a: 87. Peters, 1965: 3. Peters and Orejas-Miranda, 1970: 86. Dipsas elegans, part: Peters, 1960a: 87, 91–92 (referred specimens from the western slopes of the Andes in Ecuador exclusive of those from the Río Mira drainage, specifically including those from ‘‘Camino a Mindo,’’ ‘‘El Corazón,’’ and ‘‘near Peñaherrera’’). Kofron, 1982: 48. Miyata, 1982: 16. Dipsas oreas ellipsifera: Orcés and Almendáriz, 1987: 138. Pérez-Santos and Moreno, 1991: 156. Notes on the Type Series and Designation of a Lectotype The syntypes of Leptognathus ellipsifera comprise four specimens obtained by W. F. H. Rosenberg and sent to the British Museum of Natural History: BMNH 1946.1.21.26–29 (original numbers 98.4.28.87–90). The original description (Boulenger, 1898) simply noted ‘‘several specimens.’’ Data on the syntypes are presented in Table 2, and the largest male, BMNH 1946.1.21.26 (Fig. 2), is hereby designated the lectotype. The smallest of the paralectotypes, BMNH 1946.1.21.27, was illustrated by Kofron (1982: fig. 1), and the lectotype and female paralectotype (BMNH 1946.1.21.28) are illustrated herein (Figs. 2, 3). A fine artistic rendering of the head and anterior body of the female paralectotype (the largest specimen) was given in the original description (Boulenger, 1898: pl. XII, fig. 2). The lectotype is an adult male in good
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Dipsas oreas Complex in Ecuador and
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