Taxonomy and Evolution of Gibbons

Primatology and Anthropology 29Diploid NumberTABLE 1. Main Divisions of Genus Hylobates aOther DivisionGenusof Chromosomes Names Species English-Language NameHylobates 44 lar group H. agilis b Agile gibbonH. klossii Kloss’s gibbonH. lar White-handed gibbonH. moloch Silvery gibbonH. muelleri c Müller’s gibbonH. pileatus Pileated gibbonBunopithecus 38 B. hoolock HoolockNomascus 52 concolor group, N. concolor Western black crested gibboncrested gibbonsN. sp. cf. nasutus Eastern black crested gibbonN. gabriellae Yellow-cheeked crested gibbonN. leucogenys d White-cheeked crested gibbonSymphalangus 50 S. syndactylus Siamanga Raising the four main groups of gibbons to genus rank follows the consensus reached at the workshop “Primate Taxonomy forthe New Millennium” (February 25–29, 2000, Orlando, Florida), to be presented in a future publication, and reference 20.b Including H. agilis albibarbis.c Including H. muelleri abbotti and H. muelleri funereus.d Including N. leucogenys siki.The trees based on vocal characteristics(Fig. 1c) are similar to those ofdata set 2. Bunopithecus hoolock appearsin an unusually basal position inthe tree, however, because of its manyapparently primitive vocal characteristics.Hylobates klossii is identified asthe sister taxon of H. moloch.The various standard measures calculatedin order to assess the “quality”of trees are shown in Table 2 (bootstrapvalues, CI, RI, and RC). Data set1 scores distinctly worse in all variablesthan the other two data sets. Thedifference between data sets 2 and 3 isless distinct in these variables. Nevertheless,data set 3 has higher values inall of these variables (especially inbootstrap values) than set 2, indicatingthat particularly “good” trees aregenerated with vocal data.The mean pairwise distances betweengibbon taxa are shown in Figure2. Fur coloration data are able todifferentiate not only between speciesand genera, but also between subspecies.Both the range and standard deviationof the distances are extremelylarge, however, and show a broadoverlap among different systematiclevels. This means that differences infur coloration provide little informationon the genetic distance betweenany two taxa. Two subspecies may bemore different in fur coloration thanmembers of two different genera.“Noncommunicatory” data, on theother hand, do not differentiate wellbetween subspecies, and the standarddeviations for subspecies and speciesoverlap. These data differentiate betweensome, but not all, species. Thepairwise differences between membersof different genera are distinctlygreater than those between species,and standard deviations for speciesand genera do not overlap.The vocal data produce similar resultsto the “noncommunicatory”data. This data set does not differentiatebetween subspecies at all, butdifferentiates well between speciesand genera. Standard deviations ofsubspecies, species, or genera do notoverlap.The three data sets also differ in thespecies groups they support (Table 2).TABLE 2. Various Parameters of Trees in Figure 1, and Topologies of Gibbon Taxa Supported by These Trees aData Set Set 1 Set 2 Set 3Number of Characters 37 34 34Type of Tree S B S B S BTree length 158 191 73 78 88 90Number of bootstrap values above 50 5 5 10Number of shortest trees 2 117 1Consistency index (CI) 0.49 0.41 0.66 0.62 0.67 0.66Retention index (RI) 0.63 0.47 0.80 0.77 0.81 0.80Rescaled consistency index (RC) 0.31 0.19 0.53 0.47 0.54 0.52Monophyly of agilis and albibarbis Monophyly of concolor group Monophyly of lar group (44-chromosome gibbons)H. hoolock as sister group of lar group H. klossii sister of all other members of largroup a et 1, fur coloration data; Set 2, “noncommunicatory” data; Set 3, vocal data. S, shortest tree; B, Bootstrap 50% majority-ruleconsensus tree; , supported; , not supported.