Geissmann, T. 2000: A reassessment of the evolution and adaptive radiation of gibbons. In: The apes: Challenges for the 21st century. Brookfield Zoo, May 10-13, 2000, Chicago Zoological Park, Chicago, p. 37 (Abstract only).

A reassessment of the evolution and adaptive radiation of gibbons

T. Geissmann

Institute of Zoology, Tierärztliche Hochschule Hannover, Bünteweg 17, Hannover D-30559, Germany

Because the fossil history of gibbons is virtually unknown, gibbon evolution can only be reconstructed from a comparative analysis of evolutionarily informative characteristics of modern gibbons and, to some degree, of related primate taxa that can be used as outgroups. Several studies tried to reconstruct gibbon phylogeny using fur coloration, morphological, vocal, or molecular data. Each study produced a different result. As a result, the relationships among the various hylobatids are under debate and even the evolutionary relationships among gibbon genera (Symphalangus, Nomascus, Bunopithecus, and Hylobates) remain unresolved.

For the present study, I collected three different data sets of about equal size in order to assess their relevance for a reconstruction of gibbon phylogeny using cladistic methods. Set one uses characteristics of fur coloration, set two consists primarily of morphological and anatomical data, and set three consists of vocal data. I present a re-evaluation of data sets 1-3, as well as phylogenetic trees resulting from a cladistic analysis of each.

Gibbons appear to have undergone such a radical "rebuilding" since their split from the last common ancestor with the other modern hominoids that it is difficult to find gibbon characteristics that can be compared in any meaningful way with those of potential outgroups. This problem is shared by all available data sets. The tempo of evolutionary change, however, appears to differ among the data sets, similar to DNA sequences derived from different parts of the genome. Most data from set one appear to have changed considerably less than most of those from set three, whereas set two yields an intermediate position. As a result, each set appears to be suited to the analysis of different levels of resolution within the hylobatid radiation, but it is vocal data that produce the most reliable phylogeny of the data sets under study.

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