Chatterjee, Helen Jane; (2001) Phylogeny and Biogeography of Gibbons, Genus Hylobates. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

This thesis aims to reconstruct the phylogenetic and biogeographic history of gibbons, genus Hylobates. Phylogenetic relationships among gibbons are controversial. This study uses molecular and morphological data to resolve some of these controversies, and provides a new phylogeny for the genus. The estimate of gibbon phylogeny is combined with distribution data to reconstruct the biogeographic history of gibbons. In the first part of the study, original mitochondrial control region sequence data and published cytochrome b gene sequence data are analysed using maximum likelihood, parsimony and bootstrapping methods. Results of these analyses indicate a gibbon phylogeny which shows the following subgeneric relationships: Nomascus, Symphalangus and Bunopithecus are successively more closely related to Hylobates. A molecular clock is employed which suggests that the gibbon radiation dates to about 10.5 million years ago (Ma). In the second part of the study, craniodental and postcranial metric variables are analysed using multivariate statistical methods to investigate interspecific morphological variability. Multivariate statistical analyses across the gibbon skeleton show that the eleven currently recognised species form five distinct morphological groups. The metric data are further employed to investigate phylogenetic interrelationships among gibbons. These data are converted into discrete character states using segment and range coding. The re-coded data are analysed using parsimony and bootstrapping methods. These analyses indicate that gibbon skeletal metric data is phylogenetically uninformative at the species or subgenus level. In the third part of the study, three alternative methods of biogeographic reconstruction are employed: ancestral area analysis using irreversible parsimony, ancestral area analysis using reversible parsimony and dispersal-vicariance analysis (DIVA). Results of the DIVA analysis are combined with estimates of divergence dates, to propose a new pattern of radiation for the genus Hylobates. This analysis indicates that the gibbon radiation may have begun in Indochina around 10.5 Ma. Between 10.5 and 8.6 Ma gibbons radiated southwards to Sumatra. Subsequently, they differentiated into two types of gibbon on Sumatra, representing the subgenera Symphalangus and Hylobates. A third radiation approximately 7-8 Ma saw the dispersal of Bunopithecus into Burma, Assam, and Bangladesh. At around 3-5 Ma there was a second radiation of subgenus Hylobates, involving dispersal onto the islands of Borneo, Mentawai and Java. Between 0.3 and 1.8 Ma taxa in the subgenus Nomascus differentiated into Cambodia and Hainan Island. This study provides a novel reconstruction of the historical biogeography of gibbons. In addition, parsimony and likelihood analyses of molecular and morphological data sheds light on the controversial topic of hylobatid phylogeny.

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