Inheritance and selective effects of color phase in white-handed gibbons (Hylobates lar) in central Thailand

Abstract

The white-handed gibbon Hylobates lar (Hylobatidae) is polymorphic for pelage coloration throughout its range. The frequencies of the two color phases, brownish-black and buff, and their pattern of inheritance, are reported in a sample of 64 wild social groups and in an additional sample of newborn individuals, in Khao Yai National Park, east-central Thailand. The total sample of 318 individuals is half dark and half light phase. Color is not correlated with sex or age class. Data on parent and offspring coloration are consistent with simple Mendelian inheritance in which dark is controlled by a dominant allele. The monogamous adult pair combinations are random with respect to color, contrary to some previous reports. No evidence was found for any selection based on color; there were no differences in numbers of offspring or group size among different adult pair color combinations. Whether this polymorphism is maintained by balancing selection is unclear; several plausible mechanisms are discussed.