The 82nd Annual Meeting of the American Association of Physical Anthropologists (2013)

Patterns of sexual dimorphism in Pan and Gorilla limb bones


Department of Biology, Saint Mary's College of California

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While it is well-established that Pan and Gorilla differ in degree of size-based sexual dimorphism, less is known about their patterns of shape-based sexual dimorphism in the postcranium or about geographic variation in these patterns. Using a geographically diverse sample, differences between the genera in patterns of sexual dimorphism in the limb bones were investigated.

Forty-three linear measurements of ten limb bones were collected from Gorilla (n=266) and Pan (n=274) adults, size-corrected using geometric means, and analyzed using t-tests and principal components analyses (PCAs). Male and female Gorilla are best separated on PC2 and PC3, with high loadings for size-corrected lengths and midshaft widths and low loadings for size-corrected measurements of the proximal and distal ends. Pan sexes are not as strongly distinguished but are best separated on PC1 and PC2, on which size-corrected lengths, hand and foot bone widths, and elbow and knee measurements load most heavily. T-tests and PCAs of size-corrected measurements show greater shape differences between sexes in Gorilla than in Pan.

Examination of PCA plots by species, subspecies, and population, however, show that patterns of sexual dimorphism differ at each of these levels and do not simply reflect the genus-level pattern. For example, in Gorilla, the female distribution pattern varies among populations. In Pan, P. troglodytes troglodytes and P. t. verus display some separation of sexes, while little sexual dimorphism is apparent in the distributions of P. t. schweinfurthii and P. paniscus. Patterns of shape-based sexual dimorphism in limb bones exhibit geographic variation within each genus.

This study was supported by the Saint Mary’s College of California School of Science Summer Research Program and Faculty Development Fund, The Wenner-Gren Foundation, The Leakey Foundation, Sigma Xi, City University of New York, and New York Consortium in Evolutionary Primatology.

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