The 81st Annual Meeting of the American Association of Physical Anthropologists (2012)

Variation in hair cortisol in wild anubis and hamadryas baboons and their natural hybrids


1Department of Anthropology, The George Washington University, 2Department of Anatomy and Neurobiology,, Washington University School of Medicine, 3Department of Anthropology, New York University, 4Center for Species Survival, Smithsonian Conservation Biology Institute

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Cross-specific differences in endocrine function have been observed among primates, and may be related to variation in social environments and reproductive strategies. We examined cortisol levels in hair samples (n=716) from male and female anubis (Papio anubis ), hamadryas ( P. hamadryas) and hybrid baboons of the Awash National Park to see whether a) there were ontogenetic differences in adrenocortical function and b) signs of the effects of severe drought. Anubis baboons tend to have lower hair cortisol concentrations than hamadryas and hybrid baboons. Moreover, analysis of external phenotype in hybrids finds a correlation between a more anubis-like appearance and cortisol levels, suggesting a biological basis for inter-specific differences independent of social environment. Ontogeny of adrenocortical function reflected differences in life-history trajectories, with hamadryas and hybrids showing a more precocial increase in cortisol coincident with testicular development. Comparisons of drought and non-drought samples suggest a blunting in adrenocortical function in male and female anubis, hamadryas and hybrid baboons under severe chronic ecological stress. Overall female hair cortisol concentrations were significantly higher compared to males independent of rainfall. However, examination of species specific sex differences showed that anubis females did not differ from anubis males under non-drought conditions; under drought conditions anubis females had significantly higher hair cortisol concentrations compared to males. Hybrids exhibited the reverse pattern compared to anubis baboons under both non-drought, and drought conditions. These results demonstrate species and sex specific differences in stress biology, which have implications for understanding reproductive and life history tradeoffs in primates.

Hair samples collected during fieldwork supported by the Earthwatch Institute, New York University, Washington University, the Harry Frank Guggenheim Foundation, and the National Science Foundation. Analysis carried out with the support from the Lewis Cotlow Fund (2008 and 2010) and the National Science Foundation Integrative Graduate Education and Research Traineeship award (NSF IGERT – Award ID: 0801634).

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