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


Male bi-maturism and the costs of reproduction in wild Bornean orangutans

CHERYL D. KNOTT1 and MELISSA EMERY THOMPSON2.

1Anthropology, Boston University, 2Anthropology, University of New Mexico

Friday 10:30-10:45, Ballroom A Add to calendar

The existence of two, truly distinct, male reproductive morphs may be a unique mammalian feature of orangutans. Flanged males are twice the size of females and have well developed secondary sexual characteristics, whereas the unflanged males retain a smaller, sub-adult or female-like body size and lack secondary sexual features. Both male morphs are sexually mature and have sired offspring in the wild and captivity. Once a male has transitioned into the flanged form, the change is irreversible. Here we use nearly 20 years of data on energetic variables to compare the relative costs of reproduction in wild male orangutans (Pongo pygmaeus wurmbii) from Gunung Palung National Park, Indonesian Borneo. Data are presented on energy intake, energy expenditure, ranging patterns, and mating behavior in these two morphs. The physiological effects of these energetic and social behaviors are assessed through measurement of testosterone, cortisol, C-peptide, and ketones from non-invasively collected urine samples. Data demonstrate the significantly higher cost of being a prime flanged male orangutan. Maintaining the flanged male morphology and associated behaviors leads to increased energetic demands compared to the unflanged state. We also differentiate a third class of adult male - the past prime flanged male. These data are used to propose a new explanation for how the energetic demands of being a prime flanged male orangutan, coupled with the distinctive features of the Southeast Asian rain forest and long inter-birth intervals in females, selected for the flanged and unflanged morphological forms, with their differing reproductive and life history strategies.

We thank our primary supporters: National Science Foundation (Grant #0936199); National Geographic Society; Leakey Foundation; Wenner-Gren Foundation; US Fish and Wildlife Service; Orangutan Conservancy; Conservation, Food and Health Foundation.

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