Abstract # 114:

Scheduled for Sunday, September 18, 2011 09:45 AM-10:00 AM: Session 16 (Salon F (Sixth Floor)) Oral Presentation


E. R. Vogel1,2, C. D. Knott3, B. E. Crowley4, M. D. Blakely5, M. D. Larsen1 and N. J. Dominy6
1The George Washington University, Center for the Advances Study of Hominid Paleobiology, Department of Anthropology, 2110 G Street NW, Washington, DC 20052, USA, 2Rutgers University, 3Boston University, 4University of Toronto, 5University of California Santa Cruz, 6Dartmouth College
     The rainforests of Borneo are often viewed as impoverished habitats for vertebrate frugivores. For the largest canopy-dwelling frugivore, the orangutan (Pongo pygmaeus), the evolution of extreme hypometabolism is a testament to its marginal existence. Yet Bornean orangutans still experience energy deficits during prolonged periods of fruit scarcity. Such findings suggest that orangutans might also endure somatic catabolism when fruit is scarce. To test this hypothesis, we conducted the first study of protein cycling in a wild primate by analyzing urinary catabolites and nitrogen stable isotopes from 27 individuals. We quantified urea concentration using a diacetylmonoxime method and ?15N and %N weight using an elemental analyzer. Urea concentration decreased with decreasing fruit abundance (p=0.003), indicative of nitrogen recycling from urea during episodes of fruit scarcity. This decrease corresponded with decreased protein intake (p<0.05). However, orangutans avoided falling into a negative protein balance state of tissue wasting, as evidenced by stable ?15N and %N across varying fruit availability levels. During episodes of fruit scarcity, orangutans shifted to a diet of tough fallback foods, with a mean daily intake of 1.4 g protein kg-1 metabolic mass. Such values are inadequate for humans and one-tenth the intake of mountain gorillas, yet they appear sufficient for orangutans. Our findings show that orangutans averted tissue wasting, and highlight the value of their unusual metabolic and craniodental adaptations to avoid protein imbalance.