Behaviour 2019
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Episodes of fruit scarcity are associated with muscle wasting in wild Bornean orangutans
Caitlin A. O'Connell1, Andrea L. DiGiorgio2,1, Alexa D. Ugarte1,3, Rebecca S.A. Brittain1, Daniel J. Naumenko4, Sri Suci Utami Atmoko5, Erin R. Vogel1. 1Rutgers University, New Brunswick, New Jersey, United States; 2Princeton University, Princeton, New Jersey, United States; 3New York University, New York, New York, United States; 4University of Colorado Boulder, Boulder, Colorado, United States; 5Universitas Nasional, Jakarta, Jakarta Raya, Indonesia

Animals have evolved a vast array of strategies to cope with seasonality but may still experience deficits in meeting their energy requirements. Wild Bornean orangutans face pronounced low fruit periods, and experience negative energy and protein balance during these times. Given the severity and unpredictability of fruiting, we examined the possibility that wild orangutans experience muscle wasting during low fruit periods at Tuanan Research Station in Central Kalimantan, Indonesia. Utilizing a method that was validated in wild chimpanzees, we use urinary creatinine standardized by specific gravity as a non-invasive measure of muscle mass to compare flanged males (N=31), unflanged males (N=15), adult females (N=32), and immature orangutans (N=22) during high and low fruit periods. Episodes of fruit scarcity were associated with significantly lower muscle mass compared to high fruit periods for all age-sex classes (F(5.094)=13.6, p< 0.001). These findings add to growing evidence that orangutans are characterized by unique metabolic plasticity shaped by their environment and highlight the precarity of remaining populations in the face of rapid habitat destruction and climate change.