1Department of Biological Sciences, Dartmouth College, 2Institute of Human Origins, School of Human Evolution and Social Change, Arizona State University, 3Institute of Animal Physiology, Physiological Chemistry and Animal Nutrition, University of Munich, 4Division of Zoo Animals, Exotic Pets and Wildlife, Vetsuisse Faculty, University of Zurich, 5Department of Anthropology, California State University Fullerton, 6Department of Anthropology, Dartmouth College
Thursday 7, 200DE
Numerous studies have shown that primates generally avoid hard and tough foods when possible. Hard foods can cause catastrophic damage to the dentition, while tough foods might be fractured less effectively, reducing nutritional input during digestion. Consequently, the notion that the primate dentition is adapted to crack and/or tear mechanically challenging fallback foods has received much support from recent behavioral and morphological studies. Here we explore the mechanistic basis of particle breakdown by examining the relationship between dietary toughness, dental macro-wear, and chewing efficiency (as measured by fecal particle size) across wet and dry seasons in a sample (n=11) of wild geladas (Theropithecus gelada) from an ecologically-intact Afroalpine grassland in northern Ethiopia. A matched-pairs t-test revealed that mean fecal particle size (MPS) was significantly higher during the dry season (t=-8.0225, df=10, P<0.0001), indicating that individuals chew food less efficiently during this time. The difference corresponds to a shift from habitual short grass consumption during the wet season to consumption of underground storage organs and other vegetation with challenging mechanical properties during the dry season. MPS for older individuals is higher than expected on the basis of body size alone, implicating dental senescence as a contributing factor. Indeed, values for M2 relief index and shearing crest length were lowest in older individuals. These results support the long-held assumption that the dental morphology of the Theropithecus clade is associated with consumption of tough foods. The relationship between differential chewing efficiency and seasonal body conditions and mortality rates is discussed.
This research was supported in part by an NSF Graduate Research Fellowship, the Claire Garber Goodman Fund from the Department of Anthropology at Dartmouth College, and a fellowship from the Institute of Human Origins at Arizona State University.