Feeding systems are the energy-acquiring systems of humans and other primates. The teeth, jaws, and muscles, are the proximal interface between primates and their environments. Therefore, understanding the evolutionary forces that shape those components is essential to understanding the adaptation and evolution of primates. This work tests hypotheses and models relating diversity in the primate feeding system to size-related changes in food intake rate. It documents how shape and movements of the mandible, the size and architecture of the jaw muscles, and the amount of food an animal eats in a single bite change with body size to meet size-required changes in food intake rate of primates. These data will be collected using computed tomography (CT) scanning of primate mandibles, anatomical studies of primate chewing muscles, and behavioral studies of primates feeding in captivity. Mathematical models of the feeding system will be tested, modified and improved, then used to examine how feeding system designs in different evolutionary groups of primates balance trade-offs between advantages of bite force production, chewing speed and gape.
This research will create novel and important data sets that can be accessed in the future by other researchers interested in feeding biomechanics, bone biomechanics, and musculoskeletal systems in general. The investigators will continue to recruit under-represented minority and female undergraduates to receive training and mentoring in research and advice on their paths to graduate, medical, and other professional schools. These students will collaborate in all aspects of the work, including presentation and publication. The PIs will continue their outreach programs to local schools and their synergistic activities with other NSF-funded projects.
Our goal was to gain a better understanding of the bite sizes used by anthropoid primates (monkeys and apes). We tested this in a zoo setting (The Philadelphia Zoo) on twelve species of anthropoids ranging in size from 100g pygmy marmosets to 15kg mangabeys, and on a range of foods from soft banana to hard raw beets. The purpose of the study was to assess the degree to which bite size keeps pace with body size, the basic assumption being that larger primates take larger bites. Any deviation from this pattern has implications for how animals must process their foods to obtain sufficient energy to support their metabolic needs. This study dovetails with a past project we did on lemurs and lorises (primitive primates called strepsirrhines) at the Duke Lemur Center. In the present study, we found that bite size does keep pace with body size in anthropoid primates, at least for very stiff foods (e.g., carrots, sweet potato, beets). For pliant foods (most soft fruit), the pattern is less clear. We also found that anthropoids tend to take smaller bites at all body sizes compared to strepsirrhines. This is likely related to face proportions; anthropoids tend to have shorter faces overall compared to strepsirrhines. Furthermore, one group of strepsirrhines that have short faces (the leaf-eating indriids) plots with the anthropoids in taking small bites. The results of this study have several implications for understanding food processing and foraging time in primates. Future work will focus on studying these patterns in the wild. Image 1: Kibar, a spectacled langur, working on a sweet potato. Image 2: Andrew, a squirrel monkey, tipping his head back to eat an apple. Image 3: Results for pliant foods. Reduced major axis regressions of Log Vb (bite size - cm2) against Log Body Mass (g) for anthropoids (filled shapes) and strepsirrhines (open shapes). For pliant foods, there is a significant difference between slopes (p=0.001) and y-intercepts (p<0.0001) when anthropoids are compared to strepsirrhines. Fruit eaters are represented by circles, insect eaters by crosses, gum eaters by minuses, and leaf eaters by triangles. Image 4: Results for stiff foods. Reduced major axis regressions of Log Vb (bite size - cm2) against Log Body Mass (g) for anthropoids (filled shapes) and strepsirrhines (open shapes). For stiff foods, only the y-intercept is significantly different (p<0.0001). Fruit eaters are represented by circles, insect eaters by crosses, gum eaters by minuses, and leaf eaters by triangles.
