It has been hypothesized that mandibular corpus morphology of primates is related to the material properties of the foods that they chew. However, chewing foods with different material properties is accompanied by low levels of variation in mandibular strain patterns in macaques. We hypothesized that if variation in primate mandible form reflects adaptations to feeding on foods with different material and geometric properties, then this variation will be driven primarily by differences in oral food processing behavior rather than differences in chewing per se. To test this hypothesis, we recorded in vivo bone strain data from the lateral and medial surfaces of the mandibular corpus during complete feeding sequences in three adult male Sapajus as they fed on foods with a range of sizes and material properties. We assessed whether variation in mandibular corpus strain regimes is associated with variation in feeding behaviors and/or chewing on different foods, and we quantified the relative variation in mandibular corpus strain regimes associated with chewing on foods of different material properties versus a range of oral food processing behaviors (incisor, premolar, and molar biting; pulling on incisors; mastication). Feeding behavior had a significant effect on mandibular corpus strain regimes, as did chewing side and the cycle number in a feeding sequence. However, food type had weaker effects and usually only through interaction effects with chewing side and/or cycle type. Strain regimes varied most across different chew sides, then across different behaviors, and lastly between mastication cycles on different foods. Strain magnitudes associated with premolar, molar, and incisor biting were larger than those recorded during mastication. These data suggest that intra- and inter-specific variation in mandible morphology is a trade-off between performance requirements of different oral food processing behaviors and of variation in chewing side, with direct effects of food type being less important.
Bibliographical noteFunding Information:
We thank E. Vogel, N. Yamashita, and B. Wright for the opportunity to present this paper in their symposium Food materials testing and its relevance for primate biology , held at the 2013 Annual Meeting of the American Association of Physical Anthropologists, and for their invitation to contribute to this volume. We thank the staff of the ARC at The University of Chicago for their animal care and expertise and the reviewers of the paper for their feedback. This work was funded by National Science Foundation HOMINID and Physical Anthropology grants ( BCS 0240865 ; BCS 0504685 ; BCS 0725126 ; BCS 0725147 ; BCS 0962682 ).
- Capuchin monkeys
- Feeding ecology
- Mandibular biomechanics