Primate dietary ecology in the context of food mechanical properties.

Substantial variation exists in the mechanical properties of foods consumed by primate species. This variation is known to influence food selection and ingestion among non-human primates, yet no large-scale comparative study has examined the relationships between food mechanical properties and feeding strategies. Here, we present comparative data on the Young's modulus and fracture toughness of natural foods in the diets of 31 primate species. We use these data to examine the relationships between food mechanical properties and dietary quality, body mass, and feeding time. We also examine the relationship between food mechanical properties and categorical concepts of diet that are often used to infer food mechanical properties. We found that traditional dietary categories, such as folivory and frugivory, did not faithfully track food mechanical properties. Additionally, our estimate of dietary quality was not significantly correlated with either toughness or Young's modulus. We found a complex relationship among food mechanical properties, body mass, and feeding time, with a potential interaction between median toughness and body mass. The relationship between mean toughness and feeding time is straightforward: feeding time increases as toughness increases. However, when considering median toughness, the relationship with feeding time may depend upon body mass, such that smaller primates increase their feeding time in response to an increase in median dietary toughness, whereas larger primates may feed for shorter periods of time as toughness increases. Our results emphasize the need for additional studies quantifying the mechanical and chemical properties of primate diets so that they may be meaningfully compared to research on feeding behavior and jaw morphology.

Trabecular Anisotropy in the Primate Mandibular Condyle Is Associated with Dietary Toughness.

Past attempts to establish a relationship between mandibular morphology and different dietary categories (e.g., frugivore, folivore, insectivore) have had mixed results, possibly because descriptive dietary categories are too broad and obscure variation within primate diets. Another potential reason is that not all aspects of skeletal architecture, especially trabecular anisotropy, have factored into functional assessments of dietary inputs into jaw form. Recent emphasis on quantifying food mechanical properties (FMPs) has provided an alternative to reliance on dietary categories. We used data on FMPs to test for correlations among dietary toughness and Young's modulus and the trabecular structure of the mandibular condyle, which is loaded during feeding and should reflect differences in masticatory stresses associated with different dietary FMPs. Adult primate mandibles from 11 species were imaged using high-resolution X-ray computed tomography, and trabecular structure was analyzed with BoneJ and Quant3D to assess common three-dimensional trabecular parameters. Results of phylogenetic generalized least squares analysis suggested a positive correlation between the degree of anisotropy (DA) and toughness, and weaker correlations between FMPs and various other trabecular variables. Because the DA contributes to the mechanical properties of bone, these results suggest a functional relationship between dietary toughness and trabecular anisotropy in the mandibular condyle. Such a perspective underscores the need to consider all aspects of skeletal morphology in evaluating the links between diet and jaw biomechanics. Anat Rec, 2018. © 2018 Wiley Periodicals, Inc.