142 - Examining the Relationship Between Inferior Alveolar Nerve Volume and Dietary Properties in Primates

Poster Board Number: 142
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Abstract Body : Tooth shape is thought to generally correlate with food material properties, causing many researchers to categorize primate diets into non-resistant foods (fruit, gums) and resistant foods (leaves, seeds, grass, insects) that each require a different tooth shape to efficiently break down foodstuffs. Although teeth are the body’s interface with the external environment, all food material properties are tested via nervous sensation provided by the superior and inferior alveolar nerves (IAN) – terminal branches of the trigeminal nerve (CNV). While we understand that primates extensively test the material properties of food on the dentition, no study has addressed whether there is a relationship between the size of the nervous tissues needed for sensation and the diet that a primate eats.

We used 66 individuals (23 females, 33 males, 8 unknown) from 31 primate species and 3 mammalian outgroups (Lontra canadensis (n=1), Rattus norvegicus (n=5), and Oryctolagus cuniculus (n=4)) for our analyses. Using iodine staining techniques (diceCT), the IANs were digitally segmented from both the left and right sides of the mandible and a total volume was established. Diet was established from the primary literature using traditional categories (e.g., frugivore, folivore) or resistant vs. non-resistant based on average percentages of foods eaten by species. Phylogenetic ANOVAs, PGLS (phylogenetic generalized least squares analyses), and multiple regressions were used to examine the relationship between IAN volume, diet, and mandible length.

PhylANOVAs established no significant relationships between IAN volumes and either food category (p = 0.925) or resistance (0.777) after mandible size was adjusted for. Additionally, the phylogenetic multiple regressions showed no significant relationship between the dietary categories and IAN volume (p = 0.416, R2 = 0.325). PGLS analyses showed that there is a significant and isometric relationship between IAN volume and mandibular length (p < 0.001; R2 = 0.967).

These results indicate that nervous tissue size is not significantly related to the traditional dietary categories that primates are often placed in and are thus not likely under the same evolutionary pressures as the teeth to change shape in response to a change in overall species diet. Overall, the total volume of the IAN is much more tightly correlated to mandible size – and likely body size by extension – a trend that is shown in previous research on relationships between nervous tissue volume and body size. This indicates overall that the nervous tissues within primate oral structures are sensitive enough to accommodate all food categories and that no specialized nervous structures are required.