Meeting Abstract

P1.48  Sunday, Jan. 4  Chewing Rate Allometry Requires Natural Selection GERSTNER, GE; University of Michigan geger@umich.edu

Mammalian chewing is produced by brainstem circuits called central pattern generators, which can be functionally subdivided into burst-generating neurons and a central timing network (CTN). The CTN generates a rhythm that sets chewing rate. Chewing rate scales allometrically to body mass, and it is generally assumed that feedback and feedforward systems adjust chewing rate to match the jaws natural resonance frequency. However, studies have shown that oral motor rhythms are unaffected by experimentally increasing jaw mass. But these studies were not specifically designed to explore chewing rate scaling, and none involved determining whether chewing rate required developmental time scales to adapt to experimentally increased jaw mass. Therefore, we studied chewing rate and body mass relationships among 20 dog breeds, ranging in size from 3.6 kg (beagle) to 68 kg (Newfoundland) and 20 matched wild mammalian species. Chew duration was not significantly correlated with body mass among dog breeds (p = 0.418, r² = 0.023). By contrast, a significant correlation between body mass and chew duration was found among the 20 mammalian species (p = 0.002, r² = 0.284). Next, canine jaw masses were estimated by taking the product of body mass and the ratio of head length to body length. Estimated jaw mass was also not significantly correlated with chew duration among the dog breeds (p = 0.627, r² = 0.008). The results suggest that chewing rate allometry requires natural selection; neural feedback and feedforward mechanisms alone do not necessarily guarantee the allometric relationship. The results demonstrate that, at least among domestic dog breeds, relaxed selection pressure can greatly reduce the allometric scaling relationship, which may have significant implications for neuromotor, biomechanical, functional morphological, ethological and ecological investigations.