Chewing rates among domestic dog breeds

Abstract

SUMMARYThe mammalian masticatory rhythm is produced by a brainstem timing network. The rhythm is relatively fixed within individual animals but scales allometrically with body mass (M b ) across species. It has been hypothesized that sensory feedback and feedforward adjust the rhythm to match the jaw's natural resonance frequency, with allometric scaling being an observable consequence. However, studies performed with adult animals show that the rhythm is not affected by jaw mass manipulations, indicating that either developmental or evolutionary mechanisms are required for allometry to become manifest. The present study was performed to tease out the relative effects of development versus natural selection on chewing rate allometry. Thirtyone dog breeds and 31 mass-matched non-domestic mammalian species with a range in M b from ~2kg to 50kg were studied. Results demonstrated that the chewing rhythm did not scale with M b among dog breeds (R0.299, P>0.10) or with jaw length (L j ) (R0.328, P>0.05). However, there was a significant relationship between the chewing rhythm and M b among the non-domestic mammals (R0.634, P<0.001). These results indicate that scaling is not necessary in the adult animal. We conclude that the central timing network and related sensorimotor systems may be necessary for rhythm generation but they do not explain the 1/3rd to 1/4th allometric scaling observed among adult mammals. The rhythm of the timing network is either adjusted to the physical parameters of the jaw system during early development only, is genetically determined independently of the jaw system or is uniquely hard-wired among dogs and laboratory rodents.

Intraspecific scaling of chewing cycle duration in three species of domestic ungulates

“…They showed that, within dogs, CCD scales with body mass 0.07 and jaw length 0.20 , but that there is no correlation between the CCD and either of the morphological variables. Because a non-canid sample matching the sizes of the individual dog breeds yields scaling exponents similar to those obtained from previous interspecific studies, Gerstner and colleagues (Gerstner et al, 2010) propose that the limited size range sampled among the dogs is not a confounding factor in the analysis. More importantly, they argue that the lack of correlation between body size and CCD has a developmental basis.…”

“…Small animals chew at a higher frequency and thus have a shorter chewing cycle duration (CCD) than larger animals (Druzinsky, 1993;Fortelius, 1985;Gerstner et al, 2010;Gerstner and Gerstein, 2008;Ross et al, 2010;Ross et al, 2009a;Ross et al, 2009b;Shipley et al, 1994). Several explanations have been proposed for the observed scaling of CCD with body mass and jaw length.…”

“…With respect to body mass, the observed scaling of CCD is typically related to scaling relationships between basal metabolic rate, tooth size and the volume of food comminuted per chew, which would ultimately predict that CCD scales with body mass 0.25 (see Fortelius, 1985;Kay, 1985;Ross et al, 2009b). Most observations of the scaling of CCD and body mass provide slopes slightly lower than this predicted value, although the range of reported slopesfrom 0.13 to 0.28 depending on the data set -is quite large (Druzinsky, 1993;Fortelius, 1985;Gerstner et al, 2010;Gerstner and Gerstein, 2008;Ross et al, 2010;Ross et al, 2009a;Ross et al, 2009b;Shipley et al, 1994). Notably, strepsirrhine primates exhibit a decrease in CCD with body mass (i.e.…”

“…However, domesticated species bred for different body sizes offer one potential avenue for exploring the issues of the scaling of CCD. Recently, Gerstner and colleagues (Gerstner et al, 2010) utilized the domestic dog in one such study, sampling CCD in breeds ranging in body mass from 2kg to 50kg. They showed that, within dogs, CCD scales with body mass 0.07 and jaw length 0.20 , but that there is no correlation between the CCD and either of the morphological variables.…”

“…Specifically, early changes in CCD within an individual may occur because of changes in jaw mass that elicit a response from immature neural networks underlying the CPG. However, once the CPG controlling masticatory rhythm has matured, an individual's CCD can no longer increase with additional growth (Gerstner et al, 2010). There are two lines of evidence to support this hypothesis.…”