Genetic and Environmental Control on Mandibular Form and Function in Mice

Abstract

Bone modelling and remodelling is a means by which organisms may be able to plastically modify the external morphology and internal structure of their skeletal tissues. We have shown previously that lab mice of the C56BL/6 strain that were fed either hard or soft foodstuffs with the same nutritional value have significantly different shaped jaws. The shape differences manifest as difference in function, with the mandibles of hard food eaters possessing a higher mechanical advantage (MA) of the temporalis and masseter adductor musculature than the soft food eaters. Here we compare the magnitude of difference in MA between the C56BL/6 hard and soft food eaters to the difference in MA between C56BL/6 hard food eaters and BALB/c hard food eaters. We also compare the difference between strains and between plastically generated morphotypes in resistance to bending and torsion from second moment of area measurements from CT scans and in simulated functional bony stress and strain deduced from finite element models. Hard food eaters have increased resistance to bending, torsion (n=39) and loading induced stress and strain (n=4) compared to soft food eaters. C56BL/6 and BALB/c mice have significantly different shaped jaws with BALB/c mice having more gracile jaws with a less developed masseteric ridge (n = 20). Comparative finite element (FE) models show that BABL/c mice also experience consistently greater deformation when subject to functional feeding‐induced loads (n=4). Environmentally driven plasticity leads to functional differences that favour the efficiency of food processing in the hard food eaters. Difference in performance between hard and soft food eaters exceed the difference in performance between lab strains, suggesting plasticity as a mechanism to provide morphological variation on which natural selection may act.