Effects of diet quality on the musculoskeletal system of the masticatory apparatus in <i>Mus musculus domesticus</i>

Isolated environments such as islands can provide restricted dietary resources of varying quality. This has a major impact on evolution of island species, and can lead to rapid morphological adaptation, especially in small mammals. To understand the impact of diet quality on the masticatory apparatus in the model species Mus musculus domesticus, we quantitatively analysed the main masticatory muscles and the mandibular morphology in semi-natural populations kept on different diets for six generations. The investigation of individuals of the F5 generation raised on high quality (HQ) or standard quality (SQ) diets revealed significantly higher muscle mass and larger anatomical cross-sectional area (ACSA) of the m. masseter and the m. temporalis in mice raised on the SQ diet as compared with the HQ diet. A trend towards more robust (i.e. sturdy) mandible morphology in SQ mice as compared with HQ mice was evident. The investigation of individuals of two F6 generations that were fed on a diet different from that of the preceding generation revealed that the diet switch from HQ to SQ resulted in increased muscle size, whereas the diet switch from SQ to HQ lead to decreased muscle size as compared with the respective control group. The mandible displayed limited differences in morphology. These findings suggest that within six generations, diet quality could be a selection factor for morphological traits in the mandible that may become epigenetically fixed. However, additional studies such as DNA methylation and histone modification are necessary to unravel the role of the epigenome in this context.