Maxillary tooth size variability and influence of hypodontia in the Suncus murinus

Dry cranila specimens from 184 Suncus murinus from the wild Nagasaki (normal dentition) population and laboratory strains of KAT (normal dentition), NAG (missing I 3) and TESS (missing P 3) were examined to quantify the relationship between size variation and the influence of tooth absence in maxillary dentition. We first measured and analyzed maxillary tooth size variability in normal S. murinus based on the coefficient of variation (CV). Molariform teeth showed lower CVs, whereas unicuspid teeth showed relatively high CVs in shrews with normal dentitions. In this species, molariform teeth have complex cusps and clear ridges, whereas unicuspid teeth have no occlusal surface. In particular, I 3 and P 3 had relatively high CVs, and these teeth were commonly absent. We also examined the relationship between tooth size and number in this species. Individuals missing I 3, namely, NAG strain, had lower P 3 CVs than the normal group. However, those missing P 3 had higher I 3 CVs than other teeth and the normal group. These results suggest that tooth disappearance does not always lead to stability of other teeth. The variability in tooth size appears to be influenced not only by functional and developmental factors but also by phylogenetic backgrounds and factors regulating tooth formation.