Morphotypical variability of the chewing surface of the M3 tooth Myodes rutilus Pallas, 1779 (Arvicolinae, Rodentia) in the Middle Ob area of the Tyumen region

In this paper we present the results of the studies of the morphotypic variability of the molars Myodes rutilus of the Middle Ob, Tyumen region. The morphotypes of the M3tooth of the red vole characteristic of the subzone of the middle taiga of Tyumen region were revealed. The age variability of the structure of the chewing surface of the M3tooth of the red vole was traced. In the group of wintering individuals there was a significant increase in the proportion of morphotypes of medium complexity with a significant decrease in the proportion of complex morphotypes. The complexity coefficient of the M3tooth of wintering red vole individuals is significantly lower than that of this-year brood. Simplification of the structure of the M3tooth in the red vole as the age increasing is associated with the grinding of the tooth prism during life. For the red vole of the Middle Ob area, a change in the occurrence of M3 tooth motphotypes during population cycles was revealed. It was noted that the occurrence of morphotypes of medium complexity at all phases of the population cycle were relatively stable, and the decrease in the relative abundance of the red vole was accompanied by a significant increase in the occurrence of simple morphotypes. Population peaks are characterized by a decrease in the occurrence of simple morphotypes. Probably, simple morphotypes have an adaptive value for the red vole population in the period with a low relative abundance of the species at a stable frequency of occurrence of morphotypes of medium complexity. The influence of biotopic characteristics of red vole habitats on the M3tooth structure was also noted. In the most favorable living conditions, the structure of the chewing surface is characterized by less complexity, but in less favorable conditions there is a tendency to complicate the structure of the tooth.