Dental Variation in an Invasive Species at the Dispersal Stage: Microtus rossiaemeridionalis (Arvicolinae, Rodentia) in Irkutsk Oblast, Southern Cis-Baikal Region.

The East European vole is a facultative synanthropic species that actively spreads in the eastern part of northern Eurasia. The distribution area of the species in Irkutsk oblast has been known as a disjunct part of the range since the 1980s. Our dataset includes 98 individuals caught in 2016–2017 and 2021–2023 in the eastern segment of the species'dispersal area, where the East European vole was first discovered in the early 2010s. Animals were caught in anthropogenically transformed landscapes spanning from the outskirts of Irkutsk to kilometer 23 of the Goloustnenskii Tract; trapping in natural biotopes revealed no M. rossiaemeridionalis. Species identification was based on molecular genetic markers. Morphological and fine structural characteristics of molar teeth were studied using both light and scanning electron microscopy. The complexity of the occlusal surface, the alternation patterns of the enamel cutting edges (occlusal regularity), and the presence or absence of atypical extra elements such as prismatic folds and prisms in places of the early cricetid dental features were assessed. The estimates of the complexity and regularity patterns fell within the range of dental variability known for the continuous distribution area of the species. The atypical extra elements on molars were described in M. rossiaemeridionalis for the first time based on material coming from two trapping sites. With the maximum manifestation of these folds, a supernumerary prism, topologically corresponding to the hypoconid, is separated from the posterior lobe of the lower teeth. The distribution of lamellar and radial enamel on the supernumerary prism is not consistent with the functionally significant and evolutionarily determined distribution of enamel types on teeth of the genus Microtus. It is concluded that the studied local micropopulation exhibits the phenotypic consequences of population restoration from a small number of founders. Apparently, the species in the study area faces multiple successive cases of establishment (naturalization) in a new territory. The results obtained confirm the prospects of using dental characters for monitoring Arvicolinae species, the distribution boundaries of which are subject to significant spatial changes in the relatively short periods of time available for observation. [ABSTRACT FROM AUTHOR]