Growth and reproduction in island and mainland populations of the vole Microtus epiroticus

Abstract

The vole Microtus epiroticus was accidentally introduced from Russia to the high arctic archipelago of Svalbard between 30 and 70 years ago. Data on growth patterns were collected in the laboratory for animals originating from the unique Svalbard population and from a population in Finland, close to northern Russia. Gestation period, birth mass, litter size, and age at first reproduction were similar in both populations. Longitudinal growth data were analyzed using polynomial growth curve models. Growth was bimodal, with an early peak at 8–10 days and a later peak at 15 days. The Finnish animals differed from the Svalbard animals by a higher growth rate at 12–15 days. In the field, adult body masses were much greater on Svalbard than in Finland. This difference might have been due to a phenotypic response to the cold arctic climate. We discuss the lack of clear predictions regarding microtine adaptation to the unpredictable arctic environment, and emphasize that in terms of high reproductive rates in mammals, M. epiroticus represents an extreme case.