GROWTH AND REPRODUCTION IN ISLAND AND MAINLAND POPULATIONS OF THE VOLE MICROTUS-EPIROTICUS

The vole Microtus epiroticus was accidentally introduced from Russia t o 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, li tter size, and age at first reproduction were similar in both populati ons. Longitudinal growth data were analyzed using polynomial growth cu rve 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 bod y masses were much greater on Svalbard than in Finland. This differenc e might have been due to a phenotypic response to the cold arctic clim ate. We discuss the lack of clear predictions regarding microtine adap tation to the unpredictable arctic environment, and emphasize that in terms of high reproductive rates in mammals, M. epiroticus represents an extreme case.