Multiple paternity in the bank vole (Clethrionomys glareolus):: field and experimental data

The frequency of multiple paternity was estimated in the natural populations of Clethrionomys glareolus in northeastern Poland, using enzyme electrophoresis. The percentage of multiply sired litters, those detected and undetected was 35.5 %. A laboratory experiment showed that 30 out of 44 bank vole females mated with two males during one copulatory series (consisting of mounts, intromissions, and ejaculations). Females showed clear preference to finish interrupted copulatory series with the second male, although the interruption of copulatory series did not reduce the chances of pregnancy under laboratory conditions. After the entire copulatory series, all females became non-receptive to any males. We found that under laboratory conditions the number of offspring fathered by the first male did not differ significantly from the number of offspring fathered by the second male. Thus, there are no differences in males' mating success with respect to the mating order in C. glareolus. Multiple paternity seems to be a result of social and spatial structure of bank vole populations. It probably evolved as a mechanism to prevent inbreeding.