Mating System, Breeding Success, and Pup Mortality of a Habitat Specialist Rodent: A Field and Molecular-based Approach

Abstract

Mating systems are studied due to their interest in ecology and evolution. In rodents, mating strategies have been inferred from the spatio-temporal arrangement of males and females, and breeding success has usually been estimated through the number of embryos counted by palpation of pregnant females. However, these might not be trustable proxies to describe the mating systems and to estimate survival rate of pups. In this study, we surveyed breeding and reproduction of the southern water vole (SWV) (Arvicola sapidus) in six ponds over a three-year period. We combined capture-mark-recapture data with parentage analyses based on 444 individual genotypes with seven microsatellites: i) to estimate reproductive rate, ii) to compare field-based and molecular estimates of the mortality rate of juveniles and the effective breeding success of adults, iii) to find individual traits or environmental conditions related to breeding success, and iv) to describe the mating system of SWV. Our results suggest that mortality rate during the pre- and post-weaning period is around 63% and 27%, respectively, and reinforce our hypothesis that the high reproductive rates in SWV compensate for the high mortality of juveniles. Parentage analyses assigned one or two parents to 80% of the target juveniles and suggest promiscuity as the mating system of SWV, probably as a strategy to minimize infanticide by males, although deviations from promiscuity might arise depending on variations of ecological factors. Weight is positively correlated with reproduction rate, as heavier (dominant) females allocate nests in better habitat patches (minimizing nest predation) and heavier (dominant) males expand their home ranges so they can have access to more mates.