Density-dependent changes of mating system and family structure in Brandt's voles (Lasiopodomys brandtii)

A mating system is an important life history for animals dealing with
changing environments. Population density affects the plasticity of a
mating system and subsequently the family structure of animals, but its
impacts on mating systems and social structures are rarely investigated by
using molecular markers in field conditions. In this study, using
microsatellite genetic markers, we examined the changes in the social and
genetic mating system and family structure of Brandt’s voles in the
grassland of Inner Mongolia, China, under low-, medium-, and high-density
enclosures (each enclosure 0.48-ha with 4 replicates.) We found, that with
the increase in population density of the founder voles introduced into
the enclosure in early spring, both sexes increased their number of
genetic mating partners, while males increased their social partners,
resulting in a more promiscuous mating system. The number of genetic
fathers and mothers per family, the number of social offspring per founder
male or female, and the proportion of extra-group offspring increased with
increased density, indicating that the response of the family structure to
density change which is consistent with the change in mating system
observed in our study. Both male and female voles had multiple mates, but
males had a larger number of social and genetic mates, the number of
social and genetic offspring, and the number of social and genetic
families. Our study highlights the significance of density-dependent
plasticity of a mating system and family structure in affecting the
population change of small mammals.