Gene regulation as a modulator of social preference in voles.

Most mammalian species are nonmonogamous: the female alone cares for the young and males and females do not share nest sites. Within the genus Microtus, there exists ample diversity in social structure for neuroethological and neurobiological investigation. Prairie voles (Microtus ochrogaster) are socially monogamous: both the males and females contribute to care of the young within a shared nest site as a breeding pair through multiple breeding seasons. Closely related species such as the montane (M. montanus) and meadow (M. pennsylvanicus) voles do not typically show these behaviors. Over a decade of research has demonstrated that species differences in neuropeptide systems play significant roles in the behavioral divergence of these species. In particular, species differences in regional gene expression patterns of neuropeptide receptors in the brain mediate some of the behavioral traits associated with the divergence in social structure. Differences in gene expression patterns of a key gene in mediating social behavior, the arginine vasopressin 1a receptor (avpr1a), appear to be due to species divergence in a repeat locus in the 5' regulatory region of avpr1a. This highly repetitive locus is prone to expansion and contraction over relatively short evolutionary timescales and may give rise to the rapid evolution of sociobehavioral traits.