Vole species as an animal model for the evolution of social behavior: from genes to brain to behavior

The vole genus Microtus shows extraordinary diversity in the range of social behaviors among closely related species. A few species，such as Microtus ochrogaster and pinetorum (prairie and pine vole), show monogamous social organization, while other species such as Microtus montanus and pennsylvanicus (montane and meadow vole) are solitary and promiscuous. Monogamous prairie and pine voles display selective and long-lasting pair bond formation between adult mates and biparental care of the offspring both in nature as well as in the laboratory. The neuropeptide vasopressin is involved in the neural regulation of monogamous behavior in vole species. Here, we review the past and current findings related to the vasopressin system and pair bond formation in voles. First, we review vole species differences in the distribution of vasopressin VI a receptors (ViaR) in the brain as a means to identify the role of specific brain regions in pair bond for mation. Next, we discuss pharmacological manipulations with VIaR antagonist administered into specific brain regions to determine which regions are necessary for pair bond formation. We also describe vole species differences in V1aR gene structure and function and potential contribution to species differences in VIaR brain distribution and behavior. Lastly, we discuss novel findings in which gene manipulation of brain VIaR in a promiscuous vole species confers monogamous behavior. Thoroughly understanding the genetic and neural mechanisms underlying a complex social behavior can have significant implications for understanding the evolution of diverse behavior between and within pecies.