Selection on two behavioral genes : fitness effects of receptor genes for arginine vasopressin 1a and oxytocin in the bank vole Myodes glareolus

Most variation in behavior is regulated by genes; nevertheless the mechanisms behind maintenance of genetic diversity at behavioral loci have remained mainly elusive in natural populations. I studied in my thesis selection mechanisms of two genes associated with socio-sexual behavior, arginine vasopressin receptor 1a (Avpr1) and oxytocin receptor (Oxtr) in bank vole (Myodes glareolus). Expression of Avpr1a and Oxtr in specific regions of the brain regulates diverse social and reproductive behaviors such as parental care, aggression, sexual behavior, social recognition as well as pair and parent- offspring bonding in mammals. In addition, there is a link between the length of a regulatory region associated microsatellite (RRAM) of Avpr1 and receptor density in the brain in some species. Bank voles have highly polymorphic RRAM in Avpr1a and Oxtr. My first study revealed that different length variants of RRAM allele in Avpr1 and Oxtr genes are maintained by balancing selection; more precisely the selection is sex-specific and dependent on population density. Different allele lengths were favored in males compared to females indicating that Avpr1a and Oxtr are sexually antagonistic (SA) genes. My second study showed that intrasexual competition in both males and females drives selection of Avpr1a RRAM lengths. My third study evidenced that bank voles bias their offspring sex ratio to mitigate sexual conflict caused by the SA Oxtr gene. My fourth study showed that individuals with the extreme lengths of Avpr1 and Oxtr RRAMs experience constraints in breeding success indicating stabilizing selection. In conclusion, my thesis provides evidence for diverse mechanisms acting on genetic diversity of behavioral genes.