Extrinsic and intrinsic constraints interact to drive extra-pair paternities in the Alpine marmot

To reproduce, animals have to form pairs and large variations in the degree of mate switching are observed. Extrinsic and intrinsic factors can constrain individual's mate switching. Among intrinsic factors, genes involved in pair-bonding, such as Avpr-1a, receive increasing attention. The length of microsatellites present in the regulatory region of Avpr-1a determines the neural densities and distributions of the vasopressin receptors known to impact pair-bonding behaviours. For the first time, we investigated whether and how the genetic makeup at Avpr-1a, an intrinsic factor, and the social context, an extrinsic factor, experienced by wild Alpine marmot (Marmota marmota) females affect the proportion of extra-pair young. This proportion was positively correlated with the length of their Avpr-1a regulatory region but only when the social constraints were relaxed, that is when mature male subordinates were present. When ignoring the interactive effect between the length of their Avpr-1a regulatory region and the social constraints, the genetic makeup at Avpr-1a was not associated with the proportion of extra-pair young. Under natural conditions, the genetic regulation of pair-bonding could be hidden by extrinsic factors constraining mate choice.