Vasotocin influences mother-offspring associations in a facultatively family-living lizard.

Parent-offspring associations provide the basis for more complex care and breeding systems. One proximate mechanism by which parental behavior is facilitated across animal taxa is via nonapeptide hormones such as arginine vasotocin (AVT). However, existing research largely comes from obligately social species, and whether such mechanisms are conserved in social systems where care is facultative remains unclear. Here, we used a facultatively family living skink, Liopholis whitii, to test the role of AVT in mediating 2 key parental behaviors: parent-offspring associations (measured by proximity between mothers and offspring) and maternal aggression (in response to a conspecific model). We found that increasing AVT via intraperitoneal injection led to more time spent in closer proximity between mother and offspring. Conversely, a decrease in AVT signaling (using an AVT receptor antagonist) resulted in a reduction in the time spent in closer proximity. We also found that these effects caused by increased AVT signaling persisted for several weeks, suggesting a potential organizational effect of AVT on the mother-offspring relationship. Contrary to our predictions, we found no effect of AVT manipulations on maternal aggression, suggesting that AVT may have been de-coupled from its usual role as a moderator of aggression. These results support the idea that AVT may be a mechanism involved in governing parental behavior in this system, and as such, could have played a key role in the repeated evolution of group living.