Female northern myotis (Myotis septentrionalis) that roost together are related

Selection for cooperation, including nepotism, acts on individuals and so quantifying the genetic relationships between individuals that interact often is fundamental to understanding the evolution of sociality. Compared with stable kin groups, relatively little is known about the genetic relationships within groups with fission–fusion dynamics, and in particular between pairs that form long-term relationships. We examined the genetic relationships among female northern myotis, Myotis septentrionalis, that roost in maternity colonies consisting of multiple social groups, within which pairs form long-term relationships (i.e., familiar pairs). Using microsatellites and mitochondrial DNA, we found that females within colonies were not more closely related to one another than they were to females in neighboring colonies at the nuclear level, but they were at the maternal level. Females within social groups were more closely related than expected by chance at the nuclear but not at the maternal level. Furthermore, a comparison of pairwise associations and pairwise relatedness revealed that familiar pairs were more closely related than expected by chance at both the nuclear and maternal level. Kin selection may, therefore, play a role in shaping relationships within groups with fission–fusion dynamics.