Genetic relationships within colonies suggest genetic monogamy in the Eurasian beaver (Castor fiber)

Social monogamy, considered rare in mammals, has been described in two species of beaver, the Eurasion beaver (Castor fiber), and the North American beaver (Castor Canadensis). Social monogamy, however, does not necessarily imply genetic monogamy. For example, in group living mammals, females may engage in extra-pair copulations as a result of increased female mate choice opportunities. Recently, following genetic analysis, a wide range of genetic relationships among colony members have been documented in the North American beaver, including extra-pair paternity. Here, we used microsatellite loci to provide parentage estimates from colonies of the Eurasian beaver in the Kirov region, Russia. No evidence for the presence of any extra-pair young was detected. However, in two cases, we found a pair of unrelated males inhabiting a single colony. Our results suggest that while colonies may comprise both related and unrelated individuals, the genetic mating system appears to match that of the previously inferred social monogamy.