Truly monogamous? Investigating multiple paternity in Eurasian beavers (Castor fiber) in a reestablished population in Austria

Knowledge on the mating system of a species is central to understand population dynamics and development. Special attention has been paid to the investigation of monogamous species and evolutionary causes and advantages of this mating system. However, social monogamy does not necessarily imply also genetic monogamy. Given the rarity of genetic monogamy in mammal species and the uncertain conclusions regarding multiple paternity in Eurasian beavers (Castor fiber), here, we undertake a further attempt to clarify the genetic monogamy of Eurasian beavers studying an Austrian beaver population by genotyping of gestating females and their foetuses at 19 microsatellite loci. Microsatellite analysis of mother–offspring groups suggest the occurrence of multiple paternity at a low level: two out of 42 litters (4.8%) were sired by two different males. We discuss the occurrence of extra-pair mating and potential drivers of multiple paternity in the light of beaver biology, population densities, territory characteristics and resulting activity ranges during reproduction period. Especially in the context of increasing beaver population densities in recovering populations and related increase of human-wildlife conflicts, sound knowledge on breeding biology, including species-specific reproduction tactics and their general applicability, is important for population monitoring.