Parentage complexity in socially monogamous lemurs (Eulemur rubriventer): Integrating genetic and observational data

Genetic analyses of parentage sometimes reveal that "socially monogamous" (pair-living) species do not reside in strict family groups. Circumstances such as adult turnovers and extra-pair copulations, among others, may result in non-nuclear families. These genetic relationships within groups have implications for interpreting social behaviors. Red-bellied lemurs (Eulemur rubriventer) live in groups generally comprising an adult male-female pair plus immatures, and early genetic analyses of parentage in a relatively small sample suggested they mate monogamously. However, previous research on this taxon has also identified scenarios in which non-nuclear families might result, such as adult turnovers. To assess the potential occurrence of non-nuclear families in this "socially monogamous" taxon, as well as the social conditions under which they might occur, we combined behavioral observations of wild red-bellied lemurs in Ranomafana National Park with genetic parentage analysis of immatures from 17 groups. We found that the majority of groups (75%) represented nuclear family groups. However, 25% of groups represented non-nuclear families at some point during the study. The social factors that resulted in non-nuclear families were varied and included at least one adult turnover, and potentially delayed female dispersals and extra-pair copulations. Our results suggest that red-bellied lemurs are generally reproductively monogamous, with only limited evidence that non-nuclear families result from non-monogamous reproduction. However, similar to other pair-living primates, red-bellied lemurs appear to exhibit flexibility in their social organization and mating strategies. Multiple lines of evidence should be considered when inferring parent-offspring relationships within pair-living groups.