LAUSR

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.