Group structure and stability in social aggregations of white's skink, Egernia whitii

Most lizards display relatively simple social systems, but more complex and stable social aggregations appear to be common in one lineage of Australian skinks, the Egernia Group. Previous studies on this lineage have focused on species inhabiting crevices in large and disjunct rocky outcrops. Here, we describe the social organization of White's skink, Egernia whitii, a burrowing species that inhabits rocky habitats in southeastern Australia. We examined social group size, composition and stability over two field seasons using a capture-mark-recapture study, behavioral observations and genetic analyses. Twenty-four social groups, each comprising two to six individuals, were present at our study site, with 75% of lizards belonging to a social grouping. A higher proportion of adults than juveniles were part of a group, while more adult females belonged to a group than adult males. Groups generally comprised a single adult pair or an adult pair with juveniles. However, groups comprising one male with multiple females and multiple individuals of both sexes also were present. Groups were highly stable throughout the study, although individual group members were observed singly on half of all observations. Paternity analysis using four microsatellite loci revealed that juveniles within groups were closely related to adults in the group, with 38% living in groups with both parents and 71% in groups with at least one parent. Our data demonstrate the presence of complex sociality in a burrowing Egernia species and, together with previous studies, suggest that stable social organization is widespread across different habitats and phylogenetic groupings within the Egernia Group.