Higher relatedness within groups due to variable subadult dispersal in a rainforest skink, Gnypetoscincus queenslandiae

Field observations of groups of the prickly forest skink, Gnypetoscincus queenslandiae (Reptilia: Scincidae), from north-eastern Australia, that consist of different sized individuals under the same log have generated speculation about the social structure and dispersal patterns of this species. A total of 411 skinks were sampled from 12 rainforest sites on the Atherton Tableland in the Wet Tropics of north-eastern Australia. Relatedness statistics calculated using nine microsatellite DNA loci showed that prickly forest skinks are significantly more related to animals within their own group than to those in other groups, and there is a significantly greater relatedness between subadults less than 2 years old and adults within the same group. This relationship was no longer apparent between individuals estimated to be 2 to 3 years old and adults in the same group. Thirty per cent of individuals estimated to be less than 2 years old were likely to be the offspring of an adult under the same log, whereas only 7% of individuals between 2 and 3 years old were. Using mark-recapture techniques, movement distances between 0 and 94 m were recorded, with an average movement distance of 12.8 m, or 1.5 m per month between captures. Movements of 0-5 m were the most frequent for all ages and sexes. Subadults tended to move further per month on average than adults, but there was no difference in average movement between adult males and females. Thus I found little evidence to support a hypothesis of complex social structuring in prickly forest skinks. Rather, groups of lizards under logs appear to be a result of high, but variable, dispersal of subadults in their first 2 years.