Abstract
The study of sociality in a conservation context is a growing area of science often applied across a variety of taxa, from primates to social insects. However, the study of social systems in in lizards has been limited to just a few species. This study examines the social networks and nature of social interactions in two sympatric lizard species, the Otago skink (Oligosoma otagense) and the grand skink (O. grande). These two species share a similar biology and are observed cohabiting the same rock tors. However, sociality has not been studied in grand skinks while Otago skinks have been found to form stable social networks in a captive population.
Photographic surveys were conducted over a three-month period at five sites within a wild metapopulation of grand skinks and Otago skinks. These five sites varied in the relative proportion of Otago skinks and grand skinks, from Otago skink dominated sites to grand skink dominated sites. Skink-skink behavioural interactions and basking proximity were recorded and photographs were used to identify the skinks involved in these observations. Pairs of skinks were considered to be interacting peacefully if they were basking within one metre of one another, with interactions categorised into four proximity thresholds: 1m, 30cm, 10cm and touching. An interaction was deemed agonistic if it involved an aggressive behaviour or submissive reaction. Network analysis was conducted to compare the number of interactions between juvenile and adult skinks as well as between Otago and grand skinks. The nature and probability of interactions between and within these groups were also compared. In addition, the presence of tail damage was examined as a potential indicator of the probability of aggressive interactions occurring.
This study found that the social networks and aggregative basking previously observed in a captive population of Otago skinks also occurs in this wild population. The number of Otago skinks interacting decreased as the ratio of grand skinks to Otago skinks increased. In contrast, grand skinks were not seen as seen basking in aggregations and participated in agonistic interactions more often than Otago skinks. Interspecific interactions were rare, consisting of a combination of peaceful and aggressive interactions. The presence of tail damage did not appear to be related to the probability of an individual interacting or involvement in aggressive interactions. However, tail damage was more common at sites that were nearest to a nest of starlings.
It appears both skink species interact less often with conspecifics when the tor is inhabited by a larger number of the other species. Further study is needed in order to understand whether these social interaction rates are associated with population survival and growth. Due to the nature of the Otago skink social structures, it may be beneficial to take existing connected networks into consideration when selecting skinks for translocation. Although, the effects of breaking these networks, such as family groups, on juvenile survival and adult interactions need further research. A multi-year study would increase understanding of the nature of Grand skink agonistic interactions and the stability of pair bonds.