Abstract
Lizards display a variety of social behaviour, such as aggregations, pair bonding, and group-living. Most knowledge surrounding lizard sociality comes from the well-studied Egernia genus of skink. However, little is known regarding what lizard sociality, social organisation and group living look like outside the Egernia genus. The Oligosoma genus of New Zealand skinks provides a unique perspective into understanding what social organisation looks like outside Egernia, and social evolution in lizards. Within Oligosoma our understanding of social behaviour is limited, but the Otago skink (Oligosoma otagense) has been observed living in pairs, groups, and aggregations of neonates. This study aimed to better understand the social organisation of the Otago skink, and what benefits may have allowed such social organisation to evolve.
Firstly, I investigated whether skinks live in defined communities that may constitute a social group and whether kinship and the age-class of individuals impacted this and overall social organisation. Secondly, I investigated whether skinks gain antipredator benefits from group-living. For this project, I studied a semi-captive Otago skink population at Orokonui Ecosanctuary, near Dunedin, New Zealand. To identify skink communities and the relative importance of kinship and age, I carried out behavioural observations, social network analysis and genotyping-by-sequencing. To assess whether Otago skinks gain antipredator benefits from group living, I conducted behavioural assays, vigilance recordings and observations of how often skinks were observed near cover relative to group size.
Skinks formed defined communities, possibly representing social groups. I did not detect a significant relationship between relatedness and social organisation at the network or community level. However, I was unable to genetically sample all individuals within the population, meaning it is possible a relationship was present, but remained undetected. Age class overall appeared to impact social organisation, as neonate and adult skinks overwhelmingly interacted with their age class (however this was not statistically tested in adults). In adults, I suggest such interaction patterns may be driven by 3 mate finding. Neonates interacted with each other significantly more than other age classes, and organised interactions with a significant degree of social preference.
Vigilance and behavioural assay results were not significantly different between grouped and solitary skinks. However, antipredator benefits may have been present, but not detected due to habituation and low sample size. Larger aggregations of skinks were observed near cover more than smaller groups and neonates were observed near cover more than adults, which both may indicate cover provides an antipredator benefit to skinks.
This study provides a unique insight into Otago skink social organisation and antipredator behaviour. Unique compared to other group-living lizards, I did not find evidence supporting social organisation based on relatedness, but rather relative ages of individuals. I did not find support for group-living providing antipredator benefits, which is a well observed function of group-living in some Egernia lizards. However, I did identify novel trends of larger skink aggregations being seen near cover more often, providing a basis for research into how habitat traits may influence skink aggregations. This study provides a snapshot of what lizard sociality looks like outside the Egernia genus, allowing us to draw greater comparisons and similarities of social organisation between phylogenetically different lizards.