Within-population variation in social strategies characterize the social and mating system of an Australian lizard, Egernia whitii

The lizard genus Eger nia has been suggested as an excellent model system for examining the evolution of sociality as it exhibits considerable diversity in social organization both between and within species. To date the majority of work examining the factors responsible for the evolution of sociality within Eger nia has advocated a broad scale approach; identifying the social structure of specific species or populations and comparing the degree of sociality between them. However, we argue that significant advancements could also be gained by examining variation in social strategies within populations. Here we integrate a detailed, 3-year, field-based examination of social spacing and juvenile dispersal with molecular analyses of paternity to determine the social and mating system of a Tasmanian population of White’s skink (Eger nia whitii). We show that E. whitii live in small stable family groups consisting of an adult male, his female par tner(s), as well as juvenile or sub-adults individuals. In addition, while the mating system is characterized by considerable genetic monogamy, extra-pair fer tilizations are relatively common, with 34% of litters containing offspring sired by males from outside the social group. We also show that traits related to social organization (social group composition, group size, stability and the level of extra-pair paternity) var y both between and within individuals. We suggest that ecological factors, such as habitat saturation, quality and availability, play a key role in maintaining between individual variation in social strategies, and that examining these individual level processes will allow us to more clearly understand variation in sociality among species.