Social behavior refers to any interactions between two or more conspecifics. A relatively common social behavior in the animal kingdom is group living, which provides benefits to group members (e.g., enhanced vigilance and predation avoidance). Predation risk is an important force that selects for behavioral traits, and promotes the evolution of sociality favored by kin selection. Most studies of sociality have focused on animal groups in which interactions are overtly obvious. Although interactions differ among the various vertebrate lineages, taxa are often categorized as social or non-social, ignoring the diversity and complexity of social behavior. Reptiles have been usually labeled as non-social; however, the degree of sociality can vary among species as shown in the genus Egernia. Liolaemus leopardinus is a high-elevation lizard species endemic to the Chilean Andes. It is viviparous, lives in large colonies, and adults and juveniles are highly social, but little is known about the natural history of the species. Our findings over two field seasons suggest that bird predation causes mothers of L. leopardinus to engage in parental behavior, and that predation by birds forces newborns of the species to behave secretively and to seek solitary refuge underneath rocks partially covered by bushes. Skeletochronology revealed the formation of annual growth rings in the phalangeal bones of subjects of L. leopardinus; however, the method was poorly suited for aging individuals. However, when body size of various free-ranging subjects repeatedly captured and measured was plotted against activity periods of three years, we could assign individuals to four age groups, and estimated the age when female lizards became sexually mature. We provide spatial, behavioral, and genetic evidence that supports the conclusion that L. leopardinus forms social groups of closely related individuals with non-relatives mixed in. Genetically related juveniles and adults spend time in close association, share home ranges and communal refuges during the day and night, and overwinter together in deep rock crevices. As a whole, our study revealed fine details regarding the gregarious behavior of L. leopardinus, a social but highly secretive species. We suggest that predation, kin recognition, and roosting drive the evolution of sociality in L. leopardinus, and not thermoregulation, refuge availability, or food.Zoolog
