Maternal care in a social lizard: links between female aggression and offspring fitness

Infanticide is an important mortality factor for juveniles in a wide variety of taxa, and is thought to be an important influence on the evolution of pair bonding and parental care of offspring. Many parents, in response to conspecific infanticide, may alter their behavioural aggressiveness towards conspecifics in an adaptive manner to favour their offsprings' fitness. Research on conspecific aggression as an infanticidal counter-strategy by parents, however, has largely focused on mammals and birds. Owing to the almost ubiquitous occurrence of altricial young/parental provisioning of offspring in these taxa, our ability to test comparative hypotheses regarding the initial evolution of parental care is limited. Recent evidence of highly variable social systems within a monophyletic social lizard clade (Egernia spp.) provides an opportunity to further our knowledge in this regard. We examined patterns of aggressiveness towards a conspecific model by females from a wild population of social lizards (White's skink, Egernia whitii), while also documenting the first-year growth and survival of their offspring in the field. Female aggression increased during pregnancy and was maintained at a high level during postpartum periods, relative to aggressiveness during mating periods. We also observed consistent interindividual expression of aggressiveness in females, and offspring from more aggressive female behavioural phenotypes had higher rates of survival, but not growth, over their first year of life. These results suggest that relatively ‘simple’ forms of parental care (i.e. territoriality combined with kin tolerance) may favour offspring fitness and therefore parental care, without necessarily entailing the costs of full parental provisioning of offspring.