Repeatability and heritability of alloparental brood-care in a cooperatively breeding cichlid (#899)
For natural selection being able to act on a trait it has to be variable within the population, heritable, and affect individual fitness. Most research on cooperative behaviour has been dedicated to understand its adaptive function. In contrast, the genetic basis of cooperative behaviours and thus their potential to evolve as a result of natural selection has received much less attention. Here we present estimates of repeatability and heritability of cooperative behaviours in Neolamprologus pulcher, a cooperatively breeding cichlid fish. In this species subordinates carry out alloparental brood-care tasks, for instance cleaning a clutch and defending it against egg predators. N. pulcher subordinates differ both in the amount of helping and in the helping tasks they perform. First, we determined repeatability, i.e. the within-individual consistency of helping behaviours over time, as this parameter sets an upper limit to heritability. Second, we estimated heritability of helping behaviours, i.e. the proportion of the additive genetic variation of the phenotypic variation, to assess the potential of natural selection acting on these behaviours. We show that the estimates of repeatability of such cooperative behaviours are generally substantial but differ between behaviours: While egg care is highly repeatable, egg defence behaviours show intermediate repeatability. However, the heritability estimates for these behaviours are very low. To our knowledge, this is the first study to address the genetic basis of complex animal cooperative behaviour. Our analysis of variance components suggest that the high within-individual consistencies of helping behaviour over time are predominantly due to environmental effects while additive genetic variance has rather small effects. Since the number of helpers in N. pulcher groups varies greatly in the wild, we hypothesize that low heritability but strong environmental influence on the cooperative tendencies of offspring might facilitate the flexible adjustment of the amount of help needed in the territory.