Evolutionary genetics of social behaviour in birds

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The existence of cooperative behaviour has posed a major problem for evolutionary biologists since Darwin first recognised that natural selection predicts selfishness rather than cooperation. Therefore, the sophisticated societies of social insects (ants, bees and wasps) and the cooperative breeding systems of many vertebrates, where non-breeding helpers assist breeders in raising their offspring, have been a major focus of research by evolutionary biologists. The biggest advance since Darwin in our understanding of such behaviour was the introduction of the concept of kin selection (inclusive fitness theory) by Hamilton in 1964. The key insight was the idea that individuals could increase their evolutionary fitness by increasing the survival or productivity of their relatives, as well as through personal reproduction. However, the role of kin selection in the evolution of the cooperative breeding systems of vertebrates remains a matter of considerable debate. One of the problems underlying this gap in understanding is the difficulty of measuring the fitness gained directly via personal reproduction, and that gained indirectly through kin-selected cooperation. The first objective of this project is to partition fitness in this way in the cooperative breeding system of the long-tailed tit Aegithalos caudatus. Long-tailed tits are unique among UK birds in having a cooperative breeding system in which birds who have failed in their own breeding attempt seek out the nest of a relative in the same population and become helpers by assisting them in raising their offspring, thereby gaining indirect fitness benefits. The long-tailed tit provides an excellent model system for this project because they have been the subject of a long-term (since 1994) field study in which many relevant behavioural and life history traits have been measured in a systematic fashion each year for a large number of individuals (>2500 birds to 2010). This has allowed us to measure the reproductive success (i.e. fitness) of a large number of individuals. We have also established a social and genetic pedigree that will allow us to use quantitative genetics to determine the genetic and environmental basis for variation in key behavioural and life history characteristics associated with the evolution of social behaviour in this species.More specifically, using the network of relatives in our pedigree we will investigate whether measures of fitness and cooperative behaviour are heritable traits. Secondly, we will investigate whether particular features of individuals' behaviour, morphology and/or life history vary with either their direct or indirect fitness. We are particularly interested in the likely sex differences in cooperative behaviour, hence sex differences in the kind of fitness individuals gain, and the consequences of this for the evolution of other traits linked to direct or indirect fitness in males and females. Finally, we will use this study system to address another long-standing question in evolutionary biology: if particular traits (such as cooperative behaviour) are heritable and linked to fitness, how is variation in those traits maintained? We will examine whether spatial and temporal variation in the environment influences the relationship between fitness and specific traits.