Two fundamental predictions from the field of population genetics have yet to be satisfactorily tested in natural animal populations. The first prediction is that philopatry (the tendency, common to social species, for individuals to settle and breed close to their place of birth) leads to increased genetic similarity of individuals in local areas and greater genetic differences between individuals from different localities. The second prediction is that high variance in reproductive success (another tendency common to many social species, whereby some individuals produce more than their share of offspring while many others produce none) also increases the genetic similarity of individuals within a local population. Cooperative breeding is a type of sociality seen in some birds and mammals; cooperative breeders are characterized by both greater philopatry and high variance in reproductive success relative to non-cooperative species. This study uses two Australian bird species, the cooperatively breeding Brown Treecreeper (Climacteris picumnus) and the non-cooperative White-throated Treecreeper (Cormobates leucophaea), to test the predictions stated above. The investigators will collect data on current levels of philopatry and variance in reproductive success in the two species, while simultaneously analyzing genetic data at varying spatial scales, ranging from local to landscape levels. Unlike previous studies, this study takes advantage of recent improvements in lightweight radio transmitters to monitor individual movements, as well as recently developed genetic markers (microsatellite DNA) for assessing genetic similarities and differences between individuals.
The predictions detailed above form two of the cornerstones of population genetics, yet this study will be the first to critically evaluate them outside of the laboratory. Doing so will improve understanding of how the ecology, behavior, and genetics of a species interact at the population level to produce such an astonishing variety of social systems. Specifically, these data will be used to test alternative theories regarding the evolution of altruistic behavior in general, and of cooperative breeding in particular. The research will illuminate why one species becomes highly social, exhibiting many cooperative behaviors, while another closely related species remains relatively asocial, exhibiting predominately selfish behaviors. Further, this study will promote a better understanding of how levels of sociality and cooperation in a species might affect the potential for further evolutionary change.
