Although much research has been carried out on speciation in birds, we still know very little about the underlying genetic processes. In this project we explore two striking examples of ecological speciation in birds, namely the Nesospiza buntings in the Tristan da Cunha archipelago and the Crithagra (Serinus)/Neospiza finches on the Gulf of Guinea islands. In both systems, selection has been a major force during the speciation process and speciation could have occurred in the presence of gene flow (sympatric speciation in its broader sense). The study models are therefore expected to facilitate the detection of molecular signatures of adaptive divergence and speciation.
The Nesospiza buntings demonstrate adaptive differentiation of bill shapes and sizes, varying levels of pre-mating reproductive isolation between different bill morphs, and recent speciation. The Crithagra/Neospiza finches constitute an older radiation for which the link between different bill shape/size and resource use has not been established, because of the rarity or elusiveness of Neospiza concolor. However, available molecular data provides the best evidence for sympatric speciation that one could obtain in a natural avian system (Melo M, Stervander M & Hansson B, unpublished data).
We are now gathering genome-wide molecular evidence to test for alternative speciation hypotheses in the radiation of these two study systems, including the sympatric speciation hypothesis and a scenario based on hybridization following a secondary contact. Demonstrating sympatric speciation is nevertheless not a requirement for the research programme because there is ample evidence for a role of selection in these radiations, and the quantification of selection and its effect on the genome will be of importance regardless of speciation mode. We will search for genetic regions that are under selection, in order to determine the genetic bases of adaptation. In particular, we are interested in identifying genes underlying the evolution of bill size/shape. Bill constitutes a classic trait associated with resource-driven bird diversification, and therefore establishing the links between phenotypefitnessgenotype will significantly advance our overall understanding of speciation in birds.
Ryan P. G., Bloomer P., Moloney C. L., Grant T. G. & Delport W. 2007. Ecological Speciation in South Atlantic Island Finches. Science 315: 1420-1423.
Stervander M. 2010. Tracking genetic divergence in Gulf of Guinea finches strong support for sympatric speciation. MSc thesis in Molecular Ecology, Lund University.