The study of hybridization is important in evolutionary biology because it reveals the forces at work in the final stages of speciation. Some populations of animal species commonly hybridize, but it is usually difficult if not impossible to determine the causes hybridization in nature. The proposed research takes advantage of an exceptionally favorable situation for investigating the causes of hybridization and the reasons for relatively high fitness of the hybrids. On the small island of Daphne Major in the Galapagos archipelago the medium ground finch, Geospza fortis, occasionally interbreeds with two others; G. scandens, a resident species, and G. fuliginosa, an immigrant. Pedigree analysis has shown that hybrids may survive and breed as well or better than the parental species, over several years. Ecological reasons for their fitness will be investigated by intensive study of feeding efficiencies and diets. Possible advantages arising from enhanced heterozygosity will be assessed by an analysis of inbreeding effects in the G. fortis and G. scandens populations. Causes of interbreeding will be identified by statistical analysis of mating patterns. Results will be of theoretical importance to our understanding of speciation and the role of hybridization in maintaining genetic variation in small and potentially endangered populations.
