9726272 Hodges Two species of the columbine genus Aquilegia, A. formosa and A. pubescens, have very different floral morphologies and are predominantly pollinated by different animals. A. formosa has red, pendent, short-spurred flowers pollinated by hummingbirds and A. pubescens has white, upright, long-spurred flowers pollinated by hawkmoths. While these two species are fully compatible in controlled crosses, they rarely crossbreed in nature due to the differences in their flowers. The two species' distributions overlap in the southern Sierra Nevada mountains of California where narrow hybrid zones form. We will determine the number of genes responsible for the differences in floral morphology by utilizing techniques developed for animal and plant breeding. Because hybrid zones do occur where these species overlap, genes from one species that are not affected by natural selection can penetrate beyond the hybrid zone into the other species. However, genes that are affected by natural selection are prevented from penetrating the alternate species. We will determine how natural selection acts on each segment of the genome by measuring the degree it is able to penetrate beyond the hybrid zone. A major goal of evolutionary biology is to understand the genetic basis of traits conferring reproductive isolation. These traits are responsible for the generation and maintenance of biological diversity. Many scientists believe that most adaptive differences between species arise from the accumulation of many small genetic changes while others believe that they arise from a few changes with large effects. This issue has remained unresolved because detailed genetic studies have been limited to only a few model organisms. In addition, the number of traits and the proportion of the genome important for species isolation is unknown. By synthesizing genome mapping techniques with hybrid zone analyses a detailed examination of the genetics of specie s isolation will be possible.
