Campbell 9806547 Hybrid zones are areas where related species, or other genetically distinct populations, come together and produce some viable offspring. Hybridization is particularly widespread in flowering plants and also occurs in many animal groups. Evolutionary biologists propose several models to explain patterns of genetic variation across the resulting hybrid zones. These models differ in the assumptions they make about natural selection on hybrids, and they have different important consequences for long-term evolution. Understanding the processes responsible for maintaining hybrid zones can also be applied to prevention of hybridization between crops and related weeds, and to conservation of rare species that occur near more common relatives. This study will test models for hybrid zones by comparing the lifetime fitness of parent and hybrid plants in the field. The investigators will follow the survival and final reproductive success of offspring generated from experimental crosses between two closely related species, Ipomopsis aggregata and Ipomopsis tenuituba, and planted as seeds into several locations. First generation and second generation hybrids will be planted. Each model can be distinguished by its unique predictions about the fitnesses of hybrids and parental individuals and how these change across environments. In addition, the investigators will determine whether interactions between pollen grains of the two species can reduce the level of hybrid formation and contribute to geographical variation in the extent of hybridization. This goal will be met using experiments and computer simulations to determine the mixtures of pollen that reach flowers in natural populations, and by performing experimental pollinations and genetic analysis of seeds.
