Adaptive radiation, the process by which species diversify to fill different ecological roles, is a central phenomenon in the evolution of biological diversity. Among bird families, the radiation of hummingbirds is exceptional in scope (over 320 species) and in the detail with which the adaptive significance of many anatomical features and behaviors have been studied. Our understanding of their radiation is hampered, however, because relationships among these birds are poorly understood; hummingbirds lack a fossil record and unrelated species may converge in anatomical traits characters because of similar nectarfeeding habits. Drs. Bleiweiss and Kirsch will examine the evolutionary relationships of hummingbirds by comparing directly their genetic material using the technique of DNA/DNA hybridization. With these data they will elucidate the interrelationships among many hummingbird genera, and determine which bird group is the family's closest relative. Using this information Drs. Bleiweiss and Kirsch will conduct several natural experiments that will test how DNA evolves. Hummingbirds are well-suited for such experiments because they represent the extreme among birds in several features presumed to affect rates of genetic change. The study will provide an important framework for understanding several basic evolutionary mechanisms associated with adaptive radiations. //
