9627879 BAUMANN Aphids and many other plant-feeding insects are dependent on specialized bacteria, called endosymbionts, that live within cells and that are transmitted from the mother insect to her offspring. The best documented function of endosymbionts within aphids is the provision of the essential nutrient, tryptophan. Because aphids do not ingest tryptophan in their diets, they depend on their endosymbionts to provide this nutrient. Thus the bacterial genes that underlie tryptophan production are critical to the growth and reproduction of the insect host. This study examines the evolution of the endosymbiont genes underlying tryptophan production in aphids. Previous work has indicated that these genes show an unusual pattern of accelerated evolution in the endosymbionts of certain aphid species. This project uses methods of molecular biology to test explanations for the variation in evolutionary rates in this gene. Because endosymbionts are an essential component of many crop pests, including such groups as aphids, whiteflies, and scale insects, this study will contribute to fundamental knowledge that could ultimately lead to progress in pest management. Agricultural entomologists have suggested that the short-term evolution of endosymbiont traits that affect insect performance is important in the origin of new strains of pest species. This study will be one of the first to directly examine evolution within endosymbiont genes that are critical to insect survival and reproduction.
