Parasites are ubiquitous and can exert powerful long-term selection on hosts. Host-parasite interactions may promote species diversity, alter host behavior, contribute to speciation and perhaps foster and maintain sex. My research uses a common arthropod parasite to investigate host-parasite coevolution. The parasite is a cytoplasmically transmitted bacterium that causes reproductive incompatability. Crosses between infected males and uninfected females are sterile. By "sterilizing" females not transmitting the parasite, infected males increase the frequency of infection and the parasite should spread until all individuals are infected. Two questions about host-parasite coevolution are addressed. Is there genetic variation for parasite-induced affects on host reproductive success? A genetic analysis measures the heritability of the parasite's effect on the host reproductive success. The response to selection (R) depends on selection (S) and heritability (h2), R=S*h2. Thus this experiment elucidates the potential of the host-parasite system to evolve. The second question is: How does parasite virulence evolve? Novel parasite strains will be introduced into different host genetic backgrounds. The parasite's effects on the host will be measured over long and short term. This experiment is an important test of models of parasite virulance. Together, these experiments provide important information on host-parasite coevolution.
