Interaction of drosophila and its endosymbiont wolbachia: natural heat shock and the overcoming of sexual incompatibility

SYNOPSIS. Wolbachia, a bacterial endosymbiont of diverse arthropods, affects its host's reproduction and so is consequential for its host's fitness. In the fruit fly Drosophila simulons, Wolbachia increases embryonic mortality in crosses of infected males with uninfected females, possibly by manipulating the proteins of the host gametes. Preliminary data suggests these proteins include at least two families of heat-shock proteins, Hsp70 and Hsp90. Drosophila larvae live within necrotic fruit, in which larvae can experience thermal stress that induces Hsp expression. Infected male D. simulons, if exposed to laboratory heat shock as larvae, father more viable offspring than unexposed controls. Also, infected male D. simulons, if allowed to 'copulate beforehand, father more viable offspring than virgin controls of identical age. These two mechanisms of restoring the reproductive compatibility of Wolbac/iur-infectcd Drosophila could affect the fitness of wild D. simulons; we are attempting to document these effects through modelling and experimental study of natural populations and their thermal environment. This research program exemplifies how evolutionary physiology may extend far beyond the classical disciplinary boundaries of physiology and evolutionary biology.