EF 03: Evolutionary Ecology of Male-Killing Wolbachia in Drosophila Innubila

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Evolutionary ecology of male-killing Wolbachia in Drosophila innubilaJaenike, John R.University of RochesterWolbachia are intracellular, maternally transmitted, bacterial parasites present in the majority of insect species; their spread is accomplished by various means of manipulating host reproduction. Despite the potential ecological and evolutionary importance of Wolbachia, there has been very little research on Wolbachia dynamics and their effects on host insect populations in the field. This project focuses on the ecology of interactions between Drosophila innubila and the male-killing Wolbachia with which it is infected. Drosophila innubila inhabit mid- to high elevation forests in the sky islands of Arizona and New Mexico. Wolbachia cause almost 100% mortality of infected male embryos and infect a substantial fraction of females in these natural populations. This project will determine how the ecology of D. innubila allows the spread of male-killing Wolbachia. A series of field experiments will be carried out to assess whether infected flies suffer less competition than do uninfected flies. The project will also explore three mechanisms proposed to prevent fixation of male-killing Wolbachia within host populations: stochastic loss via incomplete maternal transmission, curing of the infection by antibiotic-containing mushrooms, and environmental temperature. Because D. innubila is distributed as isolated sky island populations, this species is ideal for investigating the effect of environmental gradients on Wolbachia dynamics. Finally, the project will quantify the effects of Wolbachia infections on the population-level sex ratio, mating frequencies, and sexual selection in D. innubila. It will specifically test predictions that the presence of male-killing Wolbachia at substantial infection frequencies results in a female-biased sex ratio in the population, lower rates of female mating, and selection on males to be discriminating in their choice of mates. The ecological focus of this proposal will contribute to understanding the dynamics of male-killing Wolbachia in natural populations and thus shed light on the feasibility of using these endosymbionts for deliberate manipulation of insect populations.