CYTOPLASMIC INCOMPATIBILITY IN DROSOPHILA-SIMULANS - DYNAMICS AND PARAMETER ESTIMATES FROM NATURAL-POPULATIONS

In Drosphila simulans, cytoplasmically transmitted Wolbachia microbes cause reduced egg hatch when infected males mate with uninfected femal es. A Wolbachia infection and an associated mtDNA variant have spread northward through California since 1986. PCR assays show that Wolbachi a infection is prevalent throughout the continental US and Central and South America, but some lines from Florida and Ecuador that are PCR-p ositive for Wolbachia do not cause incompatibility. We estimate from n atural populations infection frequencies and the transmission and inco mpatibility parameter values that affect the spread of the infection. On average, infected females from nature produce 3-4% uninfected ova. Infected females with relatively low fidelity of maternal transmission show partial incompatibility with very young infected laboratory male s. Nevertheless, crosses between infected flies in nature produce egg- hatch rates indistinguishable from those produced by crosses between u ninfected individuals. Incompatible crosses in nature produce hatch ra tes 30-70% as high as those from compatible crosses. Wild-caught infec ted and uninfected females are equally fecund in the laboratory. Incom patibility decreases with male age, and age-specific incompatibility l evels suggest that males mating in nature may often be 2 or 3 weeks ol d. Our parameter estimates accurately predict the frequency of Wolbach ia infection in California populations.