Ecology and population genetics of Sonoran Desert Drosophila

Three species of cactophilic Drosophila endemic to the Sonoran Desert of No rth America, D. nigrospiracula, D. pachea and D. mettleri, experience marke d differences in spatial resource availability, and the first two of these display significant differences in dispersal behaviour. We employed starch gel and cellulose acetate electrophoresis for eight allozyme loci to test f or a relationship between these variables and genetic differentiation among geographical populations of each species. No evidence was found for popula tion structure in any of the three species, populations of which were separ ated by geographical distances of up to 475 km. Allele frequencies for two loci, Mdh-1 and Est-2, in D. nigrospiracula and D. pachea were very similar to those obtained approximate to 30 years ago by other workers, indicating that the polymorphisms are remarkably stable under the stressful and varia ble conditions of the desert environment. High longevity, dispersal and mul tiple female remating are likely to contribute to the apparent high level o f gene flow in all three species.