Genetic and Reproductive Patterns within the Cactophilic Fly Species Drosophila pachea and their Association with Early Stages of Speciation

Abstract

Drosophila pachea is a cactophilic fly that feeds and breeds exclusively in necroting tissue of the senita cactus. Based on mitochondrial DNA loci, fly populations are genetically different between the two main regions (Baja and Sonora) of the fly's distribution. A single polymorphism Y linked fertility gene exhibit similar genetic patterns of regional differences within the species. Contrasting genetic patterns were observed based on microsatellite markers such that no regional split was identified. The species can be considered as a simple panmictic population along it's entire range. High remating frequency was observed in populations of both regions with equal number of offspring per father, suggesting that sperm competition might be limited within the fly populations. However, differential sperm use was observed between populations across the gulf of California. Sonoran male sperm produced more offspring than that of Baja males when females of both regions mated sequentially with males of these regions. The genetic pattern observed of higher variation within Sonora compared to Baja and a unique Y linked haplotype that is absent in Sonora and in relative high frequency within Baja suggest that unidirectional gene flow might occur within the species. These genetic patterns are in concordance with the reproductive behavior observations of higher Sonoran male productivity compared with Baja males.