Collaborative Research: Postmating Reproductive Isolation Among Drosophila arizonae and Drosophila mojavensis

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0075312 MarkowThe crucial event for the origin of new species is the formation of reproductive isolation. How one species splits into two reproductively isolated groups of organisms, however, is poorly understood. Fruitflies of the genus Drosophila have been a model system for studies of speciation. These studies have focused on premating or postzygotic isolating mechanisms, or those processes that determine whether or not males and females mate and whether or not they produce viable and fertile offspring, respectively. The multitude of events occurring between insemination and egg fertilization has been largely ignored in studies of speciation. Recent work, however, indicates that sperm, seminal fluid, and female reproductive tract characteristics that are of central importance for successful reproduction are rapidly divergent. The investigators postulate that this divergence will cause diminished reproductive success whenever members of genetically differentiated populations interbreed, and they propose a series of experiments to explicitly test this hypothesis using D. arizonae and its sibling species D. mojavensis, both endemic to North America. Because D. mojavensis from different geographic regions are considered to be incipient species, the investigators will take advantage of a naturally occurring continuum of reproductive isolation for testing their predictions. Preliminary data indicate that populations of D. mojavensis differ significantly in the traits to be measured. By conducting laboratory crosses between members of different populations and species with known reproductive characteristics, the investigators will determine how these characteristics lead to reproductive barriers central to the formation of new species. Results of these experiments may have important implications for the formation of new species.