The genetics of isolation: Genes for the origin of species

One of the fundamental goals of evolutionary biology is to understand the process by which new species evolve. Although dramatic progress has been made in understanding the importance of various geographical contexts and isolating mechanisms, the genetic basis of reproductive isolation, and therefore speciation, has progressed little. One reason for such slow progress is that genetic analysis of reproductive isolating mechanisms must be prefaced by the identification of isolating barriers important to speciation and by the development of genetic tools to address such traits. Oddly, progress along these two fronts has proceeded differently in different groups of organisms. Specifically, the genetic tools needed to address such complex questions have been developed in organisms for which the reproductive isolating mechanisms responsible for speciation have proven difficult to identify. Yet, those genetic model species are the species from which our current understanding of the genetics of speciation emerge.;In this dissertation, I take a distinctly different approach to studying the genetics of speciation by focusing on a system that is ideally suited to addressing reproductive isolation but lacks genetic tools. The ground crickets Allonemobius fasciatus and A. socius, perhaps due to their recent divergence (within the last 39,000 years), are reproductively isolated by a single barrier to gene flow. The nature of this barrier, conspecific sperm precedence, indicates that the genes involved with reproductive isolation are expressed within reproductive tissues. By focusing on messenger RNAs, the link between gene and protein, I use an expressed sequence tag approach to identify genes expressed within the male accessory glands, testis and the female sperm storage organ (or spermatheca) of these cricket species. Following a series of bioinformatic, gene expression and evolutionary analyses, I identify a number of candidate genes involved in conspecific sperm precedence, and thereby speciation.