Doctor of Philosophy

dissertationSperm competition is a pervasive mode of sexual selection across the phyla that have crucial implications in microevolutionary and macroevolutionary processes. Furthermore, females can bias the selection of sperm from one male over another in a process known as cryptic female choice. While sperm competition has been the subject of intense experimental research, very little is known about the molecular pathways and cellular mechanisms that regulate these processes. Insight into the molecular pathways regulating sperm competition and cryptic female choice are likely to have a high impact in the field of evolutionary biology since so little is currently known. The nematode C. elegans offers many advantages for the study of sperm competition. Male sperm exhibit a robust competitive advantage over hermaphrodite self sperm, resulting in the almost complete preferential use of male sperm. We have identified a gene, comp-1, that regulates several sperm behaviors leading to reduced male precedence when competing with both self sperm and other male sperm. Critically, mutant males and hermaphrodites have normal fertility, suggesting that mutants produce and transfer as many functional sperm competent for motility, sensation of guidance cues, and fertilization as do wild type. We have shown that the comp-1 sperm behavioral defects are specific to competitive contexts as comp-1 sperm are functionally normal when wild type iv sperm are absent. Surprisingly, wild type sperm appears to inhibit comp-1 sperm by altering the chemical environment of the hermaphrodite, most likely to involve prostaglandin signaling. Intercellular communication between the reproductive tract and sperm is fundamental for sperm migration, and prostaglandins have been previously identified as important for this process. However, this is the first time that prostaglandins have been implicated as necessary for sperm competition. Furthermore, prostaglandins are a novel mechanism of cryptic female choice and add to the field where very little is known about how females influence sperm competition. Results from our studies of comp-1 will provide insight into the molecular pathways necessary for sperm competition and cryptic female choice, which will ultimately broaden our knowledge of the mechanisms of evolutionary change