Genetic and functional analyses of sperm length evolution in Drosophila

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Spermatozoa are the most diverse cell type, exhibiting rapid and dramatic evolutionary changes in form. However, the genetics and adaptive significance of sperm form are poorly understood. Investigations are proposed (1) to examine the relationship between sperm length and motility/behavior within the female reproductive tract, and (2) to identify genes of major influence on sperm length. These studies will be conducted with populations of the fruit fly Drosophila melanogaster that have been experimentally evolved to have unusually short or long sperm, and several closely related species differing substantially in sperm length. All populations have been genetically engineered to produce sperm whose heads glow green or red under fluorescent light. This material will enable, in the first investigation, unambiguous discrimination among sperm from different males within twice-mated females, as well as direct observation in vivo of real-time sperm motility and sperm-sperm and sperm-female interactions. The second investigation will use breakthrough gene sequencing technology (i.e., restriction-site associated DNA mapping) to identify genes associated with sperm length variation.The proposed research has the potential to generate watershed advances in the fields of reproductive physiology and genetics, sexual selection and speciation. Many undergraduate and graduate students will be trained in the course of this work. Resulting progress in our understanding of sperm behavior within females and the identification of candidate genes contributing to sperm form are also likely to lead to advances in our understanding and treatment of human infertility and in the further development of assisted reproductive technologies used in the preservation of threatened and endangered species.