9707220 Palumbi The genetic basis for variation in fertilization success will be determined by examining the interaction of eggs and sperm from a well-studied species of coastal marine invertebrate. Prior work on this species, the Hawaiian sea urchin Echinometra mathaei, has shown that different males possess different alleles for a gene that determines the attachment of sperm to eggs. The proposed research will determine whether males with different alleles have sperm with different attachment properties, and if eggs tend to be fertilized better by sperm from males with particular alleles. We will use a combination of microscopic eterminations of fertilization success of different males, and a PCR assay of which sperm actually fertilize which eggs to determine the degree to which genetic variation at the sperm attachment locus influences fertilization success. The interaction of eggs and sperm is crucial to successful fertilization, yet is one of the most difficult biological processes to study. The ability of different males to fertilize eggs from a particular female sometimes varies enormously, but we have little idea what types of mechanisms might cause this variation. Recently, it has been shown in some species that different males differ genetically at loci that determine aspects of sperm-egg attachment, and this provides a powerful system to investigate for the first time the genetic basis for differences in fertilization. The results will illuminate how natural selection might be acting to maintain fertilization polymorphisms in natural populations, and may help explain the rapid and novel patterns of molecular evolution at genetic loci involving gamete interactions.
