The Genetics of Reproductive Isolation: Co-Evolution, Polymorphism and Functional Differentiation of Gamete Recognition Loci in Sea Urchins

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9510407 PALUMBI Understanding how species originate has been one of the most important, yet one of the most difficult, challenges in biology. One of the largest gaps in our understanding of the origin of species concerns the genetic changes that accompany reproductive isolation. This proposal describes new experiments in one such emerging model system: hyper-variable gamete attachment genes in recently diverged sea urchins in the genus Echinometra. These species are reproductively isolated by the failure of sperm to fuse with eggs of different species. Our prior work has shown that the sperm attachment protein bindin has diverged greatly between Echinometra species, and is extensively variable within species. Because of active work on the molecular biology of sea urchin fertilization, we can now also examine the gene for the egg receptor, and for the first time study the co-evolution of interacting genes involved in reproductive isolation. We will examine bindin/receptor co-evolution by sequencing the egg receptor gene in Enhinometra and comparing results to our existing bindin sequences. cDNA sequences of the 4 Indo-Pacific Echinometra species will be used to test for patterns observed in bindin. The results will allow us to understand the co-evolution of proteins that are closely involved in the mechanisms that define species boundaries. Our studies are also important for basic research on mechanisms of fertilization, and how egg and sperm successfully recognize one another.