9321243 Hellberg Closely related species of marine invertebrates commonly occur together and often spawn simultaneously, yet hybrids between these species rarely form. Proteins on the surface of the gametes control species-specific fertilization. Three lines of evidence suggest that changes in these gamete recognition proteins may be involved in the evolution of reproductive isolation: 1) non-fertile heterospecific crosses usually result from the failure of sperm to attach to heterospecific eggs, 2) closely related, reproductively isolated species often show little overall genetic divergence, and 3) selection promotes the divergence of sperm-borne gamete recognition proteins found in different species of abalone. This project will examine two critical questions which remain unanswered: 1) Are interspecific differences in gamete recognition proteins greatest in geographical areas of species overlap, and 2) How variable are gamete recognition proteins within species? These two questions will be addresses by documenting nucleotide sequence variation of the sperm borne gamete recognition protein bindin from both co-occurring and isolated populations of Pacific sand dollars. The project will focus on members of the genus Dendraster, whose geographical distribution (both overlapping and non- overlapping regions) and very recent origins (1 May) should facilitate discrimination between alternative evolutionary mechanisms driving bindin divergence. Finally, the functional significance of both inter-and intraspecific variation in bindin will be examined using pairwise fertilization assays. This research project should produce novel insights into the role of the potential for interspecific hybridization in promoting the divergence of gamete recognition proteins. ***
