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BIOLOGICAL SCIENCES / EVOLUTION
Extraordinary intraspecific diversity in oyster sperm bindin
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*Scripps Institution of Oceanography, University of California at San Diego, La Jolla, CA 92093-0202; Department of Biology, University of Washington, Seattle, WA 98195-1800; Cawthron Institute, Private Bag 2, Nelson, New Zealand; and ¶Department of Genome Sciences, University of Washington, Seattle, WA 98195-7730
Communicated by Ryuzo Yanagimachi, University of Hawaii, Honolulu, HI, December 17, 2007 (received for review September 17, 2007)
In free-spawning invertebrates sperm–egg incompatibility is a barrier to mating between species, and divergence of gamete recognition proteins (GRPs) can result in reproductive isolation. Of interest are processes that create reproductive protein diversity within species, because intraspecific variants are potentially involved in mate choice and early speciation. Sperm acrosomes of the Pacific oyster Crassostrea gigas contain the protein bindin that bonds sperm to egg during fertilization. Oyster bindin is a single-copy gene encoding a diversity of protein variants. Oyster bindins have a conserved N-terminal region followed by one to five tandem fucose-binding lectin (F-lectin) domains. These repeats have diversified by positive selection at eight sites clustered on the F-lectin's fucose binding face. Additional bindin variants result from recombination in an intron in each F-lectin repeat. Males also express alternatively spliced bindin cDNAs with one to five repeats, but typically translate only one or two isoforms into protein. Thus, positive selection, alternative splicing, and recombination can create thousands of bindin variants within C. gigas. Models of sexual conflict predict high male diversity when females are diverse and sexual conflict is strong. The amount of intraspecific polymorphism in male GRPs may be a consequence of the relative efficiency of local (molecular recognition) and global (electrical, cortical, and physical) polyspermy blocks that operate during fertilization.
combinatorial diversity | F-type lectin | fertilization | polymorphism | sperm-egg binding
The authors declare no conflict of interest.
Data deposition: The sequences reported in this paper have been deposited in the GenBank database (accession nos. EF219425–EF219429).
This article contains supporting information online at www.pnas.org/cgi/content/full/0711862105/DC1.
To whom correspondence should be addressed. E-mail: stevan{at}u.washington.edu
© 2008 by The National Academy of Sciences of the USA
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