Meeting Abstract

31.6  Tuesday, Jan. 5  Reproductive character displacement in egg-jelly carbohydrates reinforces mating barriers in two broadcast-spawning marine invertebrates MARKS, J.A.**; BIERMANN, C.H.; Univ. of Oslo, Norway; Portland State Univ. Jessica.Marks@bio.uib.no

In marine broadcast-spawning organisms, geographic divergence in gamete compatibility may reflect the first step toward speciation, yet little is known about patterns of pre-zygotic isolation among populations or mechanisms involved in the formation of reproductive barriers. We determined fertilization success within and between Strongylocentrotus droebachiensis and S. pallidus, two closely related species of sea urchins that overlap in geographic distribution and spawning season. We studied populations of both species from the NE Atlantic (Norway, Svalbard) and the NE Pacific (WA). In sea urchins, carbohydrates in the egg-jelly coat trigger the sperm acrosome reaction, a necessary step in the fertilization cascade that is a species-specific mediator of fertilization in these species. Eggs can also discriminate among sperm using the sperm protein bindin and its egg receptor. To elucidate the mechanism behind gametic incompatibility, sperm were also pre-treated with egg jelly. We found greater incompatibility in heterospecific crosses in sympatry than in allopatry, a pattern of reproductive character displacement that is consistent with reinforcement. Pre-treatment with egg jelly mitigated this effect, implicating divergence in egg-jelly carbohydrates but not sperm bindin. In contrast, intra-specific barriers among allopatric populations reflect divergence in bindin; for most populations, conspecific crosses had lower fertilization in allopatry that could not be remedied by pre-treatment with egg jelly. We demonstrate reproductive character displacement in a broadcast-spawning marine invertebrate and suggest barriers to fertilization can arise through different mechanisms operating between individuals, populations and species.