Meeting Abstract

31.8  Tuesday, Jan. 5  Strongylocentrotus sea urchin eggs choose conspecific over heterospecific fertilization BIERMANN, C.H.*; WHITE, T.A.; PALUMBI, S.R.; Friday Harbor Labs and Portland State Univ.; Univ. of Washington, Seattle; Hopkins Marine Lab, Stanford biermann@pdx.edu

When given no choice, eggs of the green sea urchin Strongylocentrotus droebachiensis can be fertilized with sperm from the related, sympatric species S. pallidus and S. purpuratus. When green urchin sperm are added along with heterospecific sperm, conspecific sperm father over 90% of eggs – as assessed by genotyping three-day old embryos. The conspecific sperm precedence remains strong even if there is an excess of heterospecific sperm. However, if heterospecific sperm are given a head start, hybrid fertilizations increase. This increase is linear with delay time; conspecific fertilization reaches zero when heterospecific sperms had a one minute head start. In the reciprocal cross with eggs from S. pallidus, no-choice hybridization with S. droebachiensis sperm is lower with a mean of 40%, and conspecific sperm precedence is 100%. Strongylocentrotus purpuratus eggs block hybrid fertilization efficiently, even if given no choice. Strongylocentotus purpuratus sperm are very successful at fertilizing heterospecific eggs, and bypass the other species’ conspecific precedence to a small degree. These results suggest that hybrid fertilization studies should include sperm competition experiments since no-choice crosses are not representative even in simple broadcast-spawning systems.