P3.119 Friday, Jan. 6 Population genetics of Heliocidaris sea urchins with benthic fertilization and brooded development HART, M.W.**; POPOVIC, I.; EMLET, R.B.; Simon Fraser Univ.; Simon Fraser Univ.; Univ. of Oregon firstname.lastname@example.org
Evolutionary changes in reproduction and development can affect rates of population divergence and speciation through both adaptive (e.g., sexual selection on gamete recognition proteins) and selectively neutral (e.g., genetic drift due to limited dispersal and gene flow) mechanisms of differentiation. We compared these two effects of life history differences among echinometrid sea urchins, and found that the evolution of benthic fertilization and development has a stronger effect on neutral population differentiation than on adaptive divergence of gamete recognition. Heliocidaris bajulus has benthic fertilization of large yolky eggs and brooded development of nonfeeding offspring tethered to the mother’s spines, and is closely related to the model organism H. erythrogramma. Compared to H. erythrogramma (with planktonic fertilization and dispersal of yolky lecithotrophic larvae), H. bajulus has strong population differentiation caused by low gene flow. This difference is consistent with the different modes of dispersal in the two species (and the loss of planktonic larval dispersal). In contrast, H. bajulus has slow rates of codon evolution of the sperm acrosomal protein-coding locus for bindin that are similar to rates in H. tuberculata and other echinometrids with small eggs and feeding larvae, and slower than previously reported fast bindin evolution in H. erythrogramma. This difference is not consistent with previous interpretations of fast bindin evolution in H. erythrogramma, which was provisionally ascribed to the evolution of large eggs that make large sperm targets at fertilization (with high risk of polyspermy), a trait shared in common with H. bajulus that evolved recently in their common ancestor. In this case fast bindin evolution may be linked to ecological differences that affect the risk of polyspermy rather than to differences in gamete traits.