CAREER: Sperm Limitation, Sperm Competition, and Sexual Selection in Free Spawning Invertebrates

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Because sperm greatly outnumber eggs, evolutionary biologists have long thought that sperm competition is the selective mechanism driving the evolution of gender differences; males are limited by and compete for mating opportunities, while females are not limited by mates and exhibit mate choice. The evidence supporting these ideas come from species with internal fertilization or in situation where sperm are deposited on eggs. However, the ancestral, and still widespread, reproductive strategy is to release eggs and sperm into the environment where the chance of fertilization is much reduced compared to internal fertilization. Under these conditions, low densities of males and sperm can limit female reproductive success. This proposal will investigate how sperm and egg traits influence fertilization rates in the laboratory and ocean, how common sperm limitation and sperm competition are in natural invertebrate populations and how gamete competition can influence the evolution of gender differences in free spawning marine invertebrates. The work will involve laboratory and field experiments, at times using molecular techniques to better understand the evolution of mating systems.