Meeting Abstract

85.5  Tuesday, Jan. 6  Do Horseshoe Crabs Benefit from Polyandry? JOHNSON, S.L.*; BROCKMANN, H.J.; University of Florida; University of Florida sheriljohnson@ufl.edu

Why females mate with several males when the sperm from a single male is often sufficient to fertilize all their eggs is one of the most perplexing questions in evolutionary biology. Direct benefits (e.g., nuptial gifts, paternal care) to multiple mating are not expected in externally fertilizing species. Females may gain from mating multiply by insuring fertilization, increasing offspring diversity, improving male quality (good genes) or increasing genetic compatibility. Alternatively, multiple mating may result in a net cost to females as a by-product of male-male competition (convenience polyandry). We compare the reproductive success of monandrous and polyandrous females and evaluate the importance of good genes and genetic compatibility in a natural population of the American horseshoe crab, Limulus polyphemus. In this species attached pairs migrate to shore and spawn on high tides; the male fertilizes the females eggs externally with free-swimming sperm as the eggs are being laid in the sand. Unattached males are attracted to spawning pairs by visual and chemical cues and become satellites of some (polyandrous) females while ignoring others (monandrous). When present, satellites fertilize a high proportion of the females eggs. We observe monandrous and polyandrous females and compare reproductive measures such as the rate of egg laying, the number of eggs layed, and developmental rates of offspring. We evaluate the importance of good genes and genetic compatibility by conducting in vitro fertilization experiments. As an ancient and independently evolved arthropod, and the only arthropod with external fertilization, Limulus provides a unique opportunity to extend our understanding of the evolution of multiple mating.