Female choice in response to risk of sperm limitation by the stone crab, Hapalogaster dentata

Mating with males that have recently mated would be risky for females because the males may have limited sperm. Females should prefer males that can provide sufficient sperm for successful fertilization. We investigated whether female stone crabs prefer the larger of two males and which type of cue, visual or chemical, is more important for female mate preference. We then investigated whether females show mate choice in response to the risk of sperm limitation by exposing a receptive female in an aquarium to two males simultaneously: an unmated male with sufficient sperm reserves and a male with depleted sperm reserves. We tethered the males and wrapped their chelae to prevent interference in the females' choice. All females approached and mated with the larger males, indicating that females prefer larger to smaller males. Females located larger males by waterborne chemical cues. Using these cues, females showed a preference for unmated males with sufficient sperm reserves over sperm-depleted males, indicating that sperm limitation occurs in nature, and is a selection pressure in the mating strategy of female stone crabs. Thus, the influence of risk of sperm limitation on female choice should be considered in studies of sexual selection by field observations and laboratory experiments, and in sexual selection models.