Meeting Abstract

8.1  Wednesday, Jan. 4  Oh snap! Sex, weaponry and aggression in snapping shrimp HUGHES, M.*; WILLIAMSON, T.; HOLLOWELL, K.; VICKERY, R.E.; College of Charleston, SC hughesm@cofc.edu

Sexual dimorphism in weaponry is often attributed to intrasexual selection, wherein one sex maximizes reproductive success through competition. In snapping shrimp (Alpheus spp.), sexual dimorphism in snapping claws – a deadly weapon – is common, with males having larger claws than females. If larger weaponry in male snapping shrimp results from selection on males for greater ability to compete for access to mates or resources necessary reproduction, we would predict that (1) males are more aggressive than females; (2) males exhibit more sex-specific aggression than females; and (3) species with more pronounced sexual dimorphism will exhibit greater aggressive behavior. To test these predictions, we staged competitive and pairing interactions in 2 species: A. heterochaelis and A. angulosus. Although they have proportionally smaller weapons, females of both species are more aggressive than males in competitive interactions, and in both species, females but not males exhibit sex-specific aggression. Finally, although sexual dimorphism is greater in A. angulosus, A. heterochaelis is more aggressive regardless of context. Female reproductive success is limited by body size; males, but not females, use claws as visual signals of size, suggesting that males may benefit from larger claws for functions other than their use as a weapon. Thus sexual dimorphisms in weaponry may result from differential advantages of investment in body vs. weapon size, rather than intrasexual selection for greater competitive ability in males.