Male crayfish (Faxonius obscurus, Decapoda: Cambaridae) claws are longer and stronger yet comparable in shape during the reproductive season

Abstract

Abstract Animal weapons are diverse and often exaggerated structures associated with sexual selection and male–male combat. Despite their diversity, our knowledge of these structures comes primarily from studies that focus on the size of the weapons and neglect other components, such as their shape or performance. Furthermore, weapons can exhibit species-level plasticity based on nutrition and other ecological variables, but few studies have documented seasonal variation in weapon plasticity. Here, we investigate how weapon size, shape and performance differ across adult male reproductive and non-reproductive Allegheny crayfish, Faxonius obscurus. Given that F. obscurus and other cambarid crayfishes exhibit cyclical moulting between reproductive and non-reproductive states, they provide an ideal system in which to investigate such questions. We found that claws of reproductive and non-reproductive male F. obscurus differ in all three weapon components we investigated; claws from reproductive males were longer, stronger and different in shape compared with claws from non-reproductive males. Wielding longer and stronger claws is likely to confer greater competitive success during the mating season, which demonstrates an unexplored pattern of seasonal weapon plasticity. We discuss these results considering our knowledge of the seasonality of weapon phenotypes and propose several avenues of future research using cambarid crayfish as a model system.