Sexual dimorphism in performance and muscle allocation in the western painted crayfish Faxonius palmeri longimanus (Faxon, 1898) (Decapoda: Astacidea: Cambaridae)

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Multiple performance traits in animals can be affected by the same morphological feature. Armaments, or morphological weapons, and ornaments, morphological features used to attract mates, can have important influences on individual fitness. For example, ornaments of aquatic animals that improve fighting abilities or reproductive success can increase drag, resulting in decreased swimming performance. We investigated the effects of chela size on pinching force and escape performance in the western painted crayfish, Faxonius palmeri longimanus (Faxon, 1898). We predicted that individuals with larger chelae would swim more slowly than individuals with smaller chelae, and that males would be disproportionately affected because of male-biased sexual size dimorphism in chela size. We found support for our hypothesis that individuals with larger chelae would swim more slowly, but males and females were equally affected by large chela size, such that the differences in the scaling of chela growth did not correspond with differences in swimming performance for a given size. We also found that increased chela size in females corresponded strongly with increased strength. This was not necessarily the case for males, which exhibit three times as much variance in chela strength for a given chela size than females, potentially suggesting the use of dishonest signaling in this species. Muscle allocation differences between the sexes could also suggest that males can dishonestly signal their competitive abilities, such that weak males can have large chela. Our data support the idea of tradeoffs and lead us to further hypothesize about the roles of different life history strategies within the western painted crayfish.