Size, shape, and sex-dependent variation in force production by crayfish chelae

The ability to generate large closing forces is important for many animals. Several studies have demonstrated that bite or pinching force capacity is usually related to the linear dimensions of the closing apparatus. However, relatively few studies have applied geometric morphometrics to examine the effects of size-independent shape on force production, particularly in studies of crustacean pinching force. In this study, we utilized traditional and geometric morphometric techniques to compare the pinching force of Procambarus clarkii crayfish to their chela morphology. We found that males possessed larger chelae and pinched harder than females, but that their chela shape and size were weak predictors of strength. Female pinching force was significantly affected by both chela size and shape, with shape variation along the short axis of the claw contributing most to pinching force. We discuss our results in the context of reliable signaling of strength by males and females, and the different selective forces acting on chela shape in the two sexes.