Claw coloration in the fiddler crab Leptuca uruguayensis has no correlation with male quality

Abstract

Sexual selection is thought to play a major role in the evolution of color due to the correlation between a signaler’s physiological state and the displayed color. As such, researchers often investigate how color correlates to the quality of the signaler, like size or body condition. However, research on the relationship between color and individual quality is often taxonomically limited and researchers typically investigate how color phenotypes relate to one index of quality, such as a linear measure of body size. Here, we investigated the relationship between body size, claw size, claw muscle mass, lipid content, and the color of the claw in male fiddler crabs (Leptuca uruguayensis) which wield an exaggerated claw that varies in color from brown to red. We hypothesized that if color was correlated to one or more indices of male quality, the color displayed on the claws of male L. uruguayensis could be under sexual selection. We found Leptuca uruguayensis claw color varies substantially among the individuals we photographed. However, we did not find a correlation between claw color and indices of quality; neither brightness nor hue correlated to the indices of quality we measured. Our findings suggest that claw color in L. uruguayensis is unlikely to have evolved to signal quality, but may instead function as a species identity or as a non-indicator sexual signal.