Nuptial coloration in fiddler crabs as an indicator of reproductive quality

Abstract Individual quality can be signaled through ornaments or body coloration that correlate with nutritional status, physical strength, body size, and reproductive potential. These signals can be dynamic, varying throughout the individual's lifetime or adjusting rapidly to environmental changes. In fiddler crabs, body coloration changes throughout their life cycle, including shifts in color, pattern modifications, or rapid darkening or whitening of the carapace, and is associated with the species’ reproductive peak. However, the role of carapace whitening as a signal of individual quality remains unclear. This study investigated whether white-carapace males of Leptuca leptodactyla exhibit superior quality or reproductive traits compared with dark-carapace males, and whether this white coloration is perceived by females. To address this, we compared the coloration of males with white and dark carapaces, as well as their physical strength, claw mass, claw size, and gonadal maturation stage. Our results indicate that males with white coloration have heavier claws, a higher proportion of developed gonads, greater body brightness, and are preferred by females. Thus, we demonstrate that white carapace coloration in L. leptodactyla signals better development and reproductive maturity, potentially influencing female mate choice.