Variation in natural color influences mate choice in a fiddler crab (Leptuca leptodactyla)

In several species, natural variation in visible and ultraviolet (UV) light reflectance has been linked to individual reproductive quality. However, when evaluating the value of UV information, most studies employ experimental treatments that completely block UV light reflection, therefore disregarding individual variation in natural coloration. For instance, we already know that female fiddler crabs might refuse males whose claws are devoid of natural UV light reflectance (i.e., by covering them with sunscreen), yet it is still unclear how the natural variation in male fiddler crab claw coloration affects female mate choice. Here, we examine this question and hypothesize that female fiddler crabs can use natural male color variation as a parameter for partner selection. To investigate the preference of female fiddler crabs we set up an experimental arena in a mangrove area and presented female Leptuca leptodactyla (n = 100) with pairs (n = 100) of conspecific males. After registering a female's choice, we quantified the natural reflectance (i.e., color) from the enlarged claw of each male, by using a spectrometer, and extracted their colorimetric parameters (i.e., brightness, saturation and hue). Our results showed that females significantly favored males displaying higher brightness and lower green saturation. We discuss the possibility that brightness and saturation are redundant properties of the examined trait, both conveying information about male individual quality to females.