Thin-fingered fiddler crabs display a natural preference for UV light cues but show no sensory bias to other hypertrophied claw coloration

Abstract

Although color cues play an important role in sociosexual signaling, when communication is exploited as a foraging cue by predators, prey must pay the due cost for sustaining information interchange. In this regard, fiddler crabs draw attention by having flashy enlarged claws that could potentially attract the interest of many predators. Surprisingly, the adaptive function of claw coloration in fiddler crabs is not entirely understood and have barely been studied in American species. Here, we examine the spectral reflectance of thin-fingered (Leptuca leptodactyla) fiddler crabs’ hypertrophied claws and evaluate whether female conspecifics prefer UV-light or other color cues. We test whether male claws reflect UV light and whether females use UV light and/or other color cues when making mating decisions. Our results reveal that only the most flamboyant enlarged claws should be detected by female conspecifics, which show a clear preference for male UV signals. Moreover, while the anterior portion of the enlarged claws (pointing towards conspecifics) reflect UV light, claws’ dorsal portion and carapaces (which possibly point upwards and might attract airborne predators) do not show an UV peak. We also discuss the possibility of hypertrophied claws working as honest aposematic signals or playing an important role as decoys.