The Sexually Dichromatic Use of Chromatophores for Cryptic Coloration in the Shrimp .

AbstractSexual dimorphism typically arises as a result of sexual selection or sex-specific natural selection. Species that exhibit cryptic coloration provide an excellent system for studying sex-specific selection for sexual dichromatism. In this study, we examined the sexually dichromatic use of chromatophores in the seawhip shrimp, (Borradaile, 1920), which commonly resides on colonies of (Lamarck, 1815), a gorgonian octocoral that occurs in multiple color morphs. We documented the frequency of cryptic coloration in and tested colony color preference in relation to their current color. In the field, individuals always matched the color of the colony they were found on or were largely translucent. However, when given a choice, individuals chose colonies at random, independent of color. Additionally, we quantified locations across the bodies of males and females that differ most in chromatophore usage and tested the ability of both sexes to change color over 7 days. Females housed with colonies that differed in color from their starting color changed their coloration over the 7 days to better match the colony, while males remained translucent regardless of the color of colony they were housed with. individuals differed most in their coloration in regions corresponding to the saddle region and areas of the abdomen, locations in which females carry their eggs during development. These findings provide insight into the ecological factors underlying sexual dichromatism and shed light on the potential sex-specific selective mechanisms responsible for sexually dimorphic traits.