Inbreeding and Competitor’s Genetic Relatedness Affect Dynamic Male Color Ornament Expression in a Cichlid Fish

AbstractOrnamental traits signaling phenotypic and/or genetic quality play a central role in sexual selection and greatly determine the access to mating partners and thus fitness. Accordingly, they underlie strong directional selection. Ornament expression is often condition dependent and therefore supposed to be sensitive to inbreeding. Kin selection theory predicts that ornament expression may depend on the genetic relatedness of competitors. Here, we examined the dynamic color expression in male groups of the cichlid <i>Pelvicachromis taeniatus</i> during competition over breeding sites. Groups (trios) were either inbred or outbred, and each consisted of two unfamiliar brothers and an unfamiliar unrelated male. Males of <i>P. taeniatus</i> are territorial and develop a carotenoid-based yellow coloration at the ventral body region and the caudal fin. Intense body coloration signals dominance. Our study showed (i) that outbred males generally developed more intense yellow coloration (chromaticity) during the experiment compared with inbred males and (ii) that related males were more intensively colored at the caudal fin after the trials than the unrelated males. In conclusion, our study indicates environment-dependent inbreeding depression in a male ornament as well as positive kin-selected effects on ornament expression. Our study describes understudied sources of phenotypic variation in ornamental traits in animals.