Data from: Dissolved organic carbon and unimodal variation in sexual signal coloration in mosquitofish: a role for light limitation?

Natural selection plays an important role in the evolution of sexual
communication systems. Here, we assess the effect of two well-known
selection agents, transmission environment and predation, on
interpopulation variation in sexual signals. Our model system is a series
of 21 populations of Bahamian mosquitofish subjected to independent
variation in optical conditions and predation risk. We show that optically
diverse environments, caused by locally variable dissolved organic carbon
concentrations, rather than spatial variation in predation, drove
divergence in fin coloration (fin redness). We found a unimodal pattern of
phenotypic variation along the optical gradient indicating a
threshold-type response of visual signals to broad variation in optical
conditions. We discuss evolutionary and ecological mechanisms that may
drive such a pattern as well as the implications of non-monotonic clines
for evolutionary differentiation.