The evolution of darter color and pattern: small, rocky streams and riffles enhance the diversification of bright and conspicuous fishes

Organismal color and pattern are important to numerous aspects of animal fitness and may impact species divergence. Whether different environmental conditions may impact rates of color diversification, and the subsequent impacts on lineage diversification, has not been well studied. We investigated the evolution of color and pattern in Darters (Etheostomatinae; Percidae), a species-rich clade of freshwater fishes showing a remarkable diversity in color. Using recently developed approaches in color and pattern analysis, we quantified color and pattern attributes in 122 species. We applied multivariate statistics and phylogenetic comparative methods to investigate the relationship between river habitat (drainage area, elevation, slope, substrate, etc), darter color characteristics and changes in the rate of color evolution. We found color attributes were significantly related to river habitat, and rates of color evolution differed between macro- and micro-habitat categories; smaller streams and riffles in particular were associated with the rapid evolution of conspicuous and complex color patterns. We suggest that these differences are consistent with tradeoffs in predator abundance and photic environment. Small river habitats may facilitate rapid evolution of species-specific color patterns and reinforce divergence in secondary sympatry.