Non-parallel impacts of predators on the evolution of coloration plasticity in Trinidadian killifish

The ability of organisms to change color in response to a change in environmental conditions is widespread across taxa. Predation represents the longstanding hypothesis for the evolution of such coloration plasticity. Yet, tests of the evolutionary drivers of coloration plasticity remain rare. Here, we examine how predation shapes both baseline coloration and coloration plasticity in the Trinidadian killifish (Anablepsoides hartii). This species inhabits streams that vary in fish predator presence, creating a replicated natural experiment across three rivers. We hypothesized that fish from high-predation sites would exhibit lighter baseline coloration due to associations with open canopy and increased light, and that predators would select for stronger plasticity in background-induced color change. Our results did reveal hypothesized shifts in baseline coloration with high-predation fish generally lighter. Anablepsoides hartii also displayed strong plasticity, darkening on black backgrounds and lightening on white. However, the effect of predation on baseline color and coloration plasticity was inconsistent across rivers, suggesting that additional ecological factors also contribute to these responses. Our study provides empirical evidence that predators are not the sole driver of variation in coloration plasticity and that local ecological factors that covary with predators may also exert selection on body color.