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

Abstract

The ability of organisms to change colour in response to a change in environmental conditions is widespread across taxa. Predation represents the longstanding hypothesis for the evolution of such colouration plasticity. Yet, tests of the evolutionary drivers of colouration plasticity remain rare. Here, we examine how predation shapes both baseline colouration and colouration 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 hypothesised that fish from high-predation sites would exhibit lighter baseline colouration due to associations with open canopy and increased light, and that predators would select for stronger plasticity in background-induced colour change. Our results did reveal hypothesised shifts in baseline colouration with high-predation fish generally lighter. A. hartii also displayed strong plasticity, darkening on black backgrounds and lightening on white. However, the effect of predation on baseline colour and colouration 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 colouration plasticity and that local ecological factors that covary with predators may also exert selection on body colour.