Female preference for male coloration may explain behavioural isolation in sympatric darters

Animal colour patterns are among the most striking examples of biological diversity. Elaborate coloration is thought to play a role in mate choice within populations and to pose a barrier to interbreeding between species, with individuals preferring the coloration of conspecifics. Ideally, the importance of coloration as a reproductive barrier would be tested by holding all traits constant and manipulating only colour to test its effect. In butterflies, researchers use paper models to manipulate female colour patterns and show strong male preference for conspecific female coloration. In African cichlids and poison frogs, researchers manipulate the light environment to test the importance of male colour in female preference for conspecifics. Here we use motorized models to test whether females in a pair of sexually dimorphic fish species (genus: Etheostoma) prefer conspecific over heterospecific male coloration. By isolating and manipulating specific components of male coloration, we show that females of both species significantly prefer conspecific male colour (red versus green) and pattern (stripe versus bars). These results provide strong evidence that female preference for conspecific male nuptial coloration may play a critical role in behavioural isolation.