Environmental variation promotes colour morph-specific behavioural differences in a cichlid fish

Colour polymorphisms are among the most striking examples of intraspecific variation. If vulnerability in a given habitat depends on body colour, heterogeneity in the environment may drive behavioural differences between differently coloured individuals. We tested this prediction in a colour-polymorphic fish species, the red devil, Amphilophus labiatus. In Amphilophus cichlids, ‘dark’ and ‘gold’ morphs have previously been linked to differences in morphology, aggressive behaviour and mate choice, but it is unknown whether the morphs also differ in other key behaviours, or whether any such differences are sensitive to environmental factors. By testing activity, boldness and exploration, our laboratory experiment provided moderate evidence for an environmental variable, substrate type, having colour morph-specific effects on behaviour: dark morph red devils explored their environment more extensively when the environmental background (substrate) was dark brown than when it was light coloured, whereas gold morph individuals did not differ in their behaviour in relation to substrate colour. These results show that environmentally driven behavioural differences may be context dependent and have a role in maintaining colour morph-specific behavioural strategies. Hence, the evolution of morphological traits, such as colour morphs, cannot be fully understood without considering the behavioural phenotypes that have coevolved with them in interaction with the environment.