Colour differentiation in a coral reef fish throughout ontogeny: habitat background and flexibility

Colour polymorphism is widespread in animals but, in contrast to other types of polymorphism, has been little explored during ontogeny. Among coral reef fish, the surge damselfish Chrysiptera leucopoma settles in the larval stage as a yellow morph, whereas 2 colour morphs (yellow and brown) are apparent in adults at Rangiroa Atoll, French Polynesia. To understand this dimorphism, we tested, under controlled conditions, the hypotheses that: (1) environmental cues (habitat background and conspecific density) play important roles in morph differentiation during ontogeny and (2) morph colouration is reversible. Our first experiment showed that a dark habitat background induced the formation of the brown morph, while C. leucopoma larvae kept their yellow morph when placed in aquaria with a bright habitat background. Colour change from yellow to brown also occurred within the bright habitat, but only at high conspecific densities. Our second experiment showed that colour change was reversible within 15 d post-settlement, but not at the adult stage. Overall, our results highlighted that the studied polymorphism may be environmentally induced and reversible during the first post-settlement days of this coral reef fish.