Behaviour: A damselfish can change its false eyespots

Young Ambon damselfish that are exposed to predators tend to develop larger false eyespots, as well as undergoing a corresponding reduction in the growth of their eyes. The research, published in Scientific Reports this week, suggests that eyespot size may be plastic and can evolve to suit certain environmental conditions.

Many fishes and terrestrial insects sport false eyespots: large dark circles surrounded by a lightly coloured ring, mimicking the appearance of a vertebrate eye. Ambon damselfish (Pomancentrus amboinensis) make their home on the Great Barrier Reef, where they are highly vulnerable to predation. Juveniles have a lightly coloured body and a conspicuous eyespot on the upper rear fin, which fades away as the animal approaches maturation. Oona Lonnstedt and colleagues show that the size of these eyespots can increase upon exposure to predators, a change that is accompanied by reduced growth of the damselfish’s eyes. Damselfish that were exposed to predators seemed to experience higher survival rates compared to those exposed to herbivores or those isolated from other fish, the findings reveal.

The study suggests that false eyespots may represent a short-term adaptation to the presence of predators, potentially functioning to misdirect predator strikes and/or to protect the head region from fatal attacks. The results hint at the importance of experience with predators to prey survival early in life.