On the spot: the absence of predators reveals eyespot plasticity in a marine fish

Abstract

Eyespots have long been thought to confer protection against predators, but empirical evidence demonstrating the effectiveness of these markings and their survival value in the wild is limited. Using a mark–recapture experiment, I examined the functional significance of the eyespot on the dorsal fin of a juvenile tropical fish to its survival on coral reefs. None of the juveniles recaptured 1 month after settlement showed evidence of bite marks on the posterior region of the bodies to suggest a deflective function of their eyespot. When I compared the survivors with recruits from the same settlement cohort, I detected no change in the frequency distribution of eyespot size, suggesting no selective pressure operating on this trait. I compared these survivors with conspecifics from the same cohort collected at settlement and then outgrown in the absence of predators under 3 food regimes and 2 levels of intraspecific competition. I found that the eyespots of wild juveniles were larger overall than those of conspecifics maintained in a predator-free environment. The results of this study indicate that larger eyespots per se do not confer a survival advantage in the wild, suggesting that eyespots of this species may not have the long-assumed antipredatory function but play a role in interactions with adult conspecifics. I suggest that juveniles maintain eyespots even when predators or adult conspecifics are absent because they can be afforded at very low costs and may still be beneficial to their bearer under specific ecological conditions.