One cost of being gold : selective predation and implications for the maintenance of the Midas cichlid colour polymorphism (Perciformes: Cichlidae)

Abstract

In the colour-polymorphic Midas cichlid fish species complex (Amphilophus citrinellus spp.), gold morphs occur at much lower frequencies (< 10%) than dark individuals. This might be surprising because gold coloration is dominant and coded for by a single Mendelian locus. Furthermore, gold individuals are considered to be competitively advantaged over dark ones because they grow faster and win aggressive encounters more often compared to dark individuals of equal size. However, one might expect a cost of being gold in terms of natural selection as a result of predation. We tested whether the Jaguar cichlid (Parachromis managuensis), a major fish predator of Midas cichlids, preys differentially on colour variants of goldfish (Carassius auratus auratus), which were used as a proxy for Midas cichlids because of their similarity in colour. Size-matched pairs of prey fish (gold and dark) were offered to the predator and the time until the fish were attacked was recorded. The gold morph was attacked first more often (approximately 70%) but not faster than the dark morph. This suggests that the predator perceives the gold individual first, and/or that the predator exhibits a preference or higher motivation to attack the gold prey fish. The increased risk of predation of gold prey fish suggests for the Midas cichlid system that being gold may carry significant costs in terms of natural selection as a result of its major piscivorous predator.