Predator preference for brightly colored males in the guppy: a viability cost for a sexually selected trait

Although conspicuous visual sexual signals, such as bright colors, in males serve to attract females in numerous species, they may also attract the attention of potential predators and thus may be costly in terms of increasing individual risk of mortality to predation. Most models of the evolution of extravagant male sexual traits and female preferences for them assume that the sexually preferred male trait is costly to produce and maintain. However, there is surprisingly little empirical evidence for direct fitness costs associated with sexually selected visual traits that enhance male mating success. In the present study, we report a direct fitness cost for sexually selected, bright body-color patterns in males in the form of an associated greater risk of mortality to predation. By using the guppy (Poecilia reticulata) and the blue acara cichlid fish (Aequidens pulcher) as a model prey-predator system, we demonstrate experimentally that individual cichlids preferentially and consistently approached, attacked, and captured the more brightly colored of two size-matched male guppies presented simultaneously in staged encounters. This resulted in the brightly colored male incurring, on average, a significantly higher risk of mortality given an encounter with the predator than with the drabber male in matched pairs. Our results constitute strong behavioral evidence for a direct viability cost associated with bright coloration in male guppies, and they corroborate the generally accepted paradigm that directional predation by visual fish predators against brightly colored, adult male guppies underlies the evolution of the known divergent color patterns in natural guppy populations that experience different intensities of predation. The viability cost associated with bright conspicuous coloration in male guppies potentially reinforces for females the reliability of this sexually selected trait as an indicator trait of male quality.