Honest Signaling and the Uses of Prey Coloration

Although signal reliability is of fundamental importance to the understanding of animal communication, the extent of signal honesty in relation to antipredator warning signals has received relatively little attention. A recent theoretical model that assumed a physiological linkage between pigmentation and toxicity suggested that (aposematic) warning signals may often be reliable, in the sense that brightness and toxicity are positively correlated within prey populations. Two shortcomings of the model were (1) the requirement among predators for an innate aversion to brightly colored prey and (2) the assumption that prey can generate only bright coloration and not cryptic coloration. We evaluated the generality of predictions of reliable signaling when these shortcomings were removed. Without innate avoidance of bright prey, we found a positive brightness-toxin correlation when conspicuous prey coloration provided an additional fitness benefit unrelated to predation. Initially, this correlation could evolve for reasons unrelated to prey signaling; hence, aposematism might represent a striking example of exaptation. Given a choice between using pigmentation for bright or for cryptic coloration, crypsis was favored only in conditions of very low or very high resource levels. In the latter case, toxicity correlated positively with degree of cryptic coloration. Predictions of toxin-signal correlation appear robust, but we can identify interesting conditions in which signal reliability is not predicted.