Can dietary conservatism explain the primary evolution of aposematism?

Abstract

Predators are often unwilling to eat prey with novel appearances (so called dietary conservatism). It has repeatedly, although controversially, been argued that such wariness can contribute to the evolution of bright coloration in prey animals with effective secondary defences such as toxins. In this paper we report the results of novel evolutionary simulations in which bright prey emerge in otherwise cryptic, defended populations, and predators vary in their level of dietary wariness. A novel prediction from our simulations is that rare aposematic prey can evolve to a dynamic equilibrium with their cryptic conspecifics, and persist for long evolutionary timescales without ever reaching fixation in prey populations. Furthermore, we show that when conditions are more beneficial for new aposematic forms, for example because there are many palatable prey in a habitat, then dietary conservatism can indeed explain the evolution of aposematism, but the generality of this result was considerably restricted by variation in levels of dietary conservatism seen within predator populations and by increased predator longevity. We use the results to consider the case that ‘receiver biases’ could explain aposematism, rather than recently suggested models of signal reliability.