High-model abundance may permit the gradual evolution of Batesian mimicry: an experimental test

Abstract

In Batesian mimicry, a harmless species (the 'mimic') resembles a dangerous species (the 'model') and is thus protected from predators. It is often assumed that the mimetic phenotype evolves from a cryptic phenotype, but it is unclear how a population can transition through intermediate phenotypes; such intermediates may receive neither the benefits of crypsis nor mimicry. Here, we ask if selection against intermediates weakens with increasing model abundance. We also ask if mimicry has evolved from cryptic phenotypes in a mimetic clade. We first present an ancestral character-state reconstruction showing that mimicry of a coral snake (Micrurus fulvius) by the scarlet kingsnake (Lampropeltis elapsoides) evolved from a cryptic phenotype. We then evaluate predation rates on intermediate phenotypes relative to cryptic and mimetic phenotypes under conditions of both high-and low-model abundances. Our results indicate that where coral snakes are rare, intermediate phenotypes are attacked more often than cryptic and mimetic phenotypes, indicating the presence of an adaptive valley. However, where coral snakes are abundant, intermediate phenotypes are not attacked more frequently, resulting in an adaptive landscape without a valley. Thus, high-model abundance may facilitate the evolution of Batesian mimicry.

A Predator's Perspective of the Accuracy of Ant Mimicry in Spiders

“…Here it is apparent that imprecise mimics, although not avoided to the same degree as accurate mimics, were nevertheless aversive to naïve predators, suggesting that learning is not essential for the same effects to be seen. A mutually compatible alternative explanation is simply that very numerous and very dangerous models may produce a wider "cone of protection," thus allowing for imprecise mimicry [34] because the payoff to a predator for attacking prey with a given resemblance to a numerous and highly noxious model is limited [35]. Furthermore, polymorphic mimics that do not resemble any particular ant species especially closely may gain other advantages.…”

Rapid evolution of mimicry following local model extinction

“…'edge sympatry') [7]. Field experiments have shown that selection for mimicry is strongest in edge sympatry [8]. Because the model is rare in edge sympatry (see above), the probability of mistakenly attacking it is low, and predators are therefore more willing to risk attacking imprecise mimics.…”

“…Greater mimetic precision may evolve after model extirpation if alternative prey are abundant, and if the fitness costs associated with mistaking a model for a mimic were historically greater than those associated with mistaking a mimic for a model (as might be the case with highly noxious models). Indeed, theoretical [13][14][15] and empirical studies [7,8] have shown that only the most precise mimics receive protection from predation when the model becomes increasingly rare (as would be expected to occur when model extirpation is imminent); thus, selection may continue to favour the evolution of more refined mimicry, even after the model is gone.…”

“…Batesian mimicry occurs when an edible species (the 'mimic') evolves to resemble a conspicuous, noxious species (the 'model'), thereby gaining protection from predation [3][4][5]. The degree of resemblance between mimics and their models is generally sensitive to changes in model abundance [5,6]; mimetic fidelity can decrease or increase, depending on whether the model becomes relatively more or less abundant, respectively [7,8].…”

Natural Selection and Multiple Realisation: A Closer Look

“…Ridley, 1995). So, for instance, when biologists speak of Batesian mimicry they intend cases where "...a harmless species (the 'mimic') resembles a dangerous species (the 'model') and is thus protected from predators" (Kikuchi andPfennig 2010, 1041). This characterisation is then taken to capture what is important as for the evolution of such traits, while being silent on the exact realisation.…”