The Evolution of Mimicry

Cryptic species have evolved camouflage, which enhances survival by decreasing their visibility and thus protecting them from would-be predators. Conversely, aposematic species have evolved vibrant colors which enhance visibility. These warning signals work by helping unpalatable, toxic, evasive, or stinging prey stand out from more favorable prey. Thus, predators learn to generalize the appearance of prey which taste bad or can inflict pain (Balogh 2005). Yet, all species with aposematic coloration do not have other unfavorable features. These species, known as Batesian mimics, have evolved to look like model species which are unprofitable to predators (Mappes 1997). Thus, Batesian mimicry enhances survival of otherwise unprotected species, while increasing the attack rate of the model species and deceiving the predator (Ritland 1991). As such, Batesian mimicry is part of an evolutionary exploitative relationship, in which the mimic derives benefit at the prey and predators expense. Conversely, Müllerian mimicry, in which two (or more) unfavorable prey species share similar physical characteristics, actually benefits all of the directly involved species. Since the co-mimics are unfavorable and similar in appearance, Müllerian mimics are less likely to be consumed by predators. The predators benefit because they do not have to suffer the consequences of consuming the unfavorable prey. Thus, Müllerian mimicry is a complex evolutionary mutualism which enhances survival of the involved prey and predators alike (Gavrilets 1997). There are many questions regarding the evolutionary pathway of mimicry which have not yet been elucidated. Two theories have been proposed to explain the pathway of Müllerian mimicry. The first theory, developed by Nicholson in 1927, is known as the two-step hypothesis. In this theory, evolution occurs first due to a large mutational change which causes a mimic to appear more similar to a model. After this large mutational change, the second step is a gradual change (Balogh 2005). Conversely, Fisher (1927) proposed the gradual hypothesis which is driven by predator generalization. This theory states that mimicry occurs from many small mutations each of which slightly increase the similarity between the mimic and the model. While eighty years have passed since these two theories were developed, the evolutionary path for Müllerian mimicry has still not been elucidated. Many other questions regarding the evolution of mimicry also still exist. For instance, the role of selective forces such as varying mortality rates among mimics and models in Batesian mimicry, population dynamics and associated ecological interactions, and the driving force for aposematic coloration have still not been elucidated. Furthermore, the role of imperfect mimicry, if any, in the evolution of mimicry has not been ____________________________________________