The evolution and maintenance of Müllerian mimicry

Abstract Müllerian mimicry arises when unpalatable or otherwise unprofitable species evolve a similar appearance. While Batesian mimicry is widely considered to have evolved in palatable prey as a consequence of selection to deceive predators into believing that they are unpalatable, Müllerian mimicry is believed to have arisen as a consequence of selection to spread the burden of predator education through the adoption of a shared warning signal. Müllerian mimics are therefore considered mutualists, collectively reinforcing the protective value of their shared warning signals. We begin by discussing some examples of Müllerian mimicry that cannot be explained simply on the basis of shared ancestry. We then discuss Müller’s explanation in more depth, before presenting evidence that the shared resemblance has arisen for the reason that Müller hypothesized. Finally, we consider some of the predicted and observed properties of Müllerian mimicry systems in detail, including ecological and co-evolutionary phenomena, and consider some common questions that have only been partly resolved. We end by considering the connection between Batesian and Müllerian mimicry, arguing that like many natural systems, the nature of relationships can readily fluctuate from being parasitic to mutualistic and vice versa.