Automimicry

Automimicry is a kind of intraspecific mimicry, meaning that it occurs within a single species of animal. In automimicry, not all members of a defended, aposematic species are defended to the same degree; some may actually be so weakly defended that they do not deter predators that attack them at all. These weakly defended individuals are parasitic on other members of their species to provide the negative reinforcement learning that required for warning signals to function.

Automimicry was first reported by the ecologist Lincoln P. Brower, who found that monarch butterflies (Danaus plexippus) reared on cabbage (Brassica oleracea) were palatable to blue jays (Cyanocitta cristata bromia). However, monarchs raised on their natural host plant, milkweed (Asclepias curassavica) were noxious to jays - in fact, jays that ingested them vomited. Subsequently, Brower put forth the hypothesis of automimicry, in which a polymorphism within a species existed: some individuals might be defended, and others palatable. Many groups of animals have since been shown to obtain toxic compounds through their diets, making automimicry potentially widespread. Even if toxic compounds are produced by metabolic processes with an animal, there may still be variability in the amount that animals invest in them, so scope for automimicry remains even when dietary plasticity is not involved. Whatever the mechanism, palatability may vary with age, sex, or how recently they used their supply of toxin.

The existence of automimicry poses two challenges to evolutionary theory: how can automimicry be maintained, and how can automimicry evolve? For the first question, as long as prey of the species are, on average, unprofitable for predators to attack, automimicry can persist. If this condition is not met, then the population of the species rapidly crashes. The second question is more difficult, and can also be rephrased as being about the mechanisms that keep warning signals honest. If signals were not honest, they would not be evolutionarily stable. If costs of using toxins for defence affects members of a species, then cheats might always have higher fitness than honest signallers defended by costly toxins.

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