Apostatic selection

Apostatic selection is negative frequency-dependent selection. It describes the survival of individual prey animals that are different (through mutation) from their species in a way that makes it more likely for them to be ignored by their predators. It operates on polymorphic species, species which have different forms. In negative frequency-dependent selection, the common forms of a species are preyed on more than the rarer forms, giving the rare forms a selective advantage in the population.

Apostatic selection was used in 1962 by Bryan Clarke in reference to predation on polymorphic grove snails and since then it has been used interchangeably with negative frequency-dependent selection.

Apostatic selection can also apply to the predator if the predator has various morphs. There are multiple concepts that are closely linked with apostatic selection. One is the idea of prey switching, which is another term used to look at a different aspect of the same phenomenon, as well as the concept of a 'search image'. Apostatic selection is important in evolution because it can sustain a stable equilibrium of morph frequencies, and hence maintains large amounts of genetic diversity in natural populations.

Prey switching is the concept that predators sometimes switch from primary prey to an alternative food source for various reasons. This is related to apostatic selection because when a rare morph is being selected for, it is going to increase in abundance in a specific population until it becomes recognized by a predator. Prey switching, therefore, seems to be a result of apostatic selection. Prey switching is related to prey preference as well as the abundance of the prey.

The concept of a ‘search image’ in predatory birds is that they only look for a single cryptic food even though there are other cryptic alternatives that may be as equally beneficial. A search image defined by Luuk Tinbergen as a typical image of a prey that a predator can remember and use to spot prey when that image is common. Having a search image can be beneficial because it increases proficiency of a predator in finding a common morph type.

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