Negative Frequency-dependent Selection
The first explicit statement of frequency dependent selection appears to have been by E.B. Poulton in 1884 with reference to the way that predators could maintain color polymorphisms in their prey.
Perhaps the best known early modern statement of the principle in the twentieth century was the discussion by Bryan Clarke of apostatic selection (a synonym of negative frequency-dependent selection). In this paper, Clarke discussed frequency-dependent selection particularly with regard to predator attacks on polymorphic British snails, citing Luuk Tinbergen's classic work on searching images as support that predators such as birds would tend to specialize on common forms of palatable species. Clarke later became a major promoter of the idea that frequency-dependent balancing selection might explain abundant molecular polymorphisms (often in the absence of heterosis) in opposition to the neutral theory of molecular evolution.
Another example of negative frequency-dependent selection is in the case of plant self-incompatibility alleles. When two plants share the same incompatibility allele, they are unable to mate. Thus, a plant with a new (and therefore, rare) allele has more success at mating, and its allele spreads quickly through the population.
Negative frequency-dependent selection also operates in the interaction of many human pathogens, such as the flu virus. Once a particular strain has been common in a human population, most individuals would have developed an immune response to that strain. But a rare, novel strain of the flu virus would be able to spread quickly to almost any individual. This advantage of genetic novelty causes continual evolution of viral strains, with new versions common each year.
Another immune-related example of negative frequency-dependent selection is the major histocompatibility complex (MHC), which is involved in the recognition of foreign antigens and cells.) Frequency-dependent selection may explain the high degree of polymorphism of MHC.
In behavioral ecology, negative frequency-dependent selection is often responsible for maintaining multiple behavioral strategies within a species. For example, male common side-blotched lizards have three morphs, which either defend large territories and maintain large harems of females, defend smaller territories and keep one female, or mimic females in order to sneak matings from the other two morphs. These three morphs participate in a rock paper scissors sort of interaction such that no one morph completely outcompetes the other two. Another example occurs in the Scaly-breasted Munia, where certain individuals become scroungers and other individuals become producers.
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