Disruptive selection

Disruptive selection, also known as diversifying selection, is a type of natural selection that simultaneously favors individuals at both extremes of the distribution over individuals with intermediate phenotypes. This evolutionary process is significant because it can lead to the emergence of new species through speciation, particularly when the environmental conditions support multiple phenotypes.

In disruptive selection, environmental conditions or ecological niches allow individuals with extreme traits to have a higher fitness compared to those in the middle of the trait spectrum. This can result in a bimodal distribution of traits within a population, where the two extremes become more common and the intermediate forms are less common or even eliminated.

Mechanism

The mechanism of disruptive selection involves different factors that can influence the fitness of individuals within a population. These factors include but are not limited to, predation, competition for resources, and habitat specialization. For example, in a habitat where resources are available in two distinct forms, individuals specialized in exploiting one or the other resource form may have a survival advantage over those that are not specialized.

Examples

One classic example of disruptive selection is the case of the Galápagos Islands' finches, studied by Charles Darwin. In environments where medium-sized seeds were scarce but small and large seeds were abundant, finches with either particularly large or small beaks had a survival advantage over those with medium-sized beaks. This led to an increase in the frequency of both large and small beaked birds, while medium-sized beaked birds became less common.

Another example can be found in certain species of butterflies, where individuals with either very pale or very dark wing colors are favored in certain habitats, but those with intermediate colors are more easily preyed upon.

Consequences

The consequences of disruptive selection can be profound, leading to increased genetic diversity within a population and potentially the formation of new species. If the diverging subpopulations become reproductively isolated, for instance, through geographic isolation or differences in mating behavior, this can lead to allopatric speciation or sympatric speciation, respectively.

See also

• Directional selection
• Stabilizing selection
• Sexual selection
• Artificial selection