Disruptive Selection

Definition

Disruptive selection is a type of natural selection that favors extreme phenotypes over intermediate phenotypes within a population. This process can lead to increased diversity as individuals at both ends of the trait spectrum have higher fitness than those with average traits. Over time, disruptive selection can contribute to speciation by promoting the development of distinct groups within a population that adapt to different ecological niches.

5 Must Know Facts For Your Next Test

1. Disruptive selection can occur in environments where two or more distinct resources are available, favoring individuals that exploit these different resources.
2. This form of selection is often observed in populations where individuals exhibit two different color morphs or sizes that have specific advantages in their environment.
3. Disruptive selection can lead to increased genetic variation within a population, as it supports the survival of diverse traits rather than a single optimal trait.
4. It is different from stabilizing selection, which favors intermediate phenotypes and reduces variation in a trait.
5. In some cases, disruptive selection can drive speciation, particularly when populations become geographically isolated and adapt to their unique environments.

Review Questions

• How does disruptive selection differ from stabilizing selection in terms of its effects on a population's phenotype distribution?
  • Disruptive selection promotes extreme phenotypes and reduces the frequency of intermediate traits, creating a bimodal distribution of phenotypes within the population. In contrast, stabilizing selection favors intermediate traits and eliminates extremes, leading to a more uniform phenotype distribution. While disruptive selection increases variation by supporting diverse traits, stabilizing selection decreases variation by selecting for traits that are average or moderate.
• Discuss an example of a real-world scenario where disruptive selection might occur and its implications for the population involved.
  • One classic example of disruptive selection occurs in African seedcracker birds, where birds with either very large or very small beaks have a feeding advantage depending on the type of seeds available. Those with intermediate-sized beaks struggle to efficiently crack either type of seed. As a result, this selective pressure leads to increased specialization among the birds and could eventually contribute to speciation as these two groups adapt to their respective food sources.
• Evaluate the potential long-term evolutionary consequences of disruptive selection on a population's genetic diversity and speciation rates.
  • In the long term, disruptive selection can significantly increase genetic diversity within a population by favoring multiple phenotypes that adapt to different ecological niches. This greater diversity enhances the likelihood of speciation as subpopulations may become increasingly distinct due to differing selective pressures. Over time, if these subpopulations experience reproductive isolation, they may evolve into entirely new species, contributing to biodiversity. Thus, disruptive selection plays a crucial role in shaping evolutionary trajectories by fostering both variation and divergence among populations.

Related terms

Natural Selection: The process through which individuals with advantageous traits are more likely to survive and reproduce, leading to the gradual evolution of a species.

Phenotype: The observable physical or behavioral traits of an organism, which result from the interaction of its genetic makeup and environment.

Speciation:

The evolutionary process by which populations evolve to become distinct species, often as a result of genetic divergence and reproductive isolation.