Disruptive Selection

Definition

Disruptive selection is a type of natural selection that favors individuals at both extremes of a trait distribution while selecting against the average or intermediate phenotypes. This process can lead to increased genetic variance and may promote speciation, especially when the extremes have distinct advantages in their environment. Over time, disruptive selection can contribute to the emergence of new species by enhancing ecological divergence and altering allele frequencies in populations.

5 Must Know Facts For Your Next Test

1. Disruptive selection can lead to the development of two or more distinct phenotypes in a population, increasing diversity.
2. It is often observed in environments that contain heterogeneous habitats where different traits provide advantages in different niches.
3. This type of selection may increase the likelihood of speciation by driving populations apart as they adapt to their specific environments.
4. Disruptive selection can result in bimodal distribution of traits, where individuals cluster around two extreme phenotypes rather than a single average phenotype.
5. Examples of disruptive selection can be seen in African seedcracker birds, where individuals with either very large or very small beaks are favored due to their feeding on different types of seeds.

Review Questions

• How does disruptive selection differ from stabilizing and directional selection in terms of its impact on trait distribution within a population?
  • Disruptive selection differs from stabilizing and directional selection primarily in its effect on trait distribution. While stabilizing selection favors intermediate phenotypes and reduces variation, and directional selection favors one extreme phenotype over others, disruptive selection enhances variation by favoring both extremes. This results in a bimodal distribution where two distinct groups emerge, potentially leading to increased diversity within the population.
• Discuss how disruptive selection can contribute to speciation and ecological divergence within populations.
  • Disruptive selection contributes to speciation by promoting ecological divergence between populations as they adapt to different environments. By favoring individuals at both extremes of a trait spectrum, it creates distinct groups that may exploit different ecological niches. Over time, these adaptations can lead to reproductive isolation as the two groups evolve separately, ultimately resulting in the formation of new species.
• Evaluate the role of environmental factors in facilitating disruptive selection and providing examples from nature.
  • Environmental factors play a crucial role in facilitating disruptive selection by creating conditions where different traits provide advantages for survival and reproduction. For instance, in environments with varied food sources, such as different seed types for birds, individuals with extreme traits (like large or small beaks) are favored based on their ability to access these resources effectively. Such selective pressures drive populations toward adaptive changes that enhance their fitness in their specific ecological niches.

Related terms

Natural Selection:

A fundamental mechanism of evolution where organisms better adapted to their environment tend to survive and produce more offspring.

Ecological Niche:

The role or function of an organism or species within its ecosystem, including its habitat, resource use, and interactions with other organisms.

Adaptive Radiation:

The evolutionary process in which an ancestral species rapidly diversifies into a wide variety of forms to adapt to different environments.