Disruptive Selection

Definition

Disruptive selection is a type of natural selection that favors extreme variations of traits over intermediate variations, leading to a divergence in phenotypes within a population. This process can contribute to the formation of new species by promoting reproductive isolation among groups with differing adaptations, which enhances biodiversity. Disruptive selection is crucial in the context of evolution, as it highlights how environmental pressures can shape genetic diversity and adaptations in ways that deviate from the norm.

5 Must Know Facts For Your Next Test

1. Disruptive selection can occur when a population is exposed to varying environmental conditions that favor extreme phenotypes, such as light and dark colors in animals living in a patchy habitat.
2. This form of selection often leads to increased genetic diversity within a population as it encourages the survival of multiple distinct phenotypes.
3. Disruptive selection may play a significant role in adaptive radiation, where a single ancestral species rapidly evolves into multiple new forms adapted to different environments.
4. It can also lead to reproductive isolation, as individuals with extreme traits may mate preferentially with similar individuals, driving divergence in traits over time.
5. Examples of disruptive selection can be observed in species like African seedcracker finches, where birds with either very large or very small beaks are favored due to their ability to exploit different food sources.

Review Questions

• How does disruptive selection differ from stabilizing and directional selection in terms of its impact on phenotypic variation within a population?
  • Disruptive selection differs from stabilizing selection and directional selection by favoring extreme phenotypes while selecting against intermediate forms. In stabilizing selection, the average phenotype is favored, reducing variation, whereas directional selection favors one extreme trait, pushing the population toward that end. Disruptive selection promotes diversity by allowing multiple distinct phenotypes to thrive under varying environmental pressures, leading to a potential increase in speciation events.
• What role does disruptive selection play in the process of speciation and how can it lead to reproductive isolation?
  • Disruptive selection plays a significant role in speciation by promoting divergent traits among populations that occupy different niches or environments. As individuals with extreme traits become better adapted to their specific environments, they may begin to prefer mating with others that share those traits. Over time, this preference can lead to reproductive isolation between groups with differing adaptations, ultimately resulting in the emergence of new species.
• Analyze a real-world example of disruptive selection and explain how it demonstrates the principles of natural selection and adaptation.
  • A classic example of disruptive selection can be seen in the African seedcracker finch, where birds with either very large or very small beaks are favored over those with medium-sized beaks. This variation allows them to exploit different types of seeds available in their environment—larger beaks for hard seeds and smaller beaks for softer seeds. This scenario illustrates natural selection as the finches adapt to their ecological niches; over time, this selective pressure leads to increased differences between these two groups and highlights how adaptations can arise through disruption of an average trait.

Related terms

Natural Selection:

The process by which individuals with favorable traits are more likely to survive and reproduce, thereby passing those traits to the next generation.

Phenotype: The observable characteristics or traits of an organism, which result from the interaction of its genotype with the environment.

Speciation: The evolutionary process through which new biological species arise, often as a result of disruptive selection and reproductive isolation.