Disruptive selection

Definition

Disruptive selection is a type of natural selection that favors extreme traits over intermediate traits within a population. This process can lead to increased variation in a population and may contribute to speciation, as individuals with extreme characteristics are more likely to survive and reproduce in changing environments or diverse ecological niches.

5 Must Know Facts For Your Next Test

1. Disruptive selection can create a bimodal distribution of traits in a population, leading to two or more distinct phenotypes.
2. This type of selection is often observed in environments that offer multiple niches, where different extremes may be favored depending on resource availability.
3. Disruptive selection can accelerate the process of speciation by promoting reproductive isolation between the extreme trait bearers and those with intermediate traits.
4. An example of disruptive selection is seen in African seedcracker finches, where birds with either very large or very small beaks are favored due to their ability to exploit different food sources.
5. Over time, disruptive selection can lead to genetic divergence as the extremes adapt to their specific niches, potentially resulting in the formation of new species.

Review Questions

• How does disruptive selection differ from stabilizing and directional selection in terms of its impact on trait distribution?
  • Disruptive selection differs from stabilizing selection, which favors intermediate traits and reduces variation, and directional selection, which favors one extreme trait over the other. In disruptive selection, both extremes are favored, creating a bimodal distribution where individuals with extreme traits have a higher survival rate. This leads to increased variability in traits within the population and can set the stage for speciation as intermediate trait bearers may be at a disadvantage.
• Discuss an example of how disruptive selection can lead to speciation in a specific population.
  • A clear example of disruptive selection leading to speciation can be seen in the case of the African cichlid fish. In certain lakes, these fish exhibit a range of jaw sizes suited for feeding on different types of prey. As larger and smaller jawed fish thrive while those with average-sized jaws struggle, this results in two distinct feeding strategies emerging. Over time, this could lead to reproductive isolation between these two groups as they adapt to their specialized diets, eventually resulting in the formation of new species.
• Evaluate the role of environmental factors in influencing disruptive selection and the implications for biodiversity.
  • Environmental factors play a crucial role in driving disruptive selection by determining which traits confer advantages under specific conditions. For instance, in habitats where resource availability is heterogeneous, individuals with either extreme traits may be better suited to exploit different resources. This not only enhances phenotypic diversity but also promotes adaptive radiations as populations diversify into various ecological niches. The result is an increase in biodiversity as more species evolve to fill specific roles within the ecosystem, highlighting the interconnectedness of environment and evolutionary processes.

Related terms

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

Speciation: The evolutionary process by which populations evolve to become distinct species, often as a result of isolation and divergent natural selection.

Phenotypic variation: The observable differences in physical traits among individuals within a population, which can be influenced by genetic and environmental factors.