The main difference between stabilizing selection and disruptive selection is that stabilization selection favors the average or intermediate phenotype in a population and acts against extreme variations. In contrast, disruptive selection favors the extreme phenotypes of a trait over the intermediate or average phenotypes.
Stabilizing and disruptive selection are two different types of natural selection that can affect the distribution of traits within a population.
Key Areas Covered
1. What is Stabilizing Selection
– Definition, Features, Variations
2. What is Disruptive Selection
– Definition, Features, Variations
3. Similarities Between Stabilizing Selection and Disruptive Selection
– Outline of Common Features
4. Difference Between Stabilizing Selection and Disruptive Selection
– Comparison of Key Differences
Key Terms
Disruptive Selection, Diversifying Selection, Stabilizing Selection
What is Stabilizing Selection
Stabilizing selection is a type of natural selection that attempts to maintain the average or intermediate phenotype within a population while reducing the occurrence of extreme variations. It is a fundamental mechanism that helps preserve certain traits’ stability and consistency over time. This process occurs when individuals with phenotypic traits close to the population mean have higher fitness than individuals with extreme phenotypes. As a result, the genetic diversity within the population is reduced, and the population becomes more homogenous in terms of the selected trait.
The driving force behind stabilizing selection is the selective pressure against extreme phenotypes. This pressure can arise from various factors such as environmental conditions, predation, or the functional requirement of a specific niche. By favoring individuals with average or intermediate phenotypes stabilizing selection ensures that the population remains well-adapted to its current ecological niche. Moreover, traits that are subject to stabilizing selection tend to be those that are optimal within the current environmental conditions.
A classic example of stabilizing selection can be observed in human birth weight. Extremely low birth weights are associated with increased health risks and infant mortality, while extremely high birth weights can lead to complications during childbirth. As a result, there is a selective advantage for babies with intermediate birth weights. This selection pressure acts to reduce the occurrence of both extremely low and extremely high birth weights, maintaining the population within a range of optimal birth weights.
Stabilizing selection can also be seen in various other traits across different organisms. For instance, clutch size in birds is subjected to stabilizing selection.
What is Disruptive Selection
Disruptive selection, also known as diversifying selection, is a type of natural selection that favors the extreme phenotypes of a trait over the intermediate or average phenotypes. Unlike stabilizing selection, which maintains the population around a mean phenotype, disruptive selection acts to increase the genetic variation within a population by favoring individuals at both ends of the phenotypic spectrum. This process can lead to the emergence of distinct subpopulations or the evolution of new species.
Disruptive selection occurs when different extreme phenotypes have higher fitness than individuals with intermediate phenotypes. This can be driven by various factors such as environmental heterogeneity, resource partitioning, or the need to exploit different niches. Disruptive selection promotes divergence and specialization within a population by favoring extreme phenotypes.
Disruptive selection can also occur in response to different ecological pressures. For example, in a habitat with varying predation risk levels, a prey species population may exhibit disruptive selection for different camouflage strategies. Individuals with a high degree of cryptic coloration that allows them to blend into the background effectively may have a higher survival rate when predation risk is low.
Effects of Disruptive Selection on Population
Disruptive selection can lead to the divergence of a population into distinct subpopulations or even the formation of new species. When disruptive selection acts on a trait associated with reproductive isolation, such as mate preference or habitat preference, it can lead to the evolution of distinct groups reproductively isolated from each other. Over time, these isolated groups may accumulate further genetic and phenotypic differences, eventually becoming separate species.
Secondly, disruptive selection can increase genetic variation within a population. By favoring extreme phenotypes, disruptive selection promotes the persistence of genetic variants at both ends of the phenotypic spectrum. This can enhance the adaptive potential of a population, allowing it to respond more effectively to changing environmental conditions or new ecological opportunities.
Similarities Between Stabilizing Selection and Disruptive Selection
- Stabilizing selection and disruptive selection exert selective pressure on a population’s phenotypic traits.
- Both stabilizing and disruptive selection can influence the level of genetic variation within a population.
- The need for adaptation to specific environmental conditions drives both types of selection.
Difference Between Stabilizing Selection and Disruptive Selection
Definition
Stabilization selection favors a population’s average or intermediate phenotype and acts against extreme variations. In contrast, disruptive selection favors individuals at both extremes of the phenotypic range, while individuals with intermediate traits are selected against.
Selection Pressure
Stabilizing selection favors individuals with intermediate phenotypes and acts against extreme phenotypes. In contrast, disruptive selection favors extreme phenotypes and acts against intermediates.
Trait Distribution
Moreover, stabilizing selection leads to a narrower trait distribution within a population, but disruptive selection leads to a broader trait distribution.
Genetic Variation
Stabilizing selection reduces genetic variation within a population over time. Disruptive selection, however, promotes genetic variation within a population.
Conclusion
Stabilizing selection and disruptive selection are two different types of natural selection that can affect the distribution of traits within a population. The main difference between stabilizing selection and disruptive selection is that stabilization selection favors the average or intermediate phenotype in a population and acts against extreme variations. In contrast, disruptive selection favors the extreme phenotypes of a trait over the intermediate or average phenotypes.
Reference:
1. “Stabilizing Selection.” Biology Dictionary Online.
2. “Disruptive selection and then what?” Science Direct.
Image Courtesy:
1. “Stabilizing selection” By BoH – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “Selection Types Chart” By Azcolvin429 – Own work (CC BY-SA 3.0) via Commons Wikimedia
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