The main difference between directional and disruptive selection is that directional selection favors a phenotype most fitted to the environment whereas disruptive selection favors extreme values for a trait over intermediate values. Furthermore, a single phenotype is selected in directional selection while more than one phenotypes are selected in disruptive selection.
Directional and disruptive (diversifying) selection are two types of mechanisms of natural selection, influencing the allele frequency of a population. Moreover, stabilizing selection is the third type of natural selection; in this selection, genetic diversity decreases as the population stabilizes on a particular trait value.
Key Areas Covered
1. What is Directional Selection
– Definition, Type of Natural Selection, Importance
2. What is Disruptive Selection
– Definition, Type of Natural Selection, Importance
3. What are the Similarities Between Directional and Disruptive Selection
– Outline of Common Features
4. What is the Difference Between Directional and Disruptive Selection
– Comparison of Key Differences
Key Terms
Allele Frequency, Directional Selection, Disruptive Selection, Natural Selection, Phenotypes
What is Directional Selection
Directional selection is a type of natural selection that leads to the selection of the phenotype that is most fitted to the environment. Therefore, environmental changes are the driving force of the directional selection. Moreover, as it selects a particular phenotype over its opposite phenotype, the existing variation moves towards one end. It occurs through the elevation of the allele frequency of the desired phenotype over generations.
Figure 1: Patterns of Natural Selection
Furthermore, the selection of dark-colored moths over light-colored moths is an example of directional selection. Prior to the industrial revolution, light-colored peppered moths were predominant. But, with the industrial revolution, the barks of trees became dark in color due to the soot spewing from factories. Then, light-colored moths were spotted very easily by predatory birds. Therefore, the amount of the dark-colored moths became increased as their darker coloration provided camouflage.
What is Disruptive Selection
Disruptive or diversifying selection is another type of natural selection mechanism responsible for the selection of extreme phenotypes over intermediate phenotypes. And, this type of selection mechanisms is commonly seen in animals with multiple male mating strategies. For example, in lobsters, the large alpha males that are dominant over the intermediate-sized males obtain mates by brute force.
Figure 2: Effect of Natural Selection Patterns
However, small males can sneak in for furtive copulations with females, along with the alpha males, within the same territory. Therefore, both alpha males that are large and other sneaking males that are small can survive. However, the intermediate-sized males that are unable to overtake alpha males and too big to sneak copulations will have less frequency to survive.
Similarities Between Directional and Disruptive Selection
- Directional and disruptive selection are two types of natural selection mechanisms.
- They are responsible for the selection of a particular phenotype over successive generations.
- Both increase the allele frequency of the favored phenotypes within the population.
- However, they may increase or decrease biological phenotypes within a population.
- The decrease in the number of phenotypes within a population reduces variation.
- Besides, both are responsible for producing individuals with greater evolutionary fitness.
- Moreover, they lead to adaptive evolution.
Difference Between Directional and Disruptive Selection
Definition
Directional selection refers to a mode of natural selection in which a single phenotype is favored, causing the allele frequency to continuously shift in one direction, while disruptive selection refers to a mode of natural selection in which extreme values for a trait are favored over intermediate values.
Significance
Thus, the main difference between directional and disruptive selection is that the directional selection is the selection of a particular phenotype that survives best in the environment while disruptive selection is the selection of extreme phenotypes over the intermediate phenotype.
Number of Phenotypes Selected
Moreover, directional selection selects a single phenotype while disruptive selection may select several extreme phenotypes. Hence, this is also a difference between directional and disruptive selection.
Variation
Another difference between directional and disruptive selection is that directional selection highly reduces the variation within the population while disruptive selection reduces variation only to a certain extent.
Examples
Selection of the dark-colored moths over light-colored moths after industrial evolution is an example of directional selection while selection of alpha males and “sneaking” males over intermediate males in a lobster population is an example of disruptive selection.
Conclusion
Directional selection is a mechanism of natural selection responsible for the selection of the phenotype most fitted to the environment over other phenotypes. It leads to an increase in the allele frequency of the selected phenotype within the population over time. On the other hand, disruptive selection is another mechanism of natural selection responsible for the selection of more than one extreme phenotypes over an intermediate phenotype. Here, more than one phenotypes can be selected. Therefore, the main difference between directional and disruptive selection is the type of phenotypes selected and their importance.
References:
1. “Adaptive Evolution|Boundless Biology.” Lumen, Available Here.
Image Courtesy:
1. “Patterns of Natural Selection” By Keith Chan – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “Selectiontypes-n0 images (vector)” By File:Selectiontypes-n0 images.png: Azcolvin429vectorisation: Mliu92 – File:Selectiontypes-n0 images.png (CC BY-SA 4.0) via Commons Wikimedia
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