Disruptive Selection

Introduction

• Disruptive selection is a type of natural selection where extreme phenotypes at both ends of the phenotypic range are favoured.
• It can lead to the splitting or diversification of a population into two or more distinct phenotypic forms.

Example: Moth Camouflage

• Disruptive selection can be illustrated with the example of moths and their camouflage in different environments.

Moth Camouflage Scenario

• Consider an area with dark trees and areas of light lichen.
• Natural selection in this environment favours two distinct types of moths: a. High Melanin Moths: These moths have a lot of melanin and are well-camouflaged against the dark trees. b. Low Melanin Moths: These moths have very little melanin and blend effectively with the light-coloured lichen.

Intermediate Melanin Moths

• Moths with intermediate melanism are at a disadvantage.
• They are not well-camouflaged in either environment - not dark enough for the trees or light enough for the lichen.

Selection Pressures

• Birds and other predators are less likely to spot and eat moths that closely match the background, either dark or light.

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Disruptive Selection

Result of Disruptive Selection

• Over time, disruptive selection can lead to the development of two distinct phenotypic forms within the moth population.
• High melanin and low melanin moths may become specialised for their respective environments.