How has pollution influenced the development of melanistic (dark-colored) insects in certain areas?

Sourav PanNovember 8, 2024

Answered

Pollution has significantly influenced the development of melanistic (dark-colored) insects, particularly through a phenomenon known as industrial melanism. This evolutionary response is primarily observed in species like the peppered moth (Biston betularia), which illustrates how environmental changes due to human activities can lead to shifts in coloration and adaptations in insect populations.

Mechanisms of Melanism Development

1. Environmental Changes:
   • Industrial activities, particularly during the 19th and 20th centuries, led to increased air pollution from soot and other pollutants. This pollution darkened surfaces such as tree bark, which previously had light-colored lichens that provided camouflage for lighter moths. As a result, light-colored moths became more visible to predators in polluted areas, leading to a decline in their population.
2. Natural Selection:
   • In contrast, darker (melanic) forms of these insects were better camouflaged against the soot-covered backgrounds, providing them with a survival advantage. This selective pressure favored the melanic variants, leading to an increase in their frequency within the population. The classic example is the peppered moth, where the dark form (F. carbonaria) became predominant in industrial regions due to this selective advantage .
3. Genetic Basis:
   • Research has identified specific genetic mechanisms underlying this melanism. Studies have shown that similar genes are involved in the development of dark coloration across different moth species affected by industrial pollution. For instance, mutations associated with melanism have been linked to the same genetic region (containing the cortex gene) in multiple species, suggesting a convergent evolutionary response to similar environmental pressures .
4. Broader Implications:
   • Melanism is not limited to moths; it has been observed in various insect species and even other animals exposed to pollution. The phenomenon highlights how human-induced environmental changes can drive rapid evolutionary adaptations, demonstrating that species can respond dynamically to anthropogenic pressures .

Additional Factors Influencing Melanism

• Thermal Advantages: Darker coloration can also provide thermal benefits by absorbing more heat from sunlight, which may be advantageous in cooler environments or during periods of low sunlight due to pollution-related haze .
• Immune Function: Some studies suggest that melanic insects may exhibit enhanced immune responses, as melanin plays a role in immune defense mechanisms. This could further support the survival of darker morphs in polluted environments where stressors are elevated .