Industrial Melanism

Abstract

Industrial melanism refers to the evolution of dark body colours in animal species that live in habitats blackened by industrial soot. The phenomenon has been documented in numerous species that hide from predators by blending in with their backgrounds. Peppered moths provide one example. Before the industrial revolution, peppered moths in the UK were pale grey, but after their habitats became polluted with soot from coal‐fired industries, melanic (black) phenotypes became numerous and spread to other regions. Away from industrial centres, the pale phenotype remained common. Following clean air legislation a century later, the atmosphere improved, soot‐damaged habitats gradually recovered, and the pale phenotype returned as the predominant form. Parallel changes have occurred in America. The melanic and pale phenotypes are determined by genes, and the changes in their percentages in populations reflect natural selection. Experiments identify bird predation on the moth phenotypes as the agent of selection. Key Concepts: The natural colour patterns of animals are adaptations produced by natural selection. A change in frequency (percentage) of genetically determined phenotypes in natural populations is direct evidence of evolutionary change. Mutations introduce new genetic variation to a population, but recurrent mutations occur too rarely to bring about rapid changes in the frequency of genes. Random changes in the frequency of genes (genetic drift) are irregular and unpredictable in direction. Directional, rapid changes in the frequency of genetically determined phenotypes in populations result from natural selection. Historical records on phenotypic frequencies from population samples allow the assessment of natural selection. Gene flow (migration) retards genetic differentiation among geographically widespread populations. Clines indicate different selection pressures along environmental gradients; when selection is removed, migration homogenises the differences along a cline. Parallel evolution is ‘nature's replicate experiment’.

Towards an ecology of protective coloration

“…(3) Colour polymorphisms and colour change Colour polymorphisms (Table 1) Ecology of protective coloration result from predation pressure: background matching against different microhabitats, as responses to spatio-temporal variation in ecological conditions, or frequency-dependent selection resulting from predator search-image formation (see Nokelainen et al, 2012;Rojas & Endler, 2013;McLean & Stuart-Fox, 2014;Price et al, 2019). Venerated examples of colour polymorphisms that involve background matching to different microhabitats are the normal and melanistic forms of the peppered moth Biston betularia (Grant, 2012) and the pelage colour of oldfield mice Peromyscus polionotus (Belk & Smith, 1996). A more recent example comes from the marine shrimp Hippolyte obliquimanus that has a homogeneous morph of variable colours and a transparent morph with coloured stripes.…”

Camouflage

“…Writing some 15 years before his grandson Charles was even born, Erasmus Darwin was using animal camouflage to illustrate apparent design in nature. Over two centuries later, the peppered moth Biston betularia remains the textbook example of rapid evolution, driven by changes in the effectiveness of camouflage against altered backgrounds (Grant, ; Cook & Saccher, ). However, recent years have seen a change in the focus of research on camouflage, towards a dissection of the multiple mechanisms at play.…”

Stable laws in a changing world The structure of evolutionary theories over the centuries

“…In the genomic era, haplotypes, i.e., the set of alleles located closely on a single chromosome and tend to be passed to the offspring together, are also investigated as reproductive units besides genes. Selective sweeps of the carbonaria haplotype of Biston betularia in Britain (Grant 2012) and the lactase persistence haplotypes in several human populations (Tishkoff et al 2007) are well-known examples.…”