The rise and fall of the black moth in England

Manchester had many coal-fired factories that released a lot of soot into the air. During this period, reports began to appear about the appearance of a new phenotype (external expression of a trait) for a known species of moth (Biston Betularia or Peppered moths)

the industrial Revolution of the 19th century brought with it technological development and considerable social and economic changes, but also one of the classic examples of natural selection recorded by man. An article published in Science magazine last April adds another line to one of the most famous stories in biology.

The beginning of the story in the middle of the 19th century in the area of ​​the city of Manchester in England. Manchester had many coal-fired factories that released a lot of soot into the air. During this period, reports of the appearance of phenotype (external expression of a feature) new to a known species of moth (Biston Betularia or Peppered moths). Until that time this moth was known as a light gray color with black dots, but now black colored moths have started to appear. By the end of the 19th century, most moths displayed the black phenotype (between 95-98% of the population).

Evolution is defined as a change in frequency the alleles (different forms of expression of the same gene) in the population. A process that causes a change in the inherited characteristics of a population over many generations. This process has two main mechanisms: a. natural selection - a process according to which the individuals with the traits more adapted to the environment are more likely to survive and reproduce. B.genetic drift - Change in the frequency of alleles in the population over time as a result of accidental factors such as natural disasters for example.

The color of the moth in this case is determined by two alleles, gray and black. The black allele is dominant (dominant) and the gray allele is recessive (dominant). Each individual has two alleles of the gene for wing color, and according to this law, in order for an individual to be gray, both of its alleles must be of the gray color. An individual with two alleles for black color or an allele for black color and an allele for gray color will have a black phenotype. The fact that the black allele is dominant explains its rapid takeover of the population. But why didn't this takeover happen earlier?

In 1896 J.W. first proposed Tut (JW Tutt) that natural selection in moths occurred as a result of predation pressures from birds. Until the industrial revolution the tree trunks in the Manchester area were covered inlichens clarity. These lichens enabled a successful camouflage for the gray moths, but black moths were very visible to hungry birds and therefore the amount of black moths was extremely low. When soot from the factories was dispersed in the air, those lichens disappeared since they are sensitive to air pollution. In fact, to this day lichens constitute Bioindicator Good for air pollution. In England the result was dark tree trunks. Now, a gray moth that stops to rest on a tree trunk will stand out well to the eyes of a hungry bird while the black one will be well camouflaged. The change was so noticeable that the frequency of black moths increased from about 2% of the population in 1848 to about 95% of the population in 1895 (and even 98% in certain areas).

Despite many studies done on these moths over the years the molecular level of the change remains a mystery. Although they were able to determine that it is a dominant allele, located on an autosomal chromosome (which does not determine the species of the creature), knowledge is still lacking about the specific change, the mutation, that led to the color change.

On April 14, 2011, researchers from the University of Liverpool in England reported  in Science magazine Because they were able to locate the change to a specific region known to be responsible for creating color patterns on the wings of butterflies and other related species. This region of the genome of moths and butterflies is a "hot spot" for genetic changes where mutations produce hundreds of different color patterns in the wings of many species, including changes related to mimicry from edible species to inedible species and mutations that control the size of the "eyes" on the wings of butterflies designed to scare off potential predators .

After the researchers compared moths collected from 80 sites in Great Britain, they were able to determine with the help of genetic markers that it was a mutation involving a single point in the genome, and not a combination of several points. The researchers also determined that the mutation occurred only once in Britain and not several times.

The emphasis on the fact that the researchers found answers only for the change in Britain is because the change in the frequency of alleles in the moth population occurred at the same time in both continental Europe and the eastern United States in closely related species of moths. More research is needed to determine whether these are identical mutations that occurred at the same time and took over the population as a result of identical environmental pressures, or whether these are different mutations that led to the same phenotype.

Beginning in the 60s, after an increase in awareness of the dangers of air pollution and the improvement of air quality in Great Britain, the lichens returned to the trees and with them the frequency of the gray phenotype increased. Today the black phenotype makes up only a few percent of the moth population.

A point to think about: in order to fulfill the ambition of every biology student and to publish in Science, you don't need innovative and ground-breaking research, it is enough to add a line, not particularly exciting, to one of the great stories of science.