Over the years of their existence in the poisoned waters of the Hudson, the perch-like tomcod fish have learned to ignore neurotoxic poisons. So much the worse for their enemies: having accumulated biphenyls, fish oil becomes a very harmful dish
Industrial progress with the ensuing man-made disasters and environmental pollution can be treated in different ways. "Greens" prefer to sound the alarm at every opportunity and celebrate memorial services for already extinct species. Ecologists, with a composure worthy of Buddhism, describe the changes in climatic niches and the opened migration routes for animals. As for evolutionary biologists, it is generally difficult for them to think of more interesting decades than the late 20th and early 21st centuries. After all, right before their eyes, processes are taking place that could have taken hundreds and thousands of years before. The point is not at all a high radiation background, provoking mutagenesis: it is just that in the entire history of the planet, the animal and plant world has not often encountered the rapid emergence of new ecological niches.
A team of scientists led by Mark Hahn of the legendary Woods Hole Oceanographic Institute discovered that pollution of rivers with polychlorinated biphenyls half a century ago led to the emergence of fish in the Hudson, resistant to these super-toxic compounds.
Heat resistance, dielectric properties and low cost of PCBs at one time unconditionally determined the choice of the base and additives for insulators, paints, mastics, lubricants and other components of electrical engineering. The same physicochemical properties make PCBs a powerful poison - they are carcinogenic, accumulate in adipose tissue and belong to the group of neurotoxins, resembling dioxin in their mechanism of action.
PCBs bind to the transcription factor AHR, which controls the functioning of other genes that play a key role in the development of the body, cellular respiration, and hormone synthesis and transport.
In tomcodes resistant to biphenyls, the aforementioned AHR protein is modified - it lacks 2 out of 1104 amino acids.
As a result, it binds more weakly to PCBs, which minimizes toxic effects. Moreover, mutations do not interfere with the performance of their main functions: tomcodes feel great both in nature and in captivity.
To the delight of the authors of the publication in Science, this is the first example of a rapid "mutation of resistance" in vertebrates. Usually fast-dividing bacteria and fungi are more prone to this, only the role of a selection factor is not chemical pollution, but another antibiotic.
The mutated individual gets an undeniable advantage and quickly fills an ecological niche.
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Usually, these genetic changes appear during sexual reproduction (during the formation of gametes), some of them have no effect on the work of the protein, some lead to the appearance of abnormalities that are incompatible with life, and some, as in this case, allow their hosts to reproduce in completely unsuitable conditions for this.
Moreover, resistance to chemistry is also combined with the ability to control the number of predators, because PCBs are stored in the adipose tissue of fish, so that a predator that eats them (including humans) inevitably receives a decent dose of poison.
Despite the absence of visible differences, the “mutants” are still outperformed by the main population of Microgadus tomcod. In less polluted rivers that flow into the Atlantic Ocean north of the Hudson, the main population continues to dominate. Although it was in this region from 1946 to 1970 that General Electric plants emitted 600 thousand tons of biphenyl. The authors suggest that this may be due to increased sensitivity to other contaminants, in particular to polyaromatic hydrocarbons.
Perhaps we just need to wait another half century, and we will see mutant fish, ready to meet any chemistry. The main thing is not to pour too much naphthalene into the river.
