How some fish survive toxic pollution levels decoded

Atlantic killifish may be up to 8,000 times more resistant to highly toxic industrial pollutants such as heavy metals due to the high level of DNA diversity seen in their populations, a new study has found.
The Atlantic killifish is renowned for its ability to tolerate large fluctuations in temperature, salinity and oxygen levels.
However, its rapid adaptation to the normally lethal levels of toxic pollution found in some urban estuaries in the US is unusual, even for such a hardy species.
Researchers including those from the University of Birmingham in the UK, analysed the genomes of four wild populations of pollution-tolerant killifish compared with four non-tolerant populations, to identify the mechanism behind this adaptation.

They found that the genes responsible for the trait were those involved in the aryl hydrocarbon receptor (AHR) signalling pathway, which combined with observations of desensitisation of this pathway in tolerant populations, led them to conclude that the AHR pathway is a key target of natural selection.
The team also showed that the potentially negative effects of desensitisation of the AHR pathway were ameliorated through compensatory adaptations in terms of cell cycle regulation and immune system function.

This, combined with the diversity of pollutants present in estuaries, results in a relatively complex adaptive genotype in wild populations compared to that of laboratory models.

"This report highlights the complexity of the processes involved in the adaptation of wild fish to lethal levels of environmental pollution," said John Colbourne, Chair of Environmental Genomics at the University of Birmingham.
"It also demonstrates how the DNA of populations that differ in their susceptibility to pollutants can reveal "signatures" of the adverse effects of chemicals in the environment," Colbourne said.
"The Atlantic killifish seem particularly well-positioned to evolve the necessary adaptations to survive in radically altered habitats, because of their large population sizes and the relatively high level of DNA diversity seen in their populations," he said.
The researchers warn that these findings should not be used to justify the harm caused by human pollution of the natural environment.

Department of Environmental Toxicology and lead author on the study, said:
"Unfortunately, most species we care about preserving probably can't adapt to these rapid changes because they don't have the high levels of genetic variation that allow them to evolve quickly," said Andrew Whitehead, associate professor at University of California, Davis in the US.
The study was published in the journal Science.