Atlantic killifish able to adapt to high levels of pollution

A comparison of a normally developed Atlantic killifish embryo (Pic 1) and a PCB-affected embryo (Pic 2): The fish has a deformed heart. Killifish that have evolved tolerance to chemical exposure show limited signs of developmental defects. (c) Bryan Clark/U.S. EPA

Wild Atlantic killifish populations have been found to possess the ability to adapt to toxic pollution, according to a new report published in the Science journal. A collaborative team of researchers from several institutions have discovered that some populations of this fish living in urban estuaries are up to 8,000 times more resistant than others to highly toxic industrial pollutants like dioxins, heavy metals and hydrocarbons. To identify the mechanism behind the adaptation, the genomes of four wild populations of pollution-tolerant killifish were compared with four non-tolerant populations. The genes responsible for the trait were found to be those involved in the aryl hydrocarbon receptor (AHR) signalling pathway, which combined with observations of desensitisation of this pathway in tolerant populations, led the researchers to conclude that the AHR pathway was a key target of natural selection. According to a press release issued by the University of Birmingham: " 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. Professor John Colbourne, the University's Chair of Environmental Genomics oversaw the sequencing of the genomes. He said that the report highlighted the complexity of the processes involved in the fish's adaptation, saying that the Atlantic killifish was well-positioned to evolve the necessary adaptations due to their large population sizes and relatively high level of DNA diversity in their populations. He added, " 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. Despite their findings, the research team cautions against using their discovery to justify polluting the natural environment. Lead author Andrew Whitehead, associate professor in the University of California Davis' Department of Environmental Toxicology 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. " Read more: The genomic landscape of rapid repeated evolutionary adaptation to toxic pollution in wild fish

A comparison of a normally developed Atlantic killifish embryo (Pic 1) and a PCB-affected embryo (Pic 2): The fish has a deformed heart. Killifish that have evolved tolerance to chemical exposure show limited signs of developmental defects. (c) Bryan Clark/U.S. EPA

Atlantic killifish like this one have evolved to adapt to highly toxic levels of pollution. (c) Andrew Whitehead/UC Davis