Pollution-proof fish borrow genes from relatives to survive toxins


The Atlantic killifish helped its relative evolve

Andrew Whitehead

In comic books, falling into a vat of toxic chemicals can give you super powers. The same is sort of true for one species of fish – with help from a superhero relative.

The 15-centimetre-long Gulf killifish (Fundulus grandis) lives in estuaries around the Gulf of Mexico, some of which are heavily polluted. They survive levels of toxic halogenated and polycyclic aromatic hydrocarbons (HAHs and PAHs) that cause lethal deformities in other animals. The killifish in these regions have evolved resistance in less than 60 years.

To discover how they did it, Elias Oziolor of Baylor University in Texas and colleagues compared the genomes of the toughest fish with those from less polluted areas. They found that many of the genetic variants conferring resistance come from a related species, the Atlantic killifish or mummichog (Fundus heteroclitus) – an astonishingly tough fish that has evolved resistance to many pollutants.

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That’s surprising because the mummichog normally lives along the Atlantic coast, and the nearest population to the Gulf of Mexico is 2500 kilometres away in Florida. The team think a few mummichog were carried to the Houston Ship Channel, possibly in the ballast water of ships, where they mated with Gulf killifish.

It is now clear that evolution can happen extremely rapidly. However, it requires lots of genetic variation for natural selection to act on. It appears the Gulf killifish did not harbour enough variation among themselves but were saved by genes introduced by hybridisation.

Because many threatened species have lost genetic diversity just when they need it to adapt to a changing world, some biologists have suggested that we should deliberately hybridise species to provide more diversity for evolution to act on.

This is controversial because hybridisation can also lead to a loss of diversity. For instance, in places like the African lakes once separate species are merging together as they hybridise.

“Despite its potential to contribute to diversity, hybridisation carries risks and can even threaten species with extinction,” writes Karin Pfennig of the University of North Carolina in an article accompanying the research. “To guide conservation efforts, scientists need to clarify the conditions under which hybridisation diminishes rather than enhances biodiversity in a rapidly changing world.”

Journal reference: Science, DOI: 10.1126/science.aav4155

 

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