Toxic triumph: fish species in polluted waters steals genes from another

Research reveals rapid hybridisation and a population rebound. Stephen Fleischfresser reports.

The Gulf Killifish, fighting back against pollutants by stealing genes from a relative.


While humans pollute the natural world at an unprecedented rate, some organisms are rapidly adapting to their now toxic environments by borrowing DNA from other species and turning themselves into novel and resilient hybrids, new research shows.

Since Charles Darwin first published On the Origin of Species, adaptive evolution has been thought of as a slow and gradual process. In 1972, the palaeontologists Niles Eldredge and Stephen Jay Gould rocked the boat by suggesting instead that evolution could take large and rapid jumps, via their theory of punctuated equilibrium.

Now a new paper published in the journal Science adds to the growing recognition that evolution can sometimes defy our expectations and move at a pace undreamt of by Darwin.

It also holds out some hope for species affected by human-generated change in environments and climate, changes driving a new mass extinction event to rival the big five.

For 60 years, humans have been carelessly polluting the waters of the Gulf of Mexico via shipping and environmental calamities such as the Deepwater Horizon oil spill. Consequently, the environment has enormously high levels of various hydrocarbons which can have a dreadful effect on wildlife.

The Gulf killifish (Fundulus grandis), an organism that has the deep misfortune to live in the Houston Ship Channel, one of the busiest port entrances in the US, was almost wiped out by pollution.

A toxin called halogenated aromatic hydrocarbons (HAHs), found in abundance in the Channel, causes fatal deformities in the hearts of newborn killifish. As a result, the population went into steep decline.

However, lead author Elias Oziolor and colleagues, mostly from Baylor University in Texas and the University of California, Davis, have discovered that the killifish is recovering. Surprisingly, the fish have suddenly become resistant to the deformity-causing toxins.

So how did this happen? Ironically, just as human carelessness caused the problem in the first place, it might also have provided the solution.

Some 2500 kilometres away lives the Atlantic killifish (Fundulus heteroclitus). This little species, write the authors, “has also adapted to similar chemicals”.

Through another moment of human thoughtlessness, the Atlantic killifish seem to have been accidentally deposited in the Gulf of Mexico through the emptying of ship ballast.

Once there, the introduced species appears to have had a limited level of interbreeding with the local Gulf killifish population, and in the process created hybrids possessing the Atlantic killifish’s genes for resistance to HAHs.

The hybrid, and the injection of new genetic material, has enabled a remarkably rapid adaptation to the changed environment – and led to the revival of the species.

However, Karin S Pfennig from the University of North Carolina, in a companion Perspective piece in the same issue of the journal, notes that interspecies mating can be a double-edged sword.

“Hybridisation,” she writes, “can also be an evolutionary dead end and a threat to diversity; it can reduce population fitness and cause species to collapse.”

The science is unclear at the moment. It is hard to predict which way things will go in a given situation. “Ultimately we still need to clarify the conditions under which hybridisation diminishes versus enhances biodiversity in a rapidly changing world,” she writes.

Nonetheless, Oziolor and colleagues remain optimistic, writing that “our work shows that hybridisation can provide variation crucial for adaptation following swift and extreme environmental change”.

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Stephen fleischfresser.jpg?ixlib=rails 2.1
Stephen Fleischfresser is a lecturer at the University of Melbourne's Trinity College and holds a PhD in the History and Philosophy of Science.
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