An Evolutionary Rescue in Polluted Waters

Atlantic Killifish

The researchers sequenced the genomes of hundreds of Gulf killifish living across a spectrum of toxicity - from clean water, moderately polluted water and very polluted water. They were searching for the footprints of natural selection that allowed the species to rapidly transition from a fish that is highly sensitive to pollution to one extremely resistant to it.

They were surprised to find that the adaptive DNA that rescued this Gulf Coast species came from an Atlantic Coast species of killifish, which has also been known to rapidly evolve high levels of pollution resistance. But Atlantic Coast killifish live at least 1,500 miles from their Houston brethren, leaving researchers to think their transport to the Gulf was likely an accident initiated by humans.

Nonnative species can wreak environmental havoc on native species and habitats. But in this case, their arrival in the 1970s--right at a moment when Gulf killifish were likely beginning to decline--amounted to an "evolutionary rescue" from pollution for the Gulf killifish.

"While the vast majority of research on invasive species rightly focuses on the environmental damage they can cause, this research shows that under rare circumstances they can also contribute valuable genetic variation to a closely related native species, thus acting as a mechanism of evolutionary rescue," said co-corresponding author Cole Matson, an associate professor at Baylor University.