Atlantic killifish like this one have adapted to highly toxic levels of pollution. Credit: Andrew Whitehead/UC Davis
A few species over time have adapted to the harsh realities of environmental pollution. Evolution is working hard to rescue some urban fish from a lethal, human-altered environment, according to a study which was published Dec. 9 in the journal Science and led by the University of California, Davis. Atlantic killifish living in four polluted East Coast estuaries have adapted to levels of highly toxic industrial pollutants that would normally kill them.
Normally, environmental change is believed to outpace the rate of evolution for several other species of plants and animals. However, The Atlantic killifish which live in four polluted East Coast estuaries turn out to be very resilient to the high pollution. These fish have adapted to levels of highly toxic industrial pollutants that would normally kill them.
The killifish is up to 8,000 times more resistant to this level of pollution than other fish, the study found. While the fish is not commercially valuable, it is an important food for other species and an environmental indicator.
This can be accredited to the extremely high levels of genetic variation of this fish species, actually higher than any other vertebrate measured so far (including humans!). The more genetic diversity, the faster evolution can act. This is one reason why insects and weeds can quickly adapt and evolve to resist pesticides, and why pathogens can evolve quickly to resist drugs created to destroy them.
It is easy to believe that this is the same for all other species with high genetic diversity. said lead author Andrew Whitehead, associate professor in the UC Davis Department of Environmental Toxicology. “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.”
The scientists sequenced complete genomes of nearly 400 Atlantic killifish from polluted and non-polluted sites at New Bedford Harbor in Massachusetts; Newark Bay, New Jersey; Connecticut’s Bridgeport area; and Virginia’s Elizabeth River. The sites have been polluted since the 1950s and 1960s by a complex mixture of industrial pollutants including dioxins, heavy metals, hydrocarbons and other chemicals.
The team’s genetic analysis suggests that the Atlantic killifish’s genetic diversity make them unusually well positioned to adapt to survive in radically altered habitats. At the genetic level, the tolerant populations evolved in highly similar ways. This suggests that these fish already carried the genetic variation that allowed them to adapt before the sites were polluted, and that there may be only a few evolutionary solutions to pollution.
The study lays the groundwork for future research that could explore which genes confer tolerance of specific chemicals. Such work could help better explain how genetic differences among humans and other species may contribute to differences in sensitivity to environmental chemicals.
“If we know the kinds of genes that can confer sensitivity in another vertebrate animal like us, perhaps we can understand how different humans, with their own mutations in these important genes, might react to these chemicals,” Whitehead said.
“This study shows that different populations of Atlantic killifish exposed to toxic pollution evolve tolerance to that pollution through changes in one molecular pathway,” said George Gilchrist, program director in the National Science Foundation’s Division of Environmental Biology, which funded the study along with the National Institute of Environmental Health Sciences. “This pathway may play a similar role in many animals exposed to pollutants, with slightly different adaptations in response to different toxicants.”