Marine mammals such as dolphins, manatees, seals and whales, which evolved to make water their primary habitat, lost the ability to make a gene that defends humans and other land-dwelling mammals from the neurotoxic effects of a popular human-made pesticide, a new study has revealed.
The researchers found that the marine mammals lost the gene Paraoxonase 1 (PON1) that effectively defends humans and other terrestrial mammals from organophosphates — a group of man-made insecticides.
PON1 potentially reduces cellular damage caused by unstable oxygen atoms and also protects us from organophosphates that kills by disrupting neurological systems.
Whales and dolphins lost the gene PON1 soon after they split from their common ancestor with hippopotamuses 53 million years ago; manatees lost it after their split from their common ancestor with elephants 64 million years ago.
But some seals likely lost PON1 function more recently, at most 21 million years ago and possibly in very recent times.
“The big question is, why did they lose function at PON1 in the first place? It’s hard to tell whether it was no longer necessary or whether it was preventing them from adapting to a marine environment,” said lead author Wynn K. Meyer, postdoctoral associate at the University of Pittsburgh in the US.
“We know that ancient marine environments didn’t have organophosphate pesticides, so we think the loss might instead be related to PON1’s role in responding to the extreme oxidative stress generated by long periods of diving and rapid resurfacing,” Meyer added.
For the study, appearing in the journal Science, the team analysed DNA sequences from five species of marine mammals and 53 species of terrestrial mammals and reacted their blood samples with an organophosphate by-product.
The blood did not break down the organophosphate by-product the way it did in land mammals, indicating that unless a different biological mechanism is protecting the marine mammals, they would be susceptible to organophosphate poisoning — a form of poisoning that results from the build-up of chemical signals in the body, especially the brain.