As marine mammals evolved, they lost the ability to make a protein that defends their land-dwelling counterparts from the neurotoxic effects of popular pesticides known as organophosphates.
The implications of this finding, uncovered by scientists at the University of Pittsburgh School of Medicine and published in the journal Science, have led to calls for greater monitoring of waterways and agricultural runoff.
Researchers already know that some of the genes responsible for the senses of smell and taste in terrestrial animals lost their function during the evolution of marine mammals. The authors of the new study set out to discover what other genes preserved in land-dwelling mammals had lost function in marine mammals, such as dolphins, manatees and whales.
They determined that the gene Paraoxonase 1 (PON1) – which encodes an enzyme that protects humans and other terrestrial mammals from insect-killing organophosphates – had been shut down in most marine mammals.
As a result, these creatures may be susceptible to a form of neurological poisoning that stems from chemical build-up in the brain. The researchers traced the loss of PON1 function in dolphins and whales back to the time of their split from their common ancestor with the hippopotamus – around 53 million years ago.
Manatees lost PON1 function around 64 million years ago, while seals lost it 21 million years ago. It’s not yet known what environmental factors prompted the shift, though there are a number of possibilities.
“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,” explains Wynn K. Meyer, the study’s lead author.
The next step in this research is to launch an additional study that observes marine mammals during and shortly after periods of excess agricultural organophosphate runoff.
“If we can figure out why these species don't have functional PON1, we might learn more about the function of PON1 in human health, while also uncovering potential clues to help protect marine mammals most at risk," Meyer says.