“Sentinel Species of the 6th Mass Extinction” –Marine Mammals May Not Survive the Anthropocene



“Marine mammals, such as manatees or bottlenose dolphins, are sentinel species—the canary in the coal mine,” says Nathan Clark,  associate professor in Pitt’s Department of Computational and Systems Biology, and the Pittsburgh Center for Evolutionary Biology and Medicine. “If you follow their health, it will tell you a lot about potential environmental issues that could eventually affect humans.”

When a group of small, hoofed mammals slid into Earth’s blue estuaries during the Eocene Epoch, they gradually evolved into today’s whales and dolphins becoming color-blind and losing their sense of smell and taste. And they also lost critical gene called PON1 that makes them vulnerable to ocean-born pesticides, says Clark.

But they also face, along with human species, a far greater threat, says Clark.

Our blue planet is in the grips of the Sixth Mass Extinction: the best-case scenario projects that humans will add 300 gigatons of carbon to the oceans by 2100, while more than 500 gigatons will be added under the worst-case scenario, far exceeding the critical threshold, according to Daniel Rothman professor of geophysics and co-director of MIT’s Lorenz Center. By 2100, the carbon cycle will either be close to or well beyond Earth’s threshold for catastrophe.

“The predictions Daniel Rothman makes would have grave consequences for most of life on Earth,” Clark said in an email to dailygalaxy.com. “The rapid warming would cause major environmental changes that smaller, more fragile populations of species may not be able to keep up with adapting. In addition to the loss of land area by rising ocean levels, marine ecosystems could also change, such as through the shifting or halting of major ocean currents. Current changes would have major impacts on food sources for whales and other marine predators. These major ecosystem changes would be a much larger concern than the loss of the PON1 gene.”

In an attempt to learn why marine mammals lost PON1 function, the researchers traced back when the function was lost in three different groups of marine mammals, writes Ed Yong in The Atlantic. “Whales and dolphins lost it 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?” said lead author Wynn K. Meyer. “It’s hard to tell whether it was no longer necessary or whether it was preventing them from adapting to a marine environment. 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. 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.”

“One of the key messages that comes out very strongly from the recent UN Intergovernmental Panel on Climate Change (IPCC) report is that we are already seeing the consequences of 1°C of global warming through more extreme weather, rising sea levels and diminishing Arctic sea ice, destruction of ancient coral reefs, among other changes,” said Panmao Zhai, Co-Chair of IPCC Working Group I.

“How can you really compare these great events in the geologic past, which occur over such vast timescales, to what’s going on today, which is centuries at the longest?” asks Rothman.

Dinosaurs may have ruled the land 66 million years ago during the Cretaceous period but the oceans belonged to the ammonites. But volcanic activity and climate change already placed ammonites under stress. The asteroid impact that ended the dinosaurs’ reign provided the final blow. Only a few dwindling species of ammonites survived. Today, the ammonites’ oldest surviving relative is the nautilus. Will it survive the sixth great extinction? Will the whales and marine mammals? Will the human species?

The Daily Galaxy via University of Pittsburgh Schools of the Health Sciences, MIT, PLOS 1, and The Atlantic

Image credit top of page: With thanks to anipedia.net

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