Survival Of The Sluggish: Scientists Find An Upside To A Low Metabolism

Aug 29, 2018
Originally published on August 29, 2018 9:14 am

New research suggests one effective evolutionary strategy: be lazy.

Species of mollusks that are now extinct had higher metabolic rates than the species that exist today, scientists announced in a paper published this week in Proceedings of the Royal Society B.

Metabolic rates are the amount of energy that organisms need to carry out their daily lives. Luke Strotz, a paleontologist and post-doctoral researcher at the University of Kansas who is lead author of the paper, says that a high basal metabolic rate has already been shown to lead to a higher likelihood of death at the individual level.

"But that that scales up to the level of the species is probably the big finding of this study," he tells NPR. "That you can take something that's happening at the level of all those individuals, scale it up to this level of the species, and see that at the species level higher metabolic rates actually has an influence on the likelihood of that species actually going extinct."

Researchers looked at the metabolic rates of 299 species of mollusks that have lived since the mid-Pliocene era, a span of roughly 5 million years. They specifically analyzed bivalves (clams, mussels) and gastropods (snails, slugs).

How do you figure out the metabolic rate of an extinct scallop? In part by measuring its shell –and there are a lot of mollusk fossils out there, making them ideal for this project.

"Mollusks have extremely long fossil records," says Strotz. "They go back almost to the beginnings of animal life."

He says that previous research has shown that extinction is linked to things like how much area a species occupies, the size of a species' population, or how connected the various populations of a species are to one another.

"We hadn't really pinned down that there was a physiological component to the likelihood of extinction of a species" until this paper, Strotz says — though he cautions the results only consider mollusks.

He says he hopes to expand the team's research to other types of animals, including vertebrates. Until then, alas, we can't draw conclusions about the survival of certain couch-dwelling organisms.

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All right, let me give you a big reason to listen to this next story about a clam's metabolism - because the essential conclusion is it is better to be lazy. Here's NPR's Laura Wamsley.

LAUREL WAMSLEY, BYLINE: Luke Strotz is a paleontologist at the University of Kansas who studies extinctions. But he's not so interested in big asteroids slamming into Earth. He studies small physical differences between animals that go extinct and ones that survive. And the thing that he's really hung up on is how animals use energy, their metabolism.

LUKE STROTZ: Can we look at the metabolism of an organism and say something about the likelihood of that particular species going extinct?

WAMSLEY: He and his colleagues decided to study 5 million years of mollusks.

STROTZ: Specifically, I was looking at what are called bivalves and gastropods, which essentially are clams and snails. They go back almost to the beginnings of animal life.

WAMSLEY: Checking the metabolic rates of living clams was pretty easy. The researchers can watch their vital signs, like respiration.

STROTZ: But you can't do that for a fossil organism, obviously, because they're dead. They're not respiring anymore.

WAMSLEY: So instead, they measured their shells and used climate models to estimate the metabolic rates. The results...

STROTZ: We find that the species that have gone extinct have higher metabolic rates than the species that are still currently living.

WAMSLEY: Yep, it's survival of the sluggish. On the individual level, a higher metabolism is correlated with higher rates of mortality and cell decay.

STROTZ: That that scales up to the level of the species is probably the big finding of this study.

WAMSLEY: And it means that metabolic rate could potentially be used to predict future extinction patterns. But, he cautions, the results only apply to mollusks. So we'll have to wait for more research to see if this finding applies to vertebrates and certain couch-dwelling organisms.

Laurel Wamsley, NPR News.

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