How otters' muscles enable their cold, aquatic life

Date:
July 9, 2021
Source:
Texas A&M University
Summary:
Sea otters are the smallest marine mammal. As cold-water dwellers,
staying warm is a top priority, but their dense fur only goes so
far. We have long known that high metabolism generates the heat
they need to survive, but we didn't know how they were producing
the heat -- until now.



FULL STORY ==========================================================================
Sea otters are the smallest marine mammal. As cold-water dwellers, staying
warm is a top priority, but their dense fur only goes so far. We have
long known that high metabolism generates the heat they need to survive,
but we didn't know how they were producing the heat -- until now.


========================================================================== Researchers recently discovered that sea otters' muscles use enough
energy through leak respiration, energy not used to perform tasks, that
it accounts for their high metabolic rate. The finding explains how sea
otters survive in cold water.

Physiologist Tray Wright, research assistant professor in Texas A&M University's College of Education & Human Development, conducted the
study along with colleagues Melinda Sheffield-Moore, an expert on human skeletal muscle metabolism, Randall Davis and Heidi Pearson, marine
mammal ecology experts, and Michael Murray, veterinarian at the Monterey
Bay Aquarium. Their findings were published in the journal Science.

The team collected skeletal muscle samples from both northern and southern
sea otters of varying ages and body masses. They measured respiratory
capacity, the rate at which the muscle can use oxygen, finding that the
energy produced by muscle is good for more than just movement.

"You mostly think of muscle as doing work to move the body," Wright
said. "When muscles are active, the energy they use for movement also
generates heat." Wright said that because muscle makes up a large
portion of body mass, often 40-50% in mammals, it can warm the body up
quickly when it is active.



========================================================================== "Muscles can also generate heat without doing work to move by using a
metabolic short circuit known as leak respiration," Wright said.

A form of muscle-generated heat we are more familiar with is
shivering. Wright said this involuntary movement allows the body to
activate muscle by contracting to generate heat, while leak respiration
can do the same without the tremors.

Wright said one of the most surprising findings was that the muscle of
even newborn sea otters had a metabolic rate that was just as high as
the adults.

"This really highlights how heat production seems to be the driving
factor in determining the metabolic ability of muscle in these animals,"
Wright said.

Sea otters require a lot of energy to live in cold water. They eat up
to 25% of their body mass per day to keep up with their daily activities
and fuel their high metabolism.



========================================================================== "They eat a lot of seafood, including crabs and clams that are popular
with humans, which can cause conflict with fisheries in some areas,"
Wright said.

Wright said we know how critical muscle is to animals for activities
like hunting, avoiding predators and finding mates, but this research highlights how other functions of muscle are also critical to animal
survival and ecology.

"Regulating tissue metabolism is also an active area of research in the
battle to prevent obesity," Wright said. "These animals may give us clues
into how metabolism can be manipulated in healthy humans and those with diseases where muscle metabolism is affected." As for future research,
Wright said there is still a lot we don't know about otters, including
how they regulate their muscle metabolism to turn up the heat on demand.

"This is really just the first look into the muscle of these animals, and
we don't know if all the various muscle types are the same, or if other
organs might also have an elevated ability to generate heat," Wright said.

========================================================================== Story Source: Materials provided by Texas_A&M_University. Original
written by Heather Janak.

Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Traver Wright, Randall W. Davis, Heidi C. Pearson, Michael Murray,
Melinda Sheffield-Moore. Skeletal muscle thermogenesis enables
aquatic life in the smallest marine mammal. Science, 2021; 373
(6551): 223 DOI: 10.1126/science.abf4557 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/07/210709193517.htm

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