Humans aren't the only species whose metabolisms tend to slow down with
age

Date:
August 13, 2021
Source:
Duke University
Summary:
If you feel like your metabolism just isn't what it used to be, no
matter how many hours you spend in the gym, dolphins can relate. A
new study finds that bottlenose dolphins burn calories at a lower
rate as they get older, just like we do.



FULL STORY ==========================================================================
If you feel like your metabolism just isn't what it used to be, no matter
how many hours you spend in the gym, dolphins can relate.


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A Duke University-led study finds that bottlenose dolphins burn calories
at a lower rate as they get older, just like we do.

It's the first time scientists have measured an age-related metabolic
slowdown in another large-bodied species besides humans, said first author Rebecca Rimbach, postdoctoral associate in evolutionary anthropology
at Duke.

Rimbach has studied energy expenditure and other aspects of physiology
in animals ranging from mice to monkeys. But data on the inner workings
of marine mammals such as dolphins and whales have been scant, she
says. That's because these ocean dwellers are notoriously difficult to recapture for repeat measurements.

"It can be very tricky to get the animal back when you need it,"
Rimbach said.

The researchers studied 10 bottlenose dolphins aged 10 to 45 living at
two marine mammal facilities, Dolphin Research Center in Florida and
Dolphin Quest in Hawaii.



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To measure their average daily metabolic rate, the researchers used the
"doubly labeled water method." Used to measure energy expenditure in
humans since the 1980s, it's a method that involves getting the animals
to drink a few ounces of water with naturally occurring "heavy" forms
of hydrogen and oxygen added, and then tracking how long the animals
take to flush them out.

Like humans present their arms for a blood draw, the dolphins at these facilities voluntarily raise their tail fins out of the water so their caregivers can collect blood or urine as part of their regular checkups.

By analyzing the levels of heavy hydrogen and oxygen atoms in the blood
or urine, the team was able to calculate how much carbon dioxide the
dolphins produced each day, and thus how many calories they were burning
as they went about their lives.

What they found surprised them.

The researchers expected dolphins to have revved-up metabolisms, since
dolphins are warm-blooded just like people, and keeping warm requires
more energy in water than in air.



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But despite living in a watery world, they found that bottlenose
dolphins burn 17% less energy per day than expected for a marine mammal
of their size.

The scientists also noted some of the same signs of metabolic aging
common in people. The oldest dolphins in the study, both in their 40s,
used 22% to 49% fewer calories each day than expected for their body
weight. And similar to humans, more of those calories ended up as fat
rather than muscle. Dolphins in their 40s had body fat percentages that
were 2.5 times higher than their under- 20 counterparts.

It wasn't for lack of exercise, Rimbach said. Dolphins are amazing
athletes, capable of leaping 10 feet into the air and swimming alongside
power boats at speeds that would crush Michael Phelps.

The dolphins in the study were observed doing flips and spins, walking
on their tails, jumping clear out of the water and going fast enough
to leave a wake as often as six to 18 times an hour, and they remained
active into their 40s.

But the metabolic pattern remained no matter what their activity level.

"And it's not because they're eating too much," either, Rimbach said. The researchers recorded how much herring and other fish the dolphins gobbled
up, and they found that the older, fatter dolphins in the study actually
ate fewer calories.

The researchers say such work could shed light on factors besides diet
and lifestyle that underlie age-related weight gain in people.

"Further studies into this commonality we share with dolphins may help us understand why human metabolism slows as we age," said co-author Hannah Salomons, a graduate student in professor Brian Hare's lab at Duke.

"Having access to healthy dolphins under human care made this study
possible," said co-author Austin Allen of the Duke University Marine Lab.

"We need more data, especially for younger
dolphins, since we only looked at 10 individuals,"
Rimbach said. "But I think it's an exciting first study." ========================================================================== Story Source: Materials provided by Duke_University. Original written
by Robin A. Smith.

Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Rebecca Rimbach, Ahmad Amireh, Austin Allen, Brian Hare, Emily
Guarino,
Chana Kaufman, Hannah Salomons, Herman Pontzer. Total energy
expenditure of bottlenose dolphins (Tursiops truncatus) of
different ages. Journal of Experimental Biology, 2021; 224 (15)
DOI: 10.1242/jeb.242218 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/08/210813100301.htm

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