Texas A&M researchers found that thermogenic leaks from their skeletal muscles heat the small mammals internally, which increases their metabolic rate
Photo credit: Tray Wright / Texas A&M University (Image obtained from R. Davis under USFWS Marine Mammal Permit No.MA-043219)
Sea otters are the smallest marine mammals. As cold-water residents, staying warm is a top priority, but their thick fur only goes so far. We’ve long known that high metabolism creates the heat they need to survive, but we didn’t know how they produce the heat – until now.
Researchers recently found that sea otters’ muscles use enough energy through leaky breathing, energy not used to perform tasks, and that this is responsible for their high metabolism. The find explains how sea otters survive in cold water.
Physiologist Tray Wright, research assistant at Texas A&M University’s College of Education & Human Development, led the study with colleagues Melinda Sheffield-Moore, an expert in human skeletal muscle metabolism, Randall Davis and Heidi Pearson, experts in marine mammal ecology, and Michael by Murray, veterinarian at the Monterey Bay Aquarium. Their results were published in the journal science.
The team collected skeletal muscle samples from northern and southern sea otters of different ages and body masses. They measured breathing capacity, the rate at which the muscle could use oxygen, and found that the energy the muscle produced was good for more than just movement.
“Most of the time, you think of muscles as work to move the body,” Wright said. “When the muscles are active, the energy they use for movement also generates heat.”
Wright said that since muscles make up a large chunk of body mass, often 40-50% in mammals, they can quickly warm the body up when it’s active.
“Muscles can also generate heat without doing any work to move using a metabolic short circuit known as leaky breath,” Wright said.
One form of muscle-generated heat that we are more familiar with is tremors. Wright said that this involuntary movement allows the body to activate the muscles by contracting to create heat, while leaky breathing can do the same without tremors.
Wright said one of the most surprising discoveries was that the muscle of even newborn sea otters had as high a metabolic rate as that of adults.
“This really highlights how heat production appears to be the driving factor in determining the metabolic ability of the muscles 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 to get their high metabolism going.
“They eat a lot of seafood, including crabs and clams, which are popular with humans, which in some areas can conflict with fisheries,” Wright said.
Wright said we know the importance of muscles to animals in activities like hunting, predator avoidance, and dating, but this research shows that other muscle functions are also critical to animal survival and ecology.
“The regulation of tissue metabolism is also an active area of research in the fight against obesity,” said Wright. “These animals can give us clues as to how the metabolism can be manipulated in healthy people and those with diseases in which the muscle metabolism is affected.”
As for future research, Wright says there is still a lot we don’t know about otters, including how they regulate their muscle metabolism to increase heat when needed.
“This is really just the first look inside the muscles of these animals, and we don’t know if all the different types of muscles are the same or if other organs also have an increased ability to generate heat,” Wright said.