It cannot be the fur alone and the smallest marine mammals in the world do not have an insulating layer of fat either. Researchers have now clarified how sea otters can withstand the low water temperatures in the North Pacific. The power plants in the animals’ muscle cells therefore release heat energy particularly intensively even when they are at rest and without trembling. The price for internal heating, however, is an enormous need for food.
She is famous for her cute looks and the use of stones to open shellfish. Sea otters (Enhydra lutris) is also characterized by a record: At up to around 40 kilograms, they are the smallest of all marine mammals. The special thing is that this low body mass can hardly protect you from the low water temperatures. In contrast to sea lions and Co, they also do not have an insulating layer of fat. Instead, they have developed an extremely dense fur, but this cannot explain how they can keep warm in the water in their habitat, which is often only just above zero degrees Celsius. Apparently sea otters have to keep their body temperature stable through a high metabolism. How they generate their inner warmth, however, was previously unknown.
Motionless muscle heating
The researchers around Tray Wright from Texas A&M University in College Station investigated this question. They focused on the animals’ muscles. Because in mammals this tissue makes up a large part of the body mass and, as is well known, it can provide rapid warming through activity. As part of the study, the scientists examined samples of muscle tissue that came from sea otters of different ages and weights. Using respirometry methods, they analyzed the rate at which the muscle tissue consumes oxygen. Comparisons with values in other animal species then made it possible to draw conclusions about peculiarities in the characteristics of the sea otter muscles, the researchers explain.
As they report, their results show that the so-called leak respiration in the muscles of sea otters is particularly intensive in releasing heat. It is a metabolic process in the power plants of the cells (mitochondria), in which no energy carriers are generated for movement, but heat energy is released nonetheless. The involuntary muscle movement that causes us to develop heat when we are hypothermic is therefore not necessary – the tremor. Heat generation through leakage breathing was already known from other animal species. But the sea otters achieve top values, according to the studies: The process accounts for up to 40 percent of the total respiratory capacity in the muscle cells.
High energy demand and potential for medicine
Through this system of heat generation, the cute fur animals apparently get along with the low water temperatures in their habitat. This is also the cause of their well-known large appetite, explain the scientists: Sea otters eat marine animals every day, the total mass of which corresponds to a quarter of their own body weight. They apparently use a large part of this food to fuel their internal heating.
Wright and his colleagues are now planning to uncover further details of this system: “So far we have only taken a first look at the metabolism of sea otters. For example, it still remains unclear whether all muscle types in these animals have the same characteristics or whether other types of tissue also have an increased ability to generate heat, ”says Wright. Another question that may be important for medicine is how sea otters regulate their muscle metabolism in order to turn up the internal heating when necessary. “The regulation of tissue metabolism is also an important area of research in the fight against obesity,” said Wright. “These animals could give us clues as to how the metabolism of healthy people and those with diseases that affect muscle metabolism could be influenced,” says the scientist.
Source: Texas A&M University, Article: Science, doi: 10.1126 / science.abf4557