Life in the cold can be hard for animals. The brain and muscles slow down when the body is cold.
mammals can increase their metabolism to warm their body, but the temperature of their environment is the most important factor in determining their body temperature. They can live in colder areas and still be active during the winter.
Although mammals can increase their metabolism in the cold, scientists don't know which organs are using the extra energy to generate more heat.
We wanted to know how sea otter have adapted to survive the cold.
We assembled a research team with expertise in both human and marine mammal metabolism, including Mike Murray of the Monterey Bay Aquarium. Understanding energy use in animals adapted to life in the cold may provide clues for manipulating human metabolism.
Sea otter metabolism.
It is difficult for water-living mammals to stay warm because they can't keep their body temperature constant. A thick layer of fat or blubber is what most marine mammals have.
Sea otter do not have a thick layer of blubber. They are insulated by the densest fur of any mammal, with as many as a million hairs per square inch.
Regular grooming is required for this fur. A sea otter's daily activity involves maintaining the air trapped in their fur.
Sea otter fur is not enough to keep them warm. Their metabolism is three times higher than that of other mammals. The high rate of metabolism has a cost.
Sea otter must eat more than 20 percent of their body mass in food each day to get enough energy to fuel the high demand. Humans eat around 2 percent of their body mass, which is about 3 pounds of food per day for a 155-pound person.
Cells can't use the energy in animals' food to do work. The food is broken down into simple vitamins. The cells absorb the vitamins and minerals in the blood.
The cell has a high-energy molecule called the energy currency, which is converted into a high-energy molecule called the mitochondria.
Similar to how a dam turns stored water into electricity, the process of converting nutrients into ATP is similar. As water from the dam flows out, it makes electricity by spinning blades connected to a generator, like wind turning the blades on a windmill. Some water and stored energy can't be used to make electricity if the dam is leaking.
The lymphatics are less efficient at making the molecule. The leaked energy in the mitochondria can be used to warm the sea otter's body.
Some tissues are more active than others and use more energy. Most mammals have 30 percent of their body mass made up of muscle. When active, muscles produce a lot of heat. You have probably experienced this at one point or another.
We studied small muscle samples from sea otter pups to adults to find out if muscle metabolism helps keep the sea otter warm. We placed the muscle samples in small chambers to measure how much oxygen is used.
We determined how much energy the mitochondria could use by adding different solutions that stimulated or prevented various metabolism processes.
The sea otter's muscles could be very weak, which could allow them to turn up the heat without physical activity.
Sea otter muscle is good at being inefficient. They can survive the cold by losing heat and turning their energy into movement.
Newborn pups have the same metabolism as adults, even though they have not yet developed their muscles for swimming and diving.
Broader implications.
Our research shows that muscle is more important than just movement. Even a small increase in muscle metabolism can increase how much energy an animal uses.
Implications for human health are important. Doctors could potentially use this as a tool to increase the amount of calories a patient can burn if scientists were able to increase skeletal muscle metabolism at rest.
Reducing muscle metabolism could help patients suffering from cancer and other diseases, as well as reduce food and resources needed to support astronauts on long-duration spaceflight.
Texas A&M University has a research assistant professor and a professor of health and kinesiology.
The Conversation's article is a Creative Commons licensed one. The original article can be found here.
