Living with extreme temperatures: water bear and ground squirrel
When looking at the temperature, there are hardly any animals that can get a body temperature below 0 degrees. A temperature below zero causes all kinds of problems. That makes the water bear extra special: the animal can survive temperatures of -270 degrees Celsius. In addition to this special organism, there is also a mammal that can get a body temperature of below 0 degrees, the Alaskan ground squirrel!
The Alaskan ground squirrel
The Alaskan ground squirrel is a special mammal, as it can bring its body temperature below zero. This makes it the mammal that can have the coldest body temperature, often as low as -3 degrees Celsius. The ground squirrel in question lives in Alaska, where it can get very cold in the winter. Keeping a body warm takes a lot of energy. The greater the difference in temperature, the more energy is needed to keep the animal at the right temperature. For example, when the ambient temperature in winter is -25 degrees, and the ground squirrel’s body temperature is 20 degrees, it takes a lot of energy to maintain this body temperature.
Food is needed for so much energy, but food is very scarce in the winter in Alaska. In order to be able to live under such conditions, the temperature of the animal must therefore fall below 0 degrees. The difference between the body temperature and the outside temperature is then much smaller. To withstand a low body temperature, the animal made adjustments. After all, the moisture in the ground squirrel’s body must not freeze, which would have fatal consequences. The ground squirrel’s temperature cannot drop below -3 degrees, so energy is still required. The ground squirrel gets this energy from the brown fat. We also see this type of fat in the bodies of other newborns and other animals that go into hibernation. The advantage of the brown fat is that it does not freeze at -3 degrees, so it remains usable. Brown fat cells contain fewer mitochondria than other body cells. Because there are fewer mitochondria present, a different process than normal takes place. In this process, called uncoupled oxidation, fatty acids (from the brown fat) are converted into carbon dioxide, water and heat. The advantage of decoupled oxidation is that more heat is created than ATP (a carrier of energy).
Not everything is known yet about the Alaskan ground squirrel. For example, the animal emerges from its burrow after about three weeks during its hibernation. Above the ground, the animal warms up to a temperature of just over 36 degrees. Twelve hours later the ground squirrel cools down and goes back into the ground. Scientists think ground squirrels do this to stay in REM sleep. During REM sleep, the squirrel does not actually sleep, but is more in a resting state.
The water bear
The water bear is a very small creature, the animal is between 0.1 and 1.5 mm in size. The aquatic animal is not one species, it is a tribe of different classes. So there are different classes and types of water bears. Research indicates that there are about 760 species in this group. For the most part, the species are similar, so general aspects of the water bear can be discussed.
Such a small creature would be expected to have a simple structure. Still, the water bear has eyes, a mouth and digestion. As the name implies, the water bear likes humid environments. It does not place much demands on its environment, they can be found all over the world: from freshwater to saltwater, from high temperature to extremely low temperatures. Great heights (such as the Himalayas) or extreme depths (deep seas) do not deter the water bear either.
In order to survive, the water bear has developed a mechanism. They can be suspended animation. If conditions are extreme for a long time, we speak of temperatures as high as -270 degrees, they shrivel themselves. The animal’s legs then disappear, but once the animal is in contact with water again, they can become active again in a few hours.