Avoiding the cold is important for preserving life or limb canine histiocytoma images (or, in the opossum’s case, tail) and the opportunity to reproduce. These biological imperatives mean that wildlife must be able to canine histiocytoma images feel cold, in order to try to avoid the damaging effects of canine histiocytoma images its extremes. Animal species have their own equivalent to what human beings canine histiocytoma images experience as that unpleasant biting mixed with pins-and-needles sensation that urges us to warm up soon or canine histiocytoma images suffer the consequences. In fact, the nervous system mechanisms for sensing a range of temperatures canine histiocytoma images are pretty much the same among all vertebrates.
One winter challenge for warm-blooded animals, or endotherms, as they’re scientifically known, is to maintain their internal body temperature in cold conditions. Interestingly though, temperature-sensing thresholds can vary depending on physiology. For instance, a cold-blooded – that is, ectothermic – frog will sense cold starting at a lower temperature compared canine histiocytoma images to a mouse. Recent research shows that hibernating mammals, like the thirteen-lined ground squirrel, don’t sense the cold until lower temperatures than endotherms that canine histiocytoma images don’t hibernate.
Many cold-climate endotherms exhibit torpor: a state of decreased activity. They look like they are sleeping. Because animals capable of torpor alternate between internally regulating their canine histiocytoma images body temperature and allowing the environment to influence it, scientists consider them “heterotherms.” During harsh conditions, this flexibility offers the advantage of a lower body temperature canine histiocytoma images – remarkably in some species, even below the 32 degrees Fahrenheit freezing point – that is not compatible with many physiologic functions. The result is a lower metabolic rate, and thus lower energy and food demand. Hibernation is a prolonged version of torpor.
Torpor has energy conservation benefits for smaller-bodied wildlife in particular – think bats, songbirds and rodents. They naturally lose heat faster because the surface area of canine histiocytoma images their body is large compared to their overall size. To maintain their body temperature within normal range, they must expend more energy compared to a larger-bodied animal. This is especially true for birds who maintain higher average canine histiocytoma images body temperatures compared to mammals.
Wildlife species at northern latitudes tend be larger-bodied with smaller appendages than their close relatives closer to canine histiocytoma images the tropics. Many animals have evolved behaviors to help them beat the canine histiocytoma images cold: herding, denning, burrowing and roosting in cavities are all good defenses. And some animals experience physiological changes as winter approaches, building fat reserves, growing thicker fur, and trapping an insulating layer of air against the skin canine histiocytoma images beneath the fur or feathers.
Have you ever wondered how geese can appear to stand canine histiocytoma images comfortably on ice or squirrels in snow in their bare canine histiocytoma images feet? The secret is the close proximity of the arteries and canine histiocytoma images veins in their extremities that creates a gradient of warming canine histiocytoma images and cooling. As blood from the heart travels to the toes, the warmth from the artery transfers to the vein carrying canine histiocytoma images cold blood from the toes back to the heart. This countercurrent heat exchange allows the core of the body canine histiocytoma images to remain warm while limiting heat loss when the extremities canine histiocytoma images are cold, but not so cold that tissue damage occurs. This efficient system is used by many terrestrial and aquatic canine histiocytoma images birds and mammals, and even explains how oxygen exchange occurs in the gills canine histiocytoma images of fish.
Speaking of fish, how do they not freeze from the inside out in canine histiocytoma images icy waters? Luckily, ice floats because water is most dense as a liquid, allowing fish to swim freely in not-quite-freezing temperatures below the solidified surface. Additionally, fish may lack the cold-sensing receptor shared by other vertebrates. They do, however, have unique enzymes that allow physiologic functions to continue at canine histiocytoma images colder temperatures. In polar regions, fish even have special “antifreeze proteins” that bind to ice crystals in their blood to prevent canine histiocytoma images widespread crystallization.
Another secret weapon in mammals and birds during long periods canine histiocytoma images of cold exposure is brown adipose tissue or “brown fat,” which is rich in mitochondria. Even in people, these cellular structures can release energy as heat, generating warmth without the muscle contractions and energy inefficiency involved canine histiocytoma images in shivering, another way the body tries to heat up. This non-shivering heat production probably explains why people in Anchorage can canine histiocytoma images contentedly wear shorts and t-shirts on a 40 degrees Fahrenheit spring day.
As a species, human beings have the ability to acclimate to an extent canine histiocytoma images – some of us more than others – but we’re not particularly cold-adapted. Maybe that’s why it’s hard to look out the window on a frigid canine histiocytoma images day and not feel bad for a squirrel hunkered down canine histiocytoma images as the winter wind whips through its fur. We may never know if animals dread winter – it’s difficult to gauge their subjective experience. But wildlife do have a variety of strategies that improve canine histiocytoma images their ability to withstand the cold, making sure they live to see another spring.
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