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Is a dog warm or coldblooded?

Dormancy in cold-blooded vertebrates

African lungfish

Two kinds of dormancy can be distinguished in vertebrates on the basis of body temperature. Most vertebrates are poikilothermous, or cold-blooded, because the body temperature follows that of the environment and is not kept constant by internal (homoiostatic) mechanisms. The second group, the homoiotherms, maintain a constant body temperature regardless of the ambient temperature; these warm-blooded animals include birds and mammals.

Fishes and amphibians

The metabolism of poikilothermous animals is most influenced by the environmental variables of temperature, nutrition, and photoperiod. Photoperiod, the daily length of light exposure, has a marked metabolic effect in both fishes and amphibians; fishes, however, remain active throughout the year, although the activity may be limited by temperature, as in those fish that rest on the bottom or in mud during cold periods. Brief superficial freezing and supercooling (without freezing) to temperatures below the freezing point of body fluids are experienced by resistant species, but it has not been established that fishes that have been frozen solid can become active when thawed. In the Arctic, no fishes are found in lakes that freeze solid in the winter. Because most fishes do maintain some kind of activity year round, they cannot be said to become dormant in the sense in which the word is used in this article.

In addition to light and temperature, another environmental stress imposed upon fish is drought. Lungfishes, as represented by the African lungfish (Protopterus), burrow deeply into the mud when their water supply is diminished. They surround themselves with a cocoon of slime and remain inactive. Their gills are nonfunctional during this period of dormancy, and they use a lunglike air bladder for respiratory purposes. They rely on fat reserves as an energy source, and in order to conserve water, they excrete urea rather than ammonia. This is because ammonia as an excretory product is highly toxic; animals that excrete ammonia require large quantities of water to dilute it below toxic levels. Urea is a semi-solid substance of low solubility, and requires little or no water for its excretion. (Desert animals and many insects excrete urea.)

Know how hibernating frogs survive in freezing temperatures

During periods of drought or cold, amphibians seek protective niches in which to remain dormant until the return of favourable environmental conditions. Overwintering of frogs and salamanders frequently involves their aggregation in large numbers in a moist terrestrial niche, such as a rotting log, the mud on banks or bottoms of marshes and ponds, or in springs. The more terrestrially oriented amphibians, such as toads, may pass the winter in solitary burrows on land. During dry seasons, frogs may be dormant in a mud cocoon.


Effects of temperature

Because reptiles depend on external sources of heat to keep warm, they survive during periods of low temperature by seeking a place where the temperature will not fall below freezing, except temporarily. The commonest niche for reptilian dormancy is almost always found underground at a depth dependent on the thermal conductivity of the soil relative to the minimum temperature reached. This factor alone can control the distribution of reptiles. None can survive in the Arctic or Antarctic in places in which the subsoil is permanently frozen; and relatively few can exist in areas near these regions, even if suitable sites for dormancy were available, because the short summers would prevent the completion of life cycles. Although the distribution of snakes at high latitudes or altitudes is limited, the adder has been found at 3,300 metres (10,000 feet) in the Swiss Alps and as far north as the Arctic Circle. The Himalayan pit viper has been found at an altitude of 5,000 metres (16,000 feet).

Winter dormancy in reptiles, which is also called brumation, is akin to hibernation in mammals. Instead of experiencing long, sustained periods of inactivity, brumating reptiles stir occasionally to drink water; however, they may go without food for several months. Dormancy in reptiles may display a circadian rhythm, a seasonal one, or both; it is a state of torpor directly induced by low temperature. When the adder, for example, experiences temperatures of about 8–10 °C (46–50 °F), it begins to search out suitable niches in which to rest. Its dormancy ends on the first sunny days after the maximum temperature has reached 7.5 °C (45.5 °F). Because these conditions vary, the adder’s period of dormancy extends from 275 days in northern Europe to 105 days in southern Europe and is about two weeks in the United Kingdom, where the Gulf Stream provides warmth.

Reptiles also normally become dormant during the hottest parts of summer, but the physiology of summer dormancy is quite different from that of winter. As already mentioned, winter dormancy is a state of torpor, induced by a low temperature, that becomes more pronounced as the temperature falls. There is, however, a wide range between the animal’s normal, active (coenothermic) temperature and the lowest temperature at which it can exist. At high temperatures, on the other hand, there is a much narrower range between the coenothermic temperature and temperatures that cause death. In other words, reptiles can tolerate colder temperatures much better than they can tolerate higher ones. For this reason, during hot weather they must seek refuge underground or in cool, shady places, where they remain physiologically active but must forego all normal activity because of the restricted nature of the cooler niche. Desert reptiles, in particular, exhibit such temperature responses daily.

During its dormancy, the amount of water needed by a reptile is less than at other times and is normally supplied by water produced from the metabolism of the animal’s own stored food reserves, particularly fat. In areas in which alternating wet and dry seasons occur, reptiles maintain a longer period of dormancy during the dry season. This behaviour may be related more to the lack of available water than to temperature, because in such areas the onset of the seasonal monsoons elicits a period of increased reptile activity.

Because there is only a limited number of suitable sites available for dormancy, several snakes, usually of the same species, may be found in each niche. As many as 100 or more snakes have been taken from one winter den. Occasionally, lizards and toads may also be found in the same den, but stories of snakes that share denning sites with small birds and mammals have been difficult to substantiate. It is much more usual to find that the entry of snakes into the burrow of a prairie dog or some other warm-blooded animal is followed by the evacuation of the original occupant.

Effects of latitude

Changes in latitude not only alter the lengths of the dormant and active periods of reptiles but also affect their circadian rhythms because of the changes in the proportions of night to day. Many species of snakes, including the adder, are normally active in the early evening. In the northerly latitudes (e.g., northern Europe, such as Scandinavia and Finland), where the length of the active season is reduced by as much as two-thirds, these snakes are active throughout the day and are able to take advantage of every warm hour in order to complete the necessary portions of their life cycle. Even this increased activity during the shorter summer season, however, does not compensate for the latitude. Growth and development slow to such a point that sexual maturity is delayed, and the reproductive period requires two years rather than one; young are produced only every other year instead of every year, as at lower latitudes.

Is a dog warm or coldblooded?

Why shouldn’t you put a blanket on a cold blooded animal?

Hi science fans, Mia here. Usually Bryan writes the blog posts but this topic is especially close to my heart, as someone who is a relatively recent convert to the joys of biology. Full disclosure, this question did not come from a child. It came from me, as a fully grown adult. Luckily I feel no shame at not knowing the answer to something – it is only when we accept our ignorance that we can learn.

Many years ago, Bryan and I adopted a bearded dragon and called him Bert. At the time I was a physics student who believed physics to be far superior to all other sciences, because it was logical and biology didn’t make any sense. Together, Bryan and Bert completely changed my mind.

Bert: the bearded dragon

Bearded dragons make awesome pets!

When tiny little Bert curled up and went to sleep on his first night in our home, I worried about him. His heat lamp had gone out and his vivarium temperature had dropped from around 35 degrees to less than 20 degrees. Proving my ignorance about living things once and for all, I turned to Bryan and asked, “should I get him a little blanket?”.

Bryan looked incredulous. “A blanket?”, he asked, “But he’s cold blooded!”.

A bearded dragon with his mouth open appearing to be laughing.

A blanket? On a cold blooded animal? Don’t make me laugh.

It was at that moment I realised that I had absolutely no idea what cold blooded meant. I remembered a lesson in school in which I memorised the sentence “Warm blooded animals are always the same temperature, and cold blooded animals are the same temperature as their surroundings”, but that didn’t explain what cold blooded meant, only how you could describe an animal that was cold blooded. The real answer is far more interesting and useful, and it is as logical as my beloved physics.

Living things are powered by chemical reactions. Chemical reactions cause muscles to contract, messages to be passed along the nervous system, and new cells to be built. These reactions require energy and chemical building blocks.

Cold blooded animals get the chemical building blocks and some of the energy from their food, but have to top up the energy by soaking up heat from their environment. As an example, after eating loads of locusts, Bert has to sit underneath his heat lamp and bask, otherwise his digestive system won’t have enough energy to digest the locusts.

In warm blooded animals something amazing has happened. We can break down food so quickly that we can warm ourselves up entirely by converting the energy in the food into heat – no need to sit underneath a heat lamp! Our food contains loads of energy that can be stored and released at our own leisure.

Two polar bears.

Polar bears can survive extremely cold conditions thanks to thick, insulating fur, amongst other key adaptations. Source: Pixabay

Being warm blooded is great because it allows us to survive away from the tropics. Polar bears can survive in the Arctic because they can release energy from their food in the form of heat. Warm blooded animals have gradually spread to colder and colder environments, specialising with adaptations like thick fur and blubber. Fur is a great insulator of heat, so when furry animals generate excess heat the fur prevents it from escaping, making them extra efficient at maintaining that optimal body temperature. We don’t have fur any more but at night time we can hold on to our excess heat by wrapping a blanket around us.

Meanwhile, our cold blooded friends don’t generate any heat from within. Wrapping them up in a blanket is not going to help them – if anything it will insulate them from outside heat, like a cold drink in a thermos flask – and prevent them from warming up. And that’s why you don’t put a blanket on a sleeping lizard.

Bearded dragon with a white handkerchief.

Bert does sometimes sleep underneath a blanket (yes, I was stubborn and gave it to him), but as far as we can tell, it seems to be a comfort/safety thing.

It’s worth mentioning that there are upsides to being cold blooded – so you don’t need to feel too sorry for poor Bert. Getting your heat energy from outside means you can eat a lot less food than us warm blooded creatures. We have to consume hundreds and hundreds of calories on a daily basis, whereas even the almighty komodo dragon (the largest lizard in the world) only has to eat around one large meal each month.

A komodo dragon, a very large lizard.

The almighty Komodo dragon. Source: Pixabay

Having a lizard has been a wonderful experience for me. Apart from being very cute and loveable he has inspired all sorts of questions that eventually persuaded me to switch to a biology degree. If you have a pet, encourage your child to question their behaviour, and compare the pet to themselves. Why does my dog have fur when I don’t? Why does my cat need to eat meat when I can be a vegetarian? Why does my rabbit eat its own poo? These are the questions that have inspired biologists for hundreds of years.

A bearded dragon sitting on a book as if he is reading it.

If you want to be good at biology, get a pet.

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