25 December 2012

Surviving the cold

If you think that we have it tough in the winter and have an excuse to moan about the cold while we pass from one heated building to the next, bundled tightly in warm clothes and thick coats, then image how hard wild animals find it. There are no insects or berries for them to eat so food is scarce; there is little canopy cover in trees to hide from predators and keep the wind, rain and snow off them; and, to top it all off, they should be eating copious amounts of food just to keep warm!

Due to these rather brutal living conditions, animals have had to be clever in order to survive. Consequently,  they have had to perfect the use a range of physical and/or behavioural adaptations to give them the edge they need to keep one step ahead of the cold.

The most obvious of these adaptations are those that involve specialised behaviours, which typically involve migrating to warmer continents or hibernating through the inclement of winter until spring arrives, bringing  more hospitable weather with it and a much needed abundance of food!

Hibernation then, is essentially just a state of extremely deep sleep that aims to allow an animal to preserve as much energy as possible. In order to do this, a hibernating animal's brain activity drops to a very low level of activity (which is unusual for sleep) and their metabolism virtually stops - allowing them to save enough energy to survive until spring. The process is surprisingly efficient and, as such, scientists have recorded many species of animals that hibernate, although it is most commonly seen in mammals, such bears, bats and hedgehogs, and in certain species of insects, such as bumblebees.

Contrary to popular belief, most animals that hibernate do not sleep continuously and wake sporadically throughout their hibernation in order to defecate and (occasionally) to eat from their food reserves.  This photograph provides a good example of this, showing a doormouse hibernating with emergency hazelnuts close to hand.

For many animals however, hibernation isn't an option since it leaves such individuals very vulnerable to active predators and human disturbances, but they still lack the specialised physical adaptations (like thick coats) that are needed to keep them warm. These animals then, have chosen to simply 'opt out' of the cold winter months and migrate for thousands of miles each year until they reach warmer climates where food is still plentiful. Migration is particularly common in birds, such as house martins, swallows and swifts, and in many species of whale, such as humpback whales that can travel over 25, 000 kilometres a year!

Although many animals survive well using hibernation and migration, they are both extremely risky methods of enduring/avoiding the cold that are fraught with their own disadvantages, such as falling prey to storms while migrating over oceans and not being able to build up enough fat reserves in the spring to sleep through winter! Due to this, many animals not only opt to remain in cold areas, but chose to stay active and alert over the coldest months.

This has meant that many animals, especially species that live in the cold all year round, have evolved a wide range of physical adaptations that help to keep them warm. The most common of these, which has been mentioned above, is to posses a thick coat of fur (just look at the coats of wolves and reindeer), which acts as an excellent insulator against the cold by trapping layer of air above the skin. This layer of air gets warmed by the animal's own body heat and effectively acts as an electric blanket because it can't escape!

In addition to having a thick pelt that covers them, many animals that live in the cold have a thick layer of fat beneath their skin called blubber, which insulates heat and effectively acts as a 'blanket' that traps warmth inside their body. These layers can be extremely thick, with the 4 inch layer found in polar bears being a good example.

Many animals also possess other physical adaptations that are much less obvious since they involve internal changes rather than outside defences. A good example of this can be found in many species of fish that live in the Antarctic, which produce a natural 'antifreeze' in their blood that alters the way water molecules move in a manner that stops them from freezing. The antifreeze is made from glycoproteins, a very common class of biological 'building blocks' and is rather imaginatively called Antifreeze glycoprotein (AFGP), allowing fish to survive in extremely cold waters with a temperature far below 0C.

The wood frog, Rana Sylvatica, has a remarkable survival strategy to survive the winter and actually allows itself to freeze completely solid. As it freezes, the frog packs its cells with glucose and urea (found in urine), which helps to stop their cells from shrinking and splitting as they freeze. As much as 65% of their total body mass can freeze over winter; thawing out in the spring as if nothing has happened!

Many animals that live in algid climates also employ the use of specialised forms of mitochondria and enzymes, called isozymes or allozymes (depending on whether or not its gene is coded on the same chromosome as the original), which work much better at low temperatures than normal forms of enzymes do. Thus, the animal's body simply becomes better at functioning in the cold than it otherwise would have - providing them with a huge survival advantage.

In fact all animals, including humans, have many different isozymes and allozymes in their body that replace normal enzymes after spending a few weeks in a new climate. This is why we appear to 'get used to the temperature' when we move between seasons or go on holiday - unbelievably, we actually are getting used to it!

So there you have it - a few examples of the remarkable methods that animals have developed so they can  survive in (or avoid) the brutal conditions and biting cold of winter! I sincerely hope that you have enjoyed reading this post, along with all the rest in this blog, and hope that you continue to visit my site in the coming year! I already have a whole bunch of (hopefully) interesting ideas for articles and creature features planned for you!

Have a very Merry Christmas!

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