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!

The icefish: life without respiratory pigments

Wherever you look for life on Earth, you find it. From free-floating bacteria in the upper atmosphere to tiny organisms that make their home deep within the solid crust of its surface. Animals have been found thriving in deserts hot enough to cook them alive and, similarly, have been recorded living abundantly in environments that are cold enough to freeze their bodies solid!

Living in such hostile conditions places huge strains on the organisms that live there, which, as a necessity, have had to evolve specialised physiological adaptations if they are to survive for long enough to reproduce and pass on their genes. There are many examples of extreme and unique adaptations for this purpose, with those of the Antarctic icefish being among the most bizarre.

Icefish are found throughout the cold waters that surround Antarctica and South America, belonging to the Channichthyidae family - a small group of fish that have no respiratory pigments in their blood. 

Rather uniquely among species of animals, Antarctic icefish do not rely on respiratory pigments to carry oxygen in their blood and lack them altogether! Such respiratory pigments were once believed to be essential for multicellular life to exist since they chaperone oxygen so that it can be removed from the air and absorbed by the blood, where it is at a much higher concentration than in the surrounding atmosphere. This is an important 'law' that life must overcome if it is to grow bigger than a single-celled organism because molecules naturally diffuse from an area of high concentration to one of a low concentration and not the other way around! So, simply put, without respiratory pigments the oxygen content of blood would be too low to fuel life as we know it!

Thus, the vast majority of multi-celled organisms have blood that is packed with respiratory pigments. These pigments are usually constructed from 1 of 2 key metals, with which one being used depending on an organism's evolutionary history and can be used to synthesise a number of different pigments:

• Iron, which is the most common basis of respiratory pigments, can be used to produce:
• Haemoglobin, which is found in humans and turns red when oxgenated.
• Hemethryins, which are found in terrestrial worms and brachiopods, and turn violet when oxygenated.
• Chlorocruorin, which is found in aquatic worms and turns green when oxygenated.
• Copper, which is used to make hemocyanins. Hemocyanins are blue when oxygenated and are usually found in families of molluscs and arthropods.

The fact that icefish lack such respiratory pigments is puzzling at first glance, but actually makes sense when it is considered carefully since it provides the fish with a huge advantage in their ability to survive in the harsh cold of Antarctica. Basically this advantage stems from the fact that the colder water is, the more oxygen can dissolve in it. Thus, the frigid Antarctic waters carry much more oxygen than warmer waters do so icefish breathe in more oxygen with each 'breath'. This, coupled with the fact that they have twice as much blood fluid in their body than another species of fish their size, means that they can still provide their muscles with enough oxygen to work effectively.

But why is this advantageous to their survival? Well, the fact that icefish can supply enough oxygen to their muscles in order to survive without respiratory pigments means that they do not have to make any; saving them huge amounts of energy each year that can be used for more useful tasks instead, such as feeding, reproducing and evading predators!

Furthermore having no respiratory pigments in their blood decreases its overall viscosity by about 25%, which means that their heart has to work far less hard to pump blood around their body than it otherwise would have. In addition to placing less strain on the organ so they can live for much longer before it gives out, having thinner blood also reduces their energy expenditure and allows them to move 4 times more blood which each beat than a typical fish their size - saving even more energy!

Thus, the icefish has evolved to possess one of nature's most bizarre and unprecedented adaptations that allows it to thrive in one of the most extreme environments on Earth! Without this adaptation, or another that gave it a similar advantage, the strange fish would have undoubtedly died out long ago, being unable to to survive and reproduce in the freezing waters of the Antarctic...