20 August 2012

Ocean Giants

Throughout its history Earth has been home to animals of epic proportions. These monsters have included dragonflies the size of small planes, dinosaurs that were so big that the very ground trembled when they walked and huge land mammals such as the woolly mammoth, which were actually seen by early man! Most of these colossal animals are now extinct however, with only the occasional over-sized fossil being found as the the only indication that they ever even existed. Despite the loss of these species, Earth is still filled with giants and none are bigger and heavier than the whales. 

10: Gray whale - 45 feet/40 tonnes

The gray whale, Eschrichtius robustus, is the only surviving member of its family,  Eschrichtiidae, which first appeared  over 30 million years ago. Gray whales were nicknamed devil fish during the whaling era because of their violent behaviour when hunted.

Gray whales are famous for their 14, 000 mile (22, 000 kilometre) migration route that takes them from the Bering and Chukchi Seas in the summer to Mexico over the winter. This route was once believed to have been the longest migratory journey undertaken by any animal, but recent evidence now suggests that some humpback whales can travel even further!

9: Sei whale - 48 feet/45 tonnes

The sei whale, Balaenoptera borealis, is one of the fastest species of cetaceans (the family of whales, dolphins and porpoises) and has been recorded swimming at speeds of 30 mph (50 kph).

Sei whales need to consume nearly 1, 000 kilograms of copepods (small crustaceans), krill and zooplankton every day in order to meet their energy requirements. Sei whales are a type of baleen whale, which means that they eat by filtering the organisms out of the water as they swim. Sei whales can be found in most of the world's oceans, although they are not found in polar waters.

8: Humpback whale - 45 feet/48 tonnes

The humpback whale, Megaptera novaeangliae, is easily identifiable by its  knobbly head and unusually long pectoral fins. Male humpbacks produce one of the most complex songs out of any whale species, which can last for as long as 20 minutes and are often repeated for hours at a time. Although the function of their songs is not conclusively known, it is believed that they have a role in attracting a mate.

Humpback whales are one of the most wide-spread species of whale and can be found throughout the world's oceans. They have an intensive migration route and travel over 16, 000 miles (25, 000 kilometres) a year from the cold polar waters where they spend their summer to the tropical or subtropical waters where they breed and give birth in the winter.

7: Sperm whale - 50 feet/60 tonnes

The sperm whale, Physeter macrocephalus, is the largest living species of toothed animal and has the  largest brain of any animal in the world.

Sperm whales feed predominantly on giant squid, which they dive for to depths of up to 3 kilometres. This feat makes them the deepest diving animal and they navigate in the complete darkness using echolocation. The clicks that they produce  for their echolocation have a range of 60 kilometres and are the loudest sound produced by any animal.

6: Bowhead whale - 55 feet/75 tonnes

The bowhead whale, Balaena mysticetus, lives in the frigid waters within the Arctic Circle. In order to keep warm here the whale has a huge layer of blubber that accounts for up to 50% of its total body mass.

Bowhead whales are unique among mammals because their bones never fuse. This means that they keep growing throughout their entire lives and individuals as long as 70 feet have been found (although this post uses the average length of each species, else it would be higher up the list). Remarkably bowhead whales are believed to live for over 200 years due to their low body temperature and females have been found over the age of 100 that are still fertile!

5: North Atlantic right whale - 52 feet/100 tonnes

With only 400 individuals of the species left in existence, the North Atlantic right whale (Eubalaena glacialis) is one of the most endangered whales in the world. This is despite its protection under the Marine Mammal Protection Act of 1972 and the U.S. Endangered Species Act of 1973.

Like all right whales, North Atlantic right whales can be distinguished by their broad back that lacks a dorsal fin and the callosities (thickened skin) above its eyes.  They continuously feed on copepods and other small invertebrates such as krill, pteropods and larval barnacles by skimming them out of the water and migrate from the Gulf of Maine to their calving areas off Georgia and Florida in the winter.

4: Finback whale - 90 feet/74 tonnes

The finback whale, Balaenoptera physalus, is also called the fin whale, razorback whale or  the common rorqual.  It is  the second longest animal in the world, but its thin body means it is lighter than some species of much shorter whale.

Finback whales feed off schooling fish, squid, crustaceans and krill and are unbelievably fast. So fast in fact, that they are faster than the quickest ocean steamship! This attribute has earned them the esteemed title of being the 'greyhounds of the sea'.

3: Southern right whale - 58 feet/110 tonnes

The Southern right whale, Eubalaenna australis, is recovering well since it became protected in 1937 and is now classified as being of 'Least Concern' by the IUCN, with its population growing by an estimated 7% each year.

Southern right whales spend much the summer close to Antarctica where their calves are safer from being predated by killer whales and great white sharks. During the winter, when the conditions of Antarctica become too harsh for them to remain there, they migrate north to the warmer waters of Argentina and seem to spend many hours in a unique behaviour called 'sailing'. This behaviour is believed to be recreational and consists of the whales catching the wind in their flukes and letting it propel them through the water like  boats!

2: North Pacific right whale - 60 feet/120 tonnes 

The North pacific right whale, Eubalaena japonica, feeds mainly on copepods that it constantly filters out of the water while swimming. Its prey is so small that it needs to consume millions of them each day in order to provide the energy that it needs to survive.

Unlike many other species of whale, the North Pacific right whale does not seem to have a clear migratory pattern and the only notable annual difference in their distribution is when they are breeding, where they tend to move closer inland.

1: Blue whale - 100 feet/190 tonnes

The blue whale, Balaenoptera musculus, is a peaceful whale that eats krill - one of the smallest organisms on the planet. Although there were once believed to have been 200, 000 blue whales in the oceans, it is estimated that there are now only 10, 000 left due to their historical over hunting. Sadly, and despite now being protected, their numbers are not expected to recover due to their slow life cycles.

As far as we know the blue whale is the largest animal that has ever lived on this planet and is twice the weight of the biggest known dinosaur. In fact, blue whales are so big that their tongues alone can weigh as much as an elephant and their hearts as much as a small car!

18 August 2012

Skinchangers: fact or fiction?

Throughout much of sub-Saharan Africa a disease called African trypanosomiasis (or sleeping sickness) is rife that affects both humans and animals alike. The main characteristic of the disease is the disruption of sleeping patterns that causes suffers to be awake at night and asleep during the day. Other symptoms of sleeping sickness include fever, sweating, headaches and the tendency to experience rapid mood swings. If the disease is left untreated, those infected with sleeping sickness could die from heart failure within 6 months of infection and, even if they get medical help in time, are likely to suffer from permanent damage to their nervous system so that their ability to live a normal life is impinged. Over 60 million people are at risk from African trypanosomiasis, which affects 50% of people in endemic areas. Furthermore, the loss of domestic cattle has had significant socio-economic consequences and the reduced ability for cattle farming has cost a staggering US$12, 000 million!

African trypanosomes are extracellular parasites, which means that they live freely in their hosts blood rather than inside of cells. Humans can be infected by two types of African trypanosome: Trypanosoma brucei gambiense and Trypanosoma brucei rhodiense, which is the most common and most deadly type, and is featured in this photo.

Sleeping sickness is spread by blood-sucking tsetse flies, which inject parasites called African trypanosomes* into their host's bloodstream along with the anticoagulants in their saliva. Once inside their host's bloodstream the parasites rapidly divide by binary fission and spread through various fluids throughout their body. What is interesting about African trypanosomes is the fact that they remain free-living in their host's body throughout their entire life cycle. This is highly unusual and most parasites (with the exception of worms), are intracellular and invade a specific type of cell to live and divide in as soon as they enter their host. The main reason many parasites do this, to put it simply, is to avoid their host's immunodefences. It is quite remarkable that African trypanosomes can manage to survive in the bloodstream,  which is a very hostile environment that is full of leukocytes (white blood cells)!

How they survive here is amazing and African trypanosomes are quite literally skinchangers! The parasites have special proteins on the surface of their 'skin' called variable surface glycoproteins (VSGs), which are encoded for by over 1, 000 different genes. The many proteins produced by these genes can be spliced together at random so that an infinite number of unique VSGs can be produced. This plays havoc for the host's defences and effectively renders the infection unclearable. This is because our immune system relies on shape: foreign invaders (or pathogens) have very specifically shaped antigens on their surfaces to which our bodies produce antibodies against in order to kill them. So, by changing the VSGs that they are displaying, African trypanosomes prevent their host's immune system from killing them off.

To explain this further, most of the parasites display the same unique VSG on their surface that their host's body cannot fight against so that they can divide unchecked. Eventually, and after a delay, the host's immune system produces new antibodies against this VSG and all of the parasites expressing that particular phenotype are killed. However a small number of the parasite population have already changed their skins by then and survive. These parasites then divide very rapidly (as they have less competition with other parasites), until the body 'learns' how to kill them and the whole cycle starts again. Eventually the parasites have done so much damage to the host, that it dies. Thus, outside medical treatment is required to kill all of the parasites at once that entails using powerful drugs such as Pentamidine or Melarsoprol.

The population of African trypanosomes in their host's bloodstream cycles depending on whether their host can kill them off or whether it is trying to produce new antibodies against them. The peaks in their population, which coincide with peaks in the symptoms of the disease, are called trypanolytic crises and were first discovered in 1910 by an Italian doctor.

So there you have it! African trypanosomes quite literally change their skin to avoid being detected and killed by their host's immune system, which allows them to persist in their host's body nearly indefinitely. 

* note that African trypanosomes are fundamentally very different to their cousins, South American trypanosomes, which cause Chagas Disease and have very different life cycles.

6 August 2012

Sleep: what is it & do we really need it?

In his novel The Wise Man's Fear, Patrick Rothfuss says that "you never really appreciate sleep until you wake up". He makes a good point here, as we often don't want to sleep even though we know that we'll be bad tempered, tired and miserable over the next day as a consequence. This is mainly because we have better, more interesting things to do so spending 8 - 10 hours asleep* seems like a pointless waste of our valuable time. However, as we all know, sleep is essential and shouldn't really be cut back on unless it's completely unavoidable. For example, sleep allows the levels of neurotransmitters in our brains to recover after a hard day's activity, allows us to repair damaged tissue and is even an essential factor for effective weight loss!

In order to fall asleep your core body temperature must drop. Sadly, this means that the traditional British tradition of taking a 'nightcap' of a spirit before bed actually makes it harder to fall asleep as alcohol raises the core body temperature.

As you would expect for such an obviously important biological process then, sleep has been extensively researched for decades. Much of this research has been fairly mundane, revealing fairly obvious facts like our sleep cycle runs as a circadian rhythm (one that repeats itself every 24 hours) and that lack of sleep has negative effects, such as reducing our mental and motor functions; our ability to cope with new and unexpected situations/events; and (usually), causes us to put on weight. Other areas of research however have been much more interesting and have yielded more titillating results.

Research into the sleep cycle itself is one such area, and has found that humans have 5 different stages of sleep. These stages fall into two major categories: Non-Rapid Eye Movement (NREM) sleep, which is sometimes called 'quiet sleep' and Rapid Eye Movement (REM), which is also called 'active' or 'paradoxical sleep'. NREM sleep consists of 4 of the 5 stages of sleep, which are designated as Stage 1, Stage 2, Stage 3 and Stage 4 respectively. REM sleep, which is arguably the most important state, only forms our final and deepest stage. Our bodies cycle through these stages over the period that we are asleep, with each stage being significantly 'deeper' than the one before it. Obviously then, we are much more awake in the earlier stages than in the latter, which is mainly due to differences in the brainwave patterns used by our brains. The earlier stages produce short, fast brainwaves called beta waves, which eventually progress into slower alpha waves. During these early stages, when you're not quite asleep, many people experience intense sensations called hypnagogic hallucinations. These are perfectly normal, and common examples include the sudden sensation of falling and hearing someone calling your name. Many people also experience sudden starts in the early stages, where they wake up with a twitch for no apparent reason. These starts are called myoclonic jerks and are not a cause for concern in most cases.

It is worth noting however that the body does not progress through these stages sequentially and upon falling into sleep, the body enters Stage 1. After this it progresses through to Stage 2, Stage 3 and Stage 4, which makes sense really. However, before entering REM, the body reverts back into Stage 3 and then Stage 2. It is only after reaching Stage 2 for its second time that the brain jumps directly into REM sleep. After the body has finished with REM sleep it returns back to Stage 2, which forms one complete cycle and typically takes 90 minutes. Our bodies typically undergo 4 or 5 of these cycles every night (consecutively) and spend more time in REM and less time in NREM sleep with each cycle. Thus, the body spends only a short amount of time in REM at the beginning of the night, but by the end, can be in it for up to an hour at a time.

The invention of the electroencephalograph in 1924 allowed scientists to see a person's brainwaves in real-time. Thus, it allowed them to study sleep as they never could have before and led to the discovery of the 5 stages of sleep.

Although this sleep cycle seems overly elaborate and pointless (as we're only asleep), it is actually very clever and each stage has its own characteristics and biological functions. Stage 1 for example, can be considered as our gateway into and out of sleep and typically lasts for only 5 - 10 minutes. Stage 1 is characterised by high amplitude theta waves in the brain, which are a very slow type of brainwave and, if a person is woken during this stage, they probably won't even realise they were asleep because their brainwaves are very similar to those displayed when they are awake.

Stage 2 last for up to 20 minutes and can be compared to a 'track changer' on a rail-road system and directs our brainwave patterns back into Stage 1 (so that we wake up), further in NREM sleep or deep into REM. Therefore Stage 2 effectively controls the sleep cycle and is characterised by the appearance of rapid, rhythmic bursts of brain activity called sleep spindles. It is in this stage that our core body temperature and heart rate begins to drop, which lowers our metabolism and energy consumption to allow our breathing to slow.

Stage 3 is a transitional period between light and deep sleeps and is marked the the appearance of delta waves, which effectively prepares our minds for low-intensity dreaming. Stage 4 follows on shortly after the appearance of delta waves, and is the first stage in which we dream. Stage 4 typically lasts for about 20 minutes and is the most likely stage for bed-wetting and sleepwalking to occur in.

Most of our dreaming occurs in REM, which, as mentioned before, is our final and deepest stage of sleep. This also explains why we rarely remember of dreams in REM even though it is here that they are at their most vivid - our brainwaves are so completely different to the patterns our brains use when we are awake, that they are almost completely incompatible with each other! Think of the difference between video cassettes and DVDs, which both show the same media despite doing in completely different ways...

Bizarrely our bodies actually become more active in REM sleep than in NREM, which is why it is sometimes called 'paradoxical sleep'. This can be seen just by looking at someone in REM as their eyes flick around in their sockets very rapidly, which gives the stage its name. To prevent people thrashing around in their beds and acting out their dreams our bodies employ a clever trick: they secrete a chemical that paralyses all of our voluntary, skeletal muscle so that we are unable to move!

Alarm clocks that wake you up using light are much better since they cause your brain to cycle down through its sleep cycle so that you wake up directly from Stage 1. This is the 'natural' way to wake up and leaves you feeling alert and fresh, as if you'd woken up by yourself. Sound alarm clocks can wake you abruptly from any stage, which is a problem when you are woken from the deeper states. This is because the deeper states have brainwave patterns that differ greatly to waking patterns, so that you feel groggy and disorientated for a time until they have changed.

An addition to understanding what goes on when we sleep, much research has also begun to unravel why we need to sleep in the first place, finding it to be essential for our long-term health. There are three main theories of why we sleep that do not have antagonistic values with each other, so may all be correct to varying degrees. The first, and probably most accepted theory, is called the 'Repair and Restoration Hypothesis'. This theory suggests that our bodies use sleep to heal and repair any damaged tissues and restore all of the physiological processes that allow our bodies and minds to function efficiently. Studies into this theory have found that people spend more time sleeping after periods of strenuous mental or physical activity, which would be expected really if our bodies were indeed healing during sleep. Research has found that the body greatly increases the rate of cell division and protein synthesis during NREM sleep, which is essential for growth (in a child) and for repairing physical trauma. Evidence also suggests that the high brain activity seen in REM sleep allows the body to replenish and 'restock' its levels and reserves of neurotransmitters so that the brain can function more easily and efficiently the next day.

The second major theory of sleep suggests that it is a mechanism for the brain to make sense of and store all of the information and events that it has been exposed to throughout the day into the brain's long-term memory. This is called the 'Information Consolidation Theory of Sleep' and research has provided much evidence that supports it.

Many students, particularly when at university, pull 'all-nighters' where they spend as much of the night as they can revising for their exams. This is actually detrimental to their learning efforts and makes them much less likely to remember what they've read. Having an early night greatly increases the likelihood of the information they've revised earlier being stored and makes it easier for them to think the following day.

The third and final of the major theories is called the 'Evolutionary (or Adaptive) Theory of Sleep' and suggests that sleep is used as a mechanism for conserving energy (due to decreased physical activity) during periods in which it would be dangerous for that animal to be active in, such as at night in humans due to our relatively poor ability to navigate our environment in the dark. The main support for this theory comes from the fact that animals with few or no natural predators, such as lions, sleep for much longer periods of time than those with many predators, such as mice, which only sleep for a few hours a day.

So, it is obvious that sleep is an essential and a very important process for our health. It allows us to conserve energy, repair damaged tissue, helps us to form long-lasting memories and helps to us prepare for the days to come. Skipping sleep in favour of other, more interesting activities, really isn't a good idea and you should ensure that you are getting the amount of sleep that your individual body requires each night. All of the sleep-deprivation studies to my knowledge associate a lack of sleep with direct, negative side-effects that can easily be avoided.

* on average, depending on your age.