20 November 2012

Do we really eat spiders in our sleep?

Urban mythology claims that each year, a certain number of spiders crawl into out mouths while we are asleep and are consequently eaten. While the exact number of spiders that we are supposed to eat varies widely, the common theme remains the same and the stories usually suggest that there is nothing we can do to prevent this from happening.

Spider silk is one of most amazing chemicals in nature, being both incredibly light and having a tensile strength that is far greater than steel. In fact, the silk of the golden orb weaver (not shown above) is 6 times stronger than steel and is 10 times more efficient at absorbing energy than military-grade kevlar, being tough enough to capture bats and small birds!

Whereas it is doubtful that we could stop spiders from crawling or lowering themselves into our mouths if they wanted to (we are asleep afterall), there is actually no need as a spider would not be interested in creeping down our throats, so that in fact, we have nothing to worry about whatsoever!

This is mainly due to the content of our breath, which is warm, humid and has a much higher carbon dioxide to oxygen ratio than 'normal' air does. If a spider was crawling towards our mouth, it would sense such conditions when we breathed over it and would actively avoid them since they signal that the conditions within are mouth are harsher than those outside. Imagine, for example, smelling smoke coming from your living room - even if you couldn't see or feel the flames, you would know that something was wrong and that there may be a danger in the room. Thus, you would most likely avoid going in!

For similar reasons it is unlikely that a spider would want to enter your mouth and, if one was on your face, would probably turn tail and run once it came close enough to feel your breath!

17 November 2012

Better red than dead

Many people consider autumn to be the most beautiful season of the year, where the normally green leaves of trees take on striking hues of red and yellow and swathes of gossamer glitter in the morning dew. It is a season where both plants and animals brace themselves for the oncoming inclement of winter, and, as this post is written, is gripping the United Kingdom in full force.

As mentioned above, one of the of the most notable aspects of autumn is the colour change in deciduous leaves before they fall (via senescence). Whereas senescence may seem to be a waste of resources for a tree, as they will have to regrow their leaves in the following spring, it is actually a necessary stage in a clever life cycle that allows them to maximise their photosynthetic output during the summer. Simply put, their large, broad leaves are big enough to contain huge quantities of a pigment called chlorophyll, which captures the energy in sunlight and uses it to produce sugars and proteins (via photosynthesis). Thus, the leaves of deciduous trees can produce much more energy during the summer than the narrower, needle-like leaves of evergreen trees. Obviously, this is a huge advantage to a tree and will make them much more likely to survive during the spring and summer. However, to use an apt quotation from George R. R. Martin's A Song of Ice and Fire: "winter is coming", and this is where deciduous leaves hit their main problem - they are too big to defend against the cold. So, rather than allow their leaves to die and greatly increase their risk of infection, deciduous trees shed their leaves before they can be damaged by frosts; opting instead to regrow them next spring.

Autumn landscapes can be stunning, with leaves taking on a wide range of beautiful red and yellow hues.

The main problem that this tactic for survival has, is in the huge waste of the resources that a tree has invested in growing its leaves in the first place. For example, imagine how much protein and bone would be wasted if you shed your arm every year only to regrow it at a later date! Fortunately, it seems that deciduous trees became wise to this fact a very long time ago and, before they shed their leaves, they reabsorb much of the chlorophyll and useful proteins, which are then used to produce new leaves the following spring. In fact, it is this 'recycling' of chemicals and removal of leaf colouring pigments that produce the yellow colour of autumn leaves, which becomes more intense as more chemicals are stripped from its cells.

This is a very simple biological idea and has been accepted within the scientific community for decades. But, there is one aspect of senescence that is still widely disputed among plant physiologists and biologists alike - the reason behind the red colour of senescing leaves, which is produced by a class of pigment chemicals called anthocyanins. To briefly summarise the strife, many scientists are adamant that anthocyanins serve no function in senescence and believe that they are merely a waste product of reabsorbance; resulting from a complicated carbohydrate overflow process. Other scientists however, believe that is is not the case as anthocyanins are actually manufactured by trees via a very energetically expensive process; thus, arguing that they must serve a specific function or they wouldn't be produced.

This idea is supported by recent research, which indicates that anthocyanins may be crucial for the survival of a deciduous tree. Within this research, there are 2 major theories that offer explanations for the presence of anthocyanins:

  • The first, purposed by Taylor S. Feild, suggests that anthocyanins act as optical screening pigments to protect chloroplasts from being damaged by destructive ultraviolet (UV) radiation, which effectively counters the reabsorbance of normal screening pigments and allows leaves to photosynthesise for longer.
  • The second, developed by the famous geneticist William D. Hamilton, is called the 'coevolution theory' and argues that the bright red displays are produced by deciduous trees as a warning to deter destructive aphids that colonise them throughout autumn.

The first theory works using the knowledge that UV radiation is just as dangerous to trees as it is to human skin and, in accordance with this, plant physiologists discovered long ago that trees produce screening pigments in their leaves that act in the same way as sun cream. When trees begin to reabsorb these screening pigments before shedding their leaves, they expose their chloroplasts to much greater levels of UV radiation. These levels are easily high enough to destroy chlorophyll pigments and thus, stops a tree from being able to photosynthesise efficiently.

In his research, Feild found that senescing leaves produced more anthocyanins as the intensity of the UV radiation they were exposed to increased, supporting his idea that they are produced as protective screening pigments.

Feild argues that a deciduous tree counters this by investing in the production of anthocyanins, which serve as 'replacements' for the screening pigments that are reabsorbed. Thus, the presence of the red pigments allows a tree to photosynthesise for much longer than it could have ordinarily, making it much more likely to survive the winter. Furthermore, due to the relative toxicity of anthocyanins, a tree would have little incentive to reabsorb them and would have no qualms in losing the pigments when their leaves fall.

Hamilton's coevolution theory differs from Feild's hypothesis in that it considers the effects that the red colouration of foliage has, assuming that it is an honest signal to pests about a tree's defensive investment. As said above, anthocyanins are relatively toxic and are harmful to herbivorous aphids that are known to colonise trees throughout autumn. Thus, by producing more anthocyanins, which in turn makes leaves redder, a tree invests in defences that will help it to survive the winter; i.e. the more anthocyanins it produces, the less likely it is that pests can survive by living on it.

Hamilton argues that aphids have learnt to avoid trees with the brightest red foliage as they know that these will be the most difficult trees to survive on, instead colonising trees with a lower defensive commitment. Due to this active selection by aphids and other pests, producing a bright red foliage would be under a strong evolutionary pressure since such trees will be healthier in the spring and thus, will be more likely to reproduce and pass on their genes so that overtime, leaves produce more and more anthocyanins.

Hamilton noticed that the amount of anthocyanins synthesised by trees varied, evidenced by the variety of red hues that are displayed between individual trees. If the pigments were produced solely to protect against UV light, it would be expected for all of the members of a species to show the same levels of anthocyanins in their leaves, which is not the case. Furthermore, Hamilton found that the trees displaying the reddest foliage showed the lowest concentrations of aphid pests.

Both of the theories discussed above are very controversial within the scientific community at the moment and are not widely accepted. Despite this, there are many botanists and biologists that believe at least one of them to be correct, as they are unable to accept that such energetically expensive pigments as anthocyanins would be produced without a good purpose - this is not how nature works and proteins are only produced if they are needed or the resources are used to produce something else. For example, human muscle mass begins to deteriorate after about 2 weeks of inactivity as their body determines that it is not being used anymore and stops expending resources and energy to maintain it. 

Many biologists however, myself included, go even further than just believing one of these theories to be true and have noted that neither of these theories appear to contradict each other. In fact, they do not and are not mutually exclusive. Thus, it may well be that anthocyanins have a dual purpose and were originally produced by trees to extend the length of time that they could photosynthesise for and, due to their bright colour, soon developed a secondary role in deterring aphid invasion!

7 November 2012

World's most poisonous animals

The world is a cruel and unforgiving place; particularly for wild animals who spend their lives roaming the Great Outdoors. Only the best and fittest individuals are able to survive in it, which largely involves evading capture or the hunting and killing of smaller and weaker animals. Simply put, an animal must either kill or be killed if it is to carry on living. As melodramatic as this sounds, it's one of the most fundamental rules of Nature.

Due to this, animals have come up with a whole range of ingenious weapons to fight with and defences that guard against their demise. From horns to armour plating, animal evolution has been driven the effectiveness of their arsenals and no weapons are more deadly and feared that poisons - toxic chemicals that are injected via bites, stings or touch to incapacitate or kill both predators and prey alike.

Although there are thousands of different poisonous animals, there is a huge range in their toxicity and the damage that they can cause, meaning that not all poisonous animals are deadly. However, there are many that are incredibly dangerous and this post provides a comprehensive list of the most poisonous animals in the world.

10: Pufferfish

Pufferfish mainly use their poison in self defence. When they are threatened by a predator, pufferfish swallow large quantities of water and inflate their body so that their toxic spines stand on end.

Pufferfish poison produces a rapid and violent death within 24 hours of being stung, where an individual experiences heart palpitations, difficulty in breathing, muscle spasms/paralysis and vomiting. There is no known cure to their poison and victims eventually find themselves unable to breath, and die.

9: Golden dart frog

The venom of the golden dart (or poison) frog, Phyllobates terribilis, was once rubbed onto darts and arrowheads by hunters in South America to make their weapons even more deadly.

The golden dart frog is the most poisonous amphibian on Earth and excretes its toxins directly onto its skin. Due to this, it is extremely dangerous to pick up one of the frogs, and there is enough venom spread over the surface of its body to kill 20, 000 mice or 10 adult humans.

8: King cobra

The snake-eating king cobra, Ophiophagus hannah, is the world's longest venomous snake and can grow to lengths of 5.6 metres (18.5 feet).

As well as possessing a very potent poison that can kill in itself, the king cobra is the master of 'overkill' and injects huge quantities of venom with each bite. For example, it injects 5 times more poison into its victims than does the infamously violent black mamba. In fact the king cobra injects enough venom to kill an elephant within 3 hours, if it bites them in a vulnerable area such as on their trunk.

7: Brazilian wandering spider

The Brazilian wandering spider, Phoneutria nigriventer, is also called the armed spider and is extremely aggressive, living in banana plantations throughout Brazil.

The Brazilian wandering spider is the most deadly arachnid in the world and is named due its tendency to wander into peoples homes and clothing, where they hide during the day. Their bite is not only deadly and extremely painful, but can also lead to sustained and highly uncomfortable erections in men (priapisms) that often leads to long-term impotence.

6: Stonefish

Stonefish are found in the shallow waters of Eastern Australia and actually use their poison for self defence, raising their spines only when threatened rather than to hunt their prey of shrimps and small fish.

The toxins that the stonefish inject through their spines are said to be so painful that many who have been stung have said that they would rather have had their limb amputated than have endured the pain. In fact, the pain that they cause is believed to be on the threshold of human sensation, being described by many female victims as being infinitely worse than childbirth. Once stung, an adult will normally die within two hours if they do not seek immediate medical help.

5: Deathstalker scorpion

The Deathstalker scorpion, Leiurus quinquestriatus, probably has one of the most unpleasant poisons on this list. After being stung, a person will suffer from unbearable pain before falling into a deep coma. While in this coma, the scorpion's toxins destroy the person's nervous system, leading to irreversible paralysis and eventually, death.

Despite having one of the most potent venoms in nature, the Deathstalker scorpion will probably save more lives in the future than it ends. Their poison contains a unique clorotoxin that can be modified by scientists so that it attaches only to cancerous cells in the human brain, leaving healthy cells alone. Chemotherapeutic drugs can be attached the chlorotoxin before it is injected, effectively forming a 'magic bullet' drug that hunts down and destroys the cells in brain tumours.

4: Blue-ringed octopus

The blue-ringed octopus, Hapalochlaena lunulata, is tiny, being scarcely larger than a  golf ball and typically feeds off small crabs and shrimps.

Like all species of octopus, the blue-ringed octopus possess specialised skin cells that allow them to change colour depending on their mood. Oddly, their lethal and incurable bite is painless and usually contains enough venom to kill 26 adult humans.

3: Marbled cone snail

The marbled cone snail, Conus marmoreus, is a predatory snail that lives in the Indo-Pacific Ocean. Relative to its size, the snail is the most poisonous animal on the planet.

Due to the slow and cumbersome nature of snails, some of you no doubt find the whole idea of a predatory snail as being unlikely. It would seem that you are not alone in this and the snails appear to have noticed their limitations in speed and manoeuvrability as well, actually hunting via a poisonous 'harpoon' that they launch at fish that get too close. This harpoon is absolutely lethal, being loaded with enough poison to kill 20 adult humans.

2: Inland taipan

Also called the small-scaled snake and the fierce snake, the inland taipan, Oxyuranus microlepidotus, is native to Australia and is the most venomous snake in the world; with its poison being able to kill an adult human within 45 minutes after being bitten.

An adult inland taipan is thought to have enough venom in its body at any one time to kill 250, 000 mice or 100 humans! Unbelievably, its nervous system attacking venom has been calculated to be 50 times more deadly than the common cobra and 10 times as toxic as the Mojave rattlesnake.

Fortunately for us, the inland taipan is an exceedingly shy snake that rarely bites unless it has been provoked;  and even then, bites are rare. Due to this docile nature, no human deaths* have ever been recorded.

1: Box jellyfish

There are several different species of box jellyfish spread throughout many tropical and subtropical oceans, which all contain extremely damaging toxins, and can be easily distinguished by their cube-shaped 'heads'.

Sadly, box jellyfish have been responsible for more than 5, 500 recorded deaths since 1954*. Their poison is highly potent and attacks their victim's heart, skin and nervous tissue. If stung by a box jellyfish, a person has little chance of survival unless they receive medical help almost immediately. Fortunately, the acetic acid found in vinegar can counteract some of the effects of the poison and stop any undischarged nematocysts from injecting more venom into the wound caused by their tentacles.

Despite its incredibly potent venom and the vast number of deaths box jellyfish have caused, it is worth noting that some scientists argue that they not actually the most poisonous animal in the world and that the highly esteemed honour should be awarded to its closely related cousin, the tiny Irukandji jellyfish.

* to the best of my knowledge, the figure was correct at the time this article was published.

4 November 2012

Lyes of attraction

Except for the occasional white lie here and there, most of us try to avoid deceiving our families and friends and dislike being lied to by others. Lying is not considered a positive trait and people who tell fibs too often are mistrusted and usually find that they have fewer friends than they thought they did.

As you undoubtedly know, lying is a particularly huge issue in relationships and has probably broken up more couples over human history than we can record. This comes as no surprise and dumped liars rarely receive sympathy as we all know that it's their own fault. What is odd though, is that not all animals share our views on lying and for one species in particular, the Australian lyrebird, the better an individual can lie the more popular they are!

Lyrebirds are among the most esteemed of Australia's native animals and are famous for their impressive prowess of 'lying'.  There are just 2 species of lyrebird: the superb lyrebird (Menura novaehollandiae) that is pictured above and Albert's lyrebird (Menura alberti), which belong to their own unique genus.

In fact, being able to lie well is much more important than simply for making an individual popular - it is an essential skill that a male bird must master if he wants to attract a mate! Lyrebirds, you see, have one of the most sophisticated courtship rituals in nature, which involves splaying their luxurious tail feathers (in much the same way as a peacock), and mimicking as many noises as they possibly can. These sounds, which can be imitations of anything, such as other bird calls, car alarms and even chainsaws felling trees, are then incorporated into an elaborate song that the male may sing for up to 4 hours a day during breeding season (June to August)!

It appears that the more complex the courtship song, the more successful the male bird is in attracting a mate. Once a male lyrebird has successfully mated with a female bird, she lays a single egg in a nest that she's made on the ground, and incubates it as the sole parent for nearly 2 months.

Analysis of the songs made by courting lyrebirds has found that they are usually split into 7 clearly distinct sections, where about 80% of the entire song is made from mimicry. Male and female lyrebirds both become sexually mature before they are 10 years old, although it should be noted that females mature a few years earlier than males do. Due to this, male birds don't actually start singing properly until they are almost a decade old. Before then, males are believed to practise 'lying' where they learn to modulate their highly developed voice box so that it can mimic almost any sound they hear.

Thus, the ability to lie and produce a whole host of sounds that are not normally made by lyrebirds is a huge part of their culture and has made the passerine (song) birds one of the most noted birds in Australia, and maybe even in the world.