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Archive for September, 2009
Bdelloid rotifers – 80 million years without sex
This article is reposted from the old WordPress incarnation of Not Exactly Rocket Science. The blog is on holiday until the start of October, when I’ll return with fresh material.
Sex is, on the whole, a good thing. I know it, you know it, and natural selection knows it. But try telling it to bdelloid rotifers. These small invertebrates have survived without sex for some 80 million years.
While many animals, from aphids to Komodo dragons, can reproduce asexually from time to time, it’s incredibly rare to find a group that have abandoned sex altogether. The bdelloid rotifers (pronounced with a silent b) are an exception.
They live in an all-female world and since their discovery, not a single male has ever been found. Genetic studies have confirmed that they are permanently asexual, and females reproduce by spawning clone daughters that are genetically identical to them.
The bdelloids pose a problem for evolutionary biologists, who have struggled to explain how they could make do without a strategy that serves the rest of the animal kingdom very well. Now, Natalia Pouchkina-Stantcheva, Alan Tunnacliffe and colleagues from the University of Cambridge have found out how they do it.
Sexual animals have two copies of each gene that have only minimal differences between them. But the asexual bdelloid lifestyle has uncoupled the fates of each copy in a gene pair, allowing them to evolve in new directions. They get two genes for the price of one.
One of the vaunted benefits of sex is that it acts as a crucible for genetic diversity. Animals receive one pair of every gene from their mother and one from their father. As the pairs are united in the embryo, they are often shuffled into new combinations.
The evolution of the past tense – how verbs change over time
This article is reposted from the old WordPress incarnation of Not Exactly Rocket Science. The blog is on holiday until the start of October, when I’ll return with fresh material.
For decades, scientists have realised that languages evolve in strikingly similar ways to genes and living things. Their words and grammars change and mutate over time, and new versions slowly rise to dominance while other face extinction.
In this evolutionary analogy, old texts like the Canterbury Tales are the English language’s version of the fossil record. They preserve the existence of words that used to be commonplace before they lost a linguistic Darwinian conflict with other, more popular forms.
Now, Erez Lieberman, Martin Nowak and colleagues from Harvard University are looking at this record to mathematically model how our verbs evolved and how they will change in the future.
Today, the majority of English verbs take the suffix ‘-ed’ in their past tense versions. Sitting alongside these regular verbs like ‘talked’ or ‘typed’ are irregular ones that obey more antiquated rules (like ‘sang/sung’ or ‘drank/drunk’) or obey no rules at all (like ‘went’ and ‘had’).
In the Old English of Beowulf, seven different rules competed for governance of English verbs, and only about 75% followed the “-ed” rule. As the centuries ticked by, the irregular verbs became fewer and far between. With new additions to the lexicon taking on the standard regular form (‘googled’ and ‘emailed’), the irregulars face massive pressure to regularise and conform.
Today, less than 3% of verbs are irregular but they wield a disproportionate power. The ten most commonly used English verbs – be, have, do, go say, can, will, see, take and get – are all irregular. Lieberman found that this is because irregular verbs are weeded out much more slowly if they are commonly used.
How India became the fastest continent
This article is reposted from the old WordPress incarnation of Not Exactly Rocket Science. The blog is on holiday until the start of October, when I’ll return with fresh material.
You don’t normally hear continents described as speedy, but it’s now clear that some are much faster than others. India, in particular, is the Ferrari of continents and now, scientists have discovered why.
Rewind 150 million years and the Earth looked very different. Most of the land in today’s southern hemisphere were united in a single super-continent called Gondwana, including Africa, Australia, South America, Antarctica, India and Arabia.
The Earth’s crust is not a stationary shell but an ever-shifting mosaic of tectonic plates that constantly (albeit slowly) reshape the face of the planet. Underneath the crust lies the much hotter mantle, and plumes of super-heated rock occasionally erupt out of this layer, causing hotspots of volcanic activity.
Geologists believe that a particularly large ‘mantle plume’ kick-started the break-up of Gondwana. Now, Prakash Kumar and colleagues from the National Geophysical Research Institute in India have found that the plume also gave India a turbo boost.
Elephants smell the difference between human ethnic groups
This article is reposted from the old WordPress incarnation of Not Exactly Rocket Science. The blog is on holiday until the start of October, when I’ll return with fresh material.
It’s tempting to think that elephants have their own PR agency. Just last week, their mighty reputation was damaged by the revelation that they are scared away by bees but they have bounced back with a new study that cements their standing among the most intelligent of animals.
Lucy Bates and colleagues from the University of St Andrews have found that African elephants (Loxodonta africana) can tell the difference between different human ethnic groups by smell alone. They also react appropriately to the level of threat they pose.
The Massai, for example, are a group of cattle-herders, whose young men sometimes prove themselves by spearing elephants. Clearly, it would pay to be able to sort out these humans from those who post little threat, like the Kamba.
At the Amboseli National Park in Kenya, Bates found that elephants reacted more fearfully to clothes previously worn by a Massai man than to clean ones or those worn by a Kamba man. She placed the three types of cloth near 18 family groups and watched what happened.
When the first individual caught whiff of a new scent, it raised its head and curled its trunk towards the source of the smell. If they smelled Massai clothes, they moved away particularly fast, travelled about five times further and took more than twice as long to relax. They could clearly tell the difference between the two groups based on smell and reacted more defensively to the dangerous one.
Every single time the elephants smelled Massai on the wind, they moved downwind and didn’t stop until they reached tall elephant grass, over 1m in height. They only sought tall grass in about half of the trials with Kamba clothes, and almost none of the trials with clean clothes. To Bates, this was a clear sign of planned action for elephant grass only covers about 7% of Amboseli.
Ants herd aphids with tranquilisers in their footsteps
This article is reposted from the old WordPress incarnation of Not Exactly Rocket Science. The blog is on holiday until the start of October, when I’ll return with fresh material.
In your garden, there’s a fair chance that a farmer is currently tranquilising her livestock with a chemical cocktail she secretes from her feet. Don’t believe me? Look closer…
Humans aren’t the only species that farms other animals for food – ants do it too and their herds consist of aphids. They feed on plant sap and excrete a sweet and nutritious liquid called honeydew, which the ants drink.
In return, the ants run a protection racket, defending the aphids from predators like ladybirds. It seems like a nice two-way partnership that suits both partners, and aphid colonies tended by ants tend to be larger than unattended ones. But new research from two London universities suggests that ants are manipulating their herds more than previously thought.
Aphid-farming ants similar problem to human farmers – their herds are likely to wander away and it’s in the ants’ interests to prevent this. Earlier work showed that they sometimes bite the wings off aphids that have them or produce chemicals from glands in their jaws that subdue the development of wings in the first place.
None of that stops the several wingless individuals from just walking away, so the ants use another trick. Thomas Oliver from Imperial College London found that the black garden ant (Lasius niger) secretes chemicals in its footsteps that effectively tranquilise aphids.
Buzzing bees scare elephants away
This article is reposted from the old WordPress incarnation of Not Exactly Rocket Science. The blog is on holiday until the start of October, when I’ll return with fresh material.
It’s a myth that elephants are afraid of mice, but new research shows that they’re not too keen on bees. Even though they fearlessly stand up to lions, the mere buzzing of bees is enough to send a herd of elephants running off. Armed with this knowledge, African farmers may soon be able to use strategically placed hives or recordings to minimise conflicts with elephants.
Iain Douglas-Hamilton and Fritz Vollrath from Kenyan conservation charity Save the Elephants first suspected this elephantine phobia in 2002, when they noticed that elephants were less likely to damage acacia trees that contained beehives.
Animals as powerful as the African elephant can go largely untroubled by predators. Their bulk alone protects them from all but the most ambitious of lion prides.
But these defences do nothing against the African bees, which can sting them in their eyes, behind their ears and inside their trunks. Against these aggressive insects, the elephants are well justified in their caution and local people have reported swarms of bees chasing elephants for long distances.
Lucy King, a graduate student from the University of Oxford confirmed this theory by using camouflaged wireless speakers to play recordings of angry buzzing bees to herds of elephants resting under trees.
Ancient plants manipulate insects for hot, smelly sex
This article is reposted from the old WordPress incarnation of Not Exactly Rocket Science. The blog is on holiday until the start of October, when I’ll return with fresh material.
For plants too, sex can be a hot and smelly affair. In most plant-insect partnerships, the pollinator seems to do most of the work by voluntarily transferring pollen from plant to plant in exchange for a meal.
But an ancient lineage of plants – the cycads – takes more active steps to ensure its future with a bizarre combination of heat and smells. In the afternoon, they use heat and a toxic stench to drive insects out of male cones only to lure them into female cones in the evening with a more alluring scent.
Cycads were around before the time of the dinosaurs and their six-legged puppets are a group of similarly ancient insects called thrips. The thrips make their homes among the single large cone that sits atop the cycad trunk, looking like an enormous pine cone.
The thrips prefer the male ones, for their cracks are laden with nutritious pollen that the insects and their larvae eat. But their lodgings aren’t free. Irene Terry and colleagues from the University of Utah found that the cycads manipulate them into earning their keep.
When the time comes to pollinate, the cycad cones heat up. By rapidly metabolising stores of fats, sugars and starches, they can raise the temperature of the cones to 12C above the surrounding temperature, up to about 37C.
Doctors repress their responses to their patients' pain
This article is reposted from the old WordPress incarnation of Not Exactly Rocket Science. The blog is on holiday until the start of October, when I’ll return with fresh material.
Many patients would like their doctors to be more sensitive to their needs. That may be a reasonable request but at a neurological level, we should be glad of a certain amount of detachment.
Humans are programmed, quite literally, to feel each others’ pain. The neural circuit in our brains that registers pain also fires when we see someone else getting hurt; it’s why we automatically wince.
This empathy makes evolutionary sense – it teaches us to avoid potential dangers that our peers have helpfully pointed out to us. But it can be liability for people like doctors, who see pain on a daily basis and are sometimes forced to inflict it in order to help their patients.
Clearly, not all doctors are wincing wrecks, so they must develop some means of keeping this automatic response at bay. That’s exactly what Yawei Chang from Taipei City Hospital and Jean Decety from University of Chicago found when they compared the brains of 14 acupuncturists with at least 2 years of experience to control group of 14 people with none at all.
They scanned the participants’ brains while they watched videos of people being pricked by needles in their mouths, hands and feet, or being prodded with harmless cotton swabs. Sure enough, the two groups showed very different patterns of brain activity when they watched the needle videos, but not the cotton swab ones.
Genes affect our likelihood to punish unfair play
This article is reposted from the old WordPress incarnation of Not Exactly Rocket Science. The blog is on holiday until the start of October, when I’ll return with fresh material.
As a species, we value fair play. We’re like it so much that we’re willing to eschew material gains in order to punish cheaters who behave unjustly. Psychological games have set these maxims in stone, but new research shows us that this sense of justice is, to a large extent, influenced by our genes.
When it comes to demonstating our innate preference for fair play, psychologists turn to the ‘Ultimatum Game‘, where two players bargain over a pot of money. The ‘proposer’ suggests how the money should be divided and the ‘receiver’ can accept of refuse the deal. If they refuse, neither player gets anything and there is no room for negotiation. In a completely rational setting, the proposer should offer the receiver as little as possible, and the receiver should take it – after all, a very little money is better than none at all.
Of course, that’s not what happens. Receivers typically abhor unfair offers and would rather that both parties receive no money than accept a patronisingly tiny amount. Across most Western countries, proposers usually offer the receivers something between 40% and 50% of the takings. Any offers under 10% are almost always rejected.
The uniformity of responses across Western countries suggests that culture has a strong effect on how people play the game, but until now, no one had looked to see how strongly genes asserted their influence. Bjorn Wallace and colleagues from the Stockholm School of Economics decided to do just that, and they used the classic experiment for working out heritability – the twin study.
Sabre-toothed cats had weak bites
This article is reposted from the old WordPress incarnation of Not Exactly Rocket Science. The blog is on holiday until the start of October, when I’ll return with fresh material.
The sabre-toothed cat is one of the most famous prehistoric animals and there is no question that it was a formidable predator, capable of bringing down large prey like giant bison, horses, and possibly even mammoths. The two massive canines – the largest teeth of any mammal – are a powerful visual. But while they were clearly powerful weapons, scientists have debated their use for over 150 years.
Now, a new study shows that Smilodon, the most iconic of the sabre-tooths, had a surprisingly weak bite. They were a precision weapon that were used to deliver a single, final wound to an already subdued victim – the equivalent of an assasin’s stiletto rather than a swordsman’s blade.
Earlier suggestions pictured Smilodon using its teeth to hang onto the back of large prey, to slash their abdomens open, or to impale them at the end of a flying pouce. One of the most popular theories said that the cat would have used its teeth to sever arteries and airways with a decisive bite to the throat – a quicker technique than the suffocating neck bites used by modern lions.
Working out how strongly Smilodon could bite would go a long way towards deciding on one of these theories and to do that, palaeontologists have studied the animal’s fossilised skull. Even then, opinions have gone either way depending on which bit of the skull they looked at. The muscle attachment points suggest it has small jaw muscles, but the bite could have been powered from the neck. The lower jaw is smaller, but strongly built, lending weight to the idea of a powerful bite.
To get some clearer answes, Colin McHenry and colleagues from the University of Newcastle, Australia decided to put Smilodon‘s skull through a digital crash-test. They used a technique called ‘finite element analysis‘ or FEA, which is typically used in mechanical engineering and crash-testing for cars.
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