May 13, 2008
Category: Animal behaviour • Animals • Mammals
Three-toed sloths have a reputation for being some of the sleepiest of all animals, largely due to a single study, which found that captive sloths snooze for 16 hours a day. That certainly seems like a sweet deal to me, but it seems that the sloth's somnolent reputation has been exaggerated.
A new study - the first ever to record brain activity in a wild sleeping animal - reveals that wild sloths are far less lethargic than their captive cousins. In their natural habitat, three-toed sloths sleep for only 9.6 hours a day, not much more than an average first-year university student.
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Posted by Ed Yong at 7:00 PM • 0 Comments • 0 TrackBacks
May 12, 2008
Category: Insects • Mimicry • Plants
A common wasp on a foraging mission catches an enticing scent on the breeze. It's a set of chemicals given off by plants that are besieged by hungry insects and it means that there is food nearby for the wasp's grubs - caterpillars. The wasp tracks the smell to its source - a flower - and while it finds nectar, there are no caterpillars and it leaves empty-mandibled. The smell was a trick, used to dupe the wasp into becoming a unwitting pollinator for the broad-leaved helleborine.
The broad-leaved helleborine (Epipactis helleborine) is an orchid that grows throughout Europe and Asia. It is but one deceiver in a family that is rife with them. About 10,000 species of orchids trick pollinators into visiting their flowers. Some attract males by mimicking the sight and smells of females. Others resemble orchid species that provide rich nectar rewards, while providing none themselves. But while thousands of species offer the potential for sex or food, only the broad-leaved helleborine advertises itself by promising fresh meat.
Darwin himself noted that even though the helleborine packs a substantial reservoir of nectar, it is pollinated by only two species of insects - the common wasp and the European wasp. Until now, no one knew how the orchid was attracting its pollinators. Jennifer Brodmann from the University of Ulm in Germany solved the mystery by testing how wasps responded to the smells and sights of orchids.
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Posted by Ed Yong at 8:30 AM • 0 Comments • 0 TrackBacks
May 10, 2008
Category: Altruism • Cooperation • Psychology
Imagine that you're walking along a quiet street and you see a wallet lying on the pavement. Would you take it? Now imagine a slightly different situation - the wallet has a red circle drawn around it. While many people would be tempted in the first scenario, almost no one would touch the wallet in the second. The key difference is that the lone wallet was most likely dropped accidentally by a passer-by buy the encircled wallet was clearly placed and marked by someone, who may well still be watching. And there is nothing that keeps people more honest than the presence of a watchman.
Social experiments like these are of great interest to biologists because they tell us more about the nature of selfishness and altruism. In recent years, selfishness has become something of a biological buzzword and many influential writers have cast living things as self-serving vessels acting for the benefit of their genes. In this harsh light, individuals co-operate with each other only if they reap a personal reward.
But some acts of altruism, particularly human ones, are harder to explain. We are often kind and generous to others, even if they are unrelated (and so share no genes) or are unlikely to ever repay the good deed. Is this true selflessness, or is there something else going on? One theory is that such selfless acts do provide benefits - they raise the reputation of the do-gooder in the eyes of their peers. Even selfish people can act selflessly when their reputation is on the line.
Lab experiments have shown that people co-operate more strongly if they know they are being watched. But Melissa Bateson and colleagues at the University of Newcastle have shown just how honest people become when they feel that Big Brother is watching them, using a cunning experiment in a more natural environment. Rather than artificial confines of a lab, they chose to run a simple test on the unwitting members of their university's Division of Psychology in their own coffee room.
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Posted by Ed Yong at 1:00 PM • 8 Comments • 0 TrackBacks
May 9, 2008
Category: Animal behaviour • Animals • Mammals • Rats
This week's New Scientist includes a short piece from me about conformist rats. 
Until now, only humans and chimps were known to succumb to peer pressure, to the extent that we often ignore our own experiences based on the preferences of others. But a new study in brown rats shows that these rodents are similarly prone to following the Joneses. They can even be persuaded to choose a piece of food that they know makes them sick if they smell it on the breath of a 'demonstrator' rat.
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Posted by Ed Yong at 3:17 PM • 5 Comments • 0 TrackBacks
May 8, 2008
Category: Animal behaviour • Animal locomotion • Animals • Insects • Invertebrates
A tenth of the planet's population occasionally suffers through devastating famines because small insects fear being bitten in the bum. That's the astonishing message from a new study of one of mankind's greatest pests - the desert locust.
Swarms can stretch for several hundred square kilometres and each of these harbours up to 80 million hungry sets of mandibles that eat their own body weight in food every day. These plagues are unpredictable but they only form when locust populations reach some sort of critical mass. Desert locusts are two insects for the price of one; at a crowded tipping point, they transform from loners (which are green or brown) into more sociable forms that are red or yellow and prone to swarming.
With much of Asia's and Africa's food supplies at stake, researchers are keen to discover what prompts the transformation from disorders groups of solitary locusts to highly organised marches of sociable ones. Two years ago, an international team led by Stephen Simpson showed that this switch is very rapid. Once groups reach a certain density, individuals that were previously doing their own thing started stepping in line with their neighbours.
This sudden coordination is an important step in the genesis of a swarm, but the researchers had still to uncover why the locusts aligned so neatly. Now, working with the same group, Sepideh Bazazi at the University of Oxford has found part of the answer - they to march to avoid getting cannibalised by other locusts behind them. All the individuals in a dense group are after the same things - protein, salt and the like. If one stops moving, it risks acting as a source of these nutrients for others behind it. For locust groups, life is about moving with the crowd, or being eaten by it.
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Posted by Ed Yong at 12:00 PM • 3 Comments • 0 TrackBacks
May 6, 2008
Category: Animal behaviour • Animals • Birds • Mimicry
Cuckoos are some of nature's most familiar conmen. Several species of this large family are murderous slackers, who shun their own parental responsibilities by deceiving other birds into caring for their chicks. In the process, they destroy the eggs of the unwitting adopted family to ensure that their own chick gets undivided attention. But this is not the only way that cuckoos fool other birds - they also mimic hawks.
The resemblance between cuckoos and hawks (particularly sparrowhawks) has been noted for millennia. Both birds have long bodies, wings and tails and their paler, striped undersides contrast against a darker grey or brown backs. The resemblance is uncanny enough that Pliny believed that cuckoos disappeared from Europe in the winter by transforming themselves into hawks, a theory that Aristotle rightly dismissed on the grounds that cuckoos lacked the formidable talons and curved beak of hawks.
Hawks and cuckoos belong to two very different families of birds, so why do they look so similar? Non-parasitic cuckoos (and indeed, not all cuckoos leech off the parenting skills of other birds) provide an important clue, for they look much less than hawks than parasitic species. There are two possible explanations for this similarity.
The first is that both groups have independently evolved the same physical traits for the same reasons - a process called convergent evolution. Neither bird wants to be seen by potential prey or hosts. As they perch in twigs and branches, having a darker back makes them harder to spot, and bars on the underside help to break up their outline. Their body shape helps them to make a controlled glide, which sparrowhawks use to launch surprise attacks, and cuckoos use to sneak up on a targeted nest.
Alternatively, the cuckoos could be actively mimicking the hawks. The disguise could fool the cuckoos' predators. That's useful for them as they aren't particularly powerful or agile birds and they spend a lot of time on exposed perches, keeping an eye on the nests of potential victims. They could also fool potential parents. The host birds either run away, which gives the cuckoo free passage into their nests, or they mob the supposed predator en masse, which gives away the location of their precious nests. So which theory is right?
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Posted by Ed Yong at 7:01 PM • 2 Comments • 0 TrackBacks
May 5, 2008
Category: Environment • Fungi
The countryside around Iraq and the Balkans are still suffering from the ravages of wars fought in the 1990s. The environment is littered with the potentially dangerous remnants of military weapons - depleted uranium.
Depleted uranium is what's left over after 'enrichment', when uranium-235 is separated from natural uranium. This isotope is suitable for nuclear reactors and weapons, and the remainder consists of uranium-238, a less radioactive isotope with a longer half-life. This "depleted uranium" is valued by the military for its high density and is often combined with titanium to produce an alloy used in both armour-piercing weapons and defensive plating.
But penetrating rounds aren't the only potential threat to human health posed by depleted uranium. The substance is still radioactive, can cause heavy metal poisoning and burn spontaneously on impact to produce aerosols of uranium compounds. These potential risks have been downplayed by many reports but they make the use of depleted uranium in munitions highly controversial, especially when locals have to deal with traces that litter the landscape after battle ceases.
Now, a new study shows that very unlikely allies may be helping to clean up these remains. Marina Fomina from the University of Dundee found that several species of fungi can not only thrive on depleted uranium, but also convert it into stable minerals.
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Posted by Ed Yong at 7:34 PM • 8 Comments • 0 TrackBacks
May 4, 2008
Category: Genetics • Medicine & health • Obesity
This is a quick follow-up to my other post on fat cells, which as it happens, isn't the only obesity-related story out today. Another paper found a common genetic variant that increases the risk of obesity in its carriers.
A huge team of researchers scoured the genomes of almost 17,000 European people for genetic variations that are linked to obesity. Until now, only one has been found and it sits within a gene called FTO. This new study confirmed that FTO variants have the strongest association with obesity, but in the runner-up position is another variant near a gene called melanocortin-4 receptor or MC4R.
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Posted by Ed Yong at 1:15 PM • 1 Comments • 0 TrackBacks
Category: Medicine & health • Obesity
As fat people have an abundance of fat tissue, the natural assumption is that fat people have more fat cells, or 'adipocytes'. That's only part of the story - it turns out that overweight and obese people not only have a surplus of fat cells, they have larger ones too.
The idea of these 'fatter fat cells' has been around since the 1970s. But their importance has been dramatically highlighted by a new study, which shows that the number of fat cells in both thin and obese people is more or less set during childhood and adolescence. During adulthood, about 8% of fat cells die every year only to be replaced by new ones. As a result, adults have a constant number of fat cells, even those who lose masses of weight. Instead, it's changes in the volume of fat cells that causes body weight to rise and fall.
Kirsty Spalding from the Karolinska Institute in Sweden, together with a large team of international researchers, uncovered several lines of evidence to support these conclusions. Her study is a fascinating mix of cell counting, stomach surgery, radioactive Cold War fallout and a rather surprising use for carbon-dating.
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Posted by Ed Yong at 1:00 PM • 2 Comments • 0 TrackBacks
LOLbachia
