Archive for July, 2009

Foul-tasting ant parasitises the colonies of other species

By Ed Yong | July 31, 2009 9:40 am

This article is reposted from the old WordPress incarnation of Not Exactly Rocket Science.

Blogging on Peer-Reviewed ResearchAn ant nest is sheltered, well defended and stocked with food, but one that takes time to build and protect. That’s why some species of ants don’t bother to do it themselves – they just squat in the nests of others.

Formicoxenus nitidulus escapes its hosts' larger jaws by tasting foul.These ants are ‘social parasites’ – they don’t feed off their hosts’ tissues, but instead steal their food, sleep in their homes and use their resources. They’re like six-legged cuckoos

An ant colony is too dangerous a target to victimise lightly and the social parasites use several tricks to stop their hosts from ripping them apart. Some escape reprisal by chemically camouflaging themselves, either by mimicking their hosts’ odour, or by acquiring it through contact.

This specialised strategy ties the parasite’s fates into those of its host. Both are caught in an evolutionary arms race, with the hosts becoming more discriminating and the parasites’ deception becoming more accurate. But Stephen Martin from the University of Sheffield has found one ant species with a completely different and more flexible strategy – it tastes really, really bad.

Ants of the genus Formicoxenus raise their young in the colonies of other ants. Some species have earned the nickname of ‘shampoo ants’ for their tendency to spend almost half their time licking their hosts. As they do so, they acquire the hosts’ odour and blend into the colony, escaping discovery and reprisals.

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An entire bacterial genome discovered inside that of a fruit fly

By Ed Yong | July 30, 2009 12:00 pm

This article is reposted from the old WordPress incarnation of Not Exactly Rocket Science.

Blogging on Peer-Reviewed ResearchA humble species of fruit fly is the genetic equivalent of a Russian doll – peer inside its DNA and you will see the entire genome of a species of bacteria hidden within.

Wolbachia in yellow infecting insect cells in red.The bacteria in question is Wolbachia, the most successful parasite on earth and infects about 20% of the world’s species of insects. It’s a poster child for selfishness. To further its own dynasty, it has evolved a series of remarkable techniques for ensuring that it gets passed on from host to host. Sometimes it gives infected individuals the ability to reproduce asexually; at other times, it does away with an entire gender.

Now, Julie Dunning-Hotopp from the J. Craig Venter Institute and Michael Clark from the University of Rochester have found an even more drastic strategy used by Wolbachia to preserve its own immortality – inserting its entire genome wholesale into that of another living thing.

Among bacteria, such gene swaps are run-of-the-mill. Humans and other multi-celled creatures must (mostly) contend ourselves with passing our genes to our young but bacteria have no such limits. They can exchange genes as easily as we exchange emails and this free trade in DNA, formally known as ‘horizontal gene transfer’, allows them to swap beneficial adaptations such as drug resistance genes.

Gene transfer between bacteria and eukaryotes is rare but if any bacteria was well placed to do it, it would be Wolbachia. It infects the developing sex cells of its hosts and gets passed on from mother to child in the egg itself – a prime location for integrating its genes into those of the next generation.

Drosophila ananassae has a stowaway in its genome.Other labs had already managed to detect traces of Wolbachia genes in a species of beetle and a nematode worm. To discover the full extent of its genetic infiltration, Dunning-Hotopp and Clark decided to search for Wolbachia genes in a wide range of invertebrates.

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Fruit flies have a taste for fizzy drinks

By Ed Yong | July 29, 2009 12:00 pm

This article is reposted from the old WordPress incarnation of Not Exactly Rocket Science.

Blogging on Peer-Reviewed ResearchFizzy drinks like Perrier and Coca-Cola are targeted at a huge range of social groups, but if fruit flies had any capital to spend, they’d be at the top of the list. Unlike posh diners or hyperactive kids, flies have taste sensors that are specially tuned to the flavour of carbonated water.

Humans can pick up five basic tastes – sweet, salty, sour, bitter and umami (savoury). But other animals, with very different diets, can probably expand on this set. And what better place to start looking for these unusual senses than the fruit fly Drosophila, a firm favourite of geneticists worldwide, and an animal with very different taste in food to our own.

Drosophila‘s tongue contains structures that are the equivalent of our own taste buds. They are loaded with taste-sensitive neurons and the activity of specific genes gives these neurons the ability to recognise different tastes.

Other researchers have already isolated the genes that allow Drosophila to tell sweet from bitter. But when Walter Fischler found a group of taste cells that didn’t have either of these genes and connected to a different part of the fly’s brain, he knew he was on to something new.

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A brief hiatus

By Ed Yong | July 28, 2009 7:03 pm

Folks,
I’m taking a bit of a breather from blogging for a week. My wife and I are celebrating our second-year anniversary and I’m lavishing her with attention for a week. It’s also a busy time at my day job, and it’s a slow news week – a fortuitous confluence of events which mean that I get to put my feet up for a bit.
I’ll be back with fresh material probably on Sunday. Until then, I’ll be posting up some oldies (but goodies) from the WordPress site.
E

CATEGORIZED UNDER: Personal

Virtual reality illusions produce out-of-body experiences in the lab

By Ed Yong | July 28, 2009 10:30 am

This article is reposted from the old WordPress incarnation of Not Exactly Rocket Science. 

Blogging on Peer-Reviewed ResearchThe idea of an out-of-body experiences seems strange and hokey – certainly not one that would grace one of the world’s top scientific journals. So it may seem surprising that two years ago, Science published not one, but two papers that considered the subject through the lens of scientific scrutiny.

Out-of-body experiences are rooted in malfunctioning brain mechanismsOut-of-body experiences are rare and can be caused by epileptic fits, neurological conditions such as strokes and heavy drug abuse. Clearly, they are triggered when something goes wrong in our brains. And as usual for the brain, something going wrong can tell us a lot about what happens the rest of the time.

Simply put, if we very rarely have an out-of-body experience, why is it that for the most part we have ‘in-body’ experiences? It’s such a fundamental part of our lives that we often take it for granted, but there must be some mental process that ensures that our perceptions of ‘self’ are confined to our own bodies. What is it?

Two groups of scientists have taken steps to answering these questions using illusion and deception. They managed to experimentally induce mild out-of-body experiences in healthy volunteers, by using virtual reality headsets to fool people into projecting themselves into a virtual body.

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Noise pollution drives away some birds, but benefits those that stay behind

By Ed Yong | July 27, 2009 8:30 am

Blogging on Peer-Reviewed ResearchCities are noisy places. If you ever get annoyed by the constant din of traffic, machinery and increasingly belligerent inhabitants, think about what songbirds must think. Many birds rely on songs to demarcate their territories and make their advances known to mates. They listen out not just for the sounds of seduction or rivalry, but for approaching predators and alarm calls that signify danger. Hearing these vital notes may be the different between life and death.

Last year, I wrote a feature for New Scientist about the effect that urban noise has on songbirds. Those that can’t make themselves heard are being pushed out of cities; others have developed strategies to rise above the clamour. British robins have avoided the traditional dawn chorus, when rush hour is at its peak, in favour of night-time singing when their tunes can stand out. German nightingales take the more straightforward approach of singing very loudly, belting out their songs at 95 decibels, enough to damage human hearing if sustained. And some species – great tits, house finches and blackbirds – have opted for higher notes, which are less easily masked by the typically low frequencies of urban noise.

So some species are adaptable enough to thrive in a cacophonous environment that would drive out those that can’t change their tune. And if the species that are driven away include predators and thieves, the birds that remain fare even better. That scenario is playing out in the cities of America. Clinton Francis from the University of Colorado at Boulder has found that noise reduces the diversity of bird communities but it actually helps those that remain.

Previous studies have linked the presence of noisy roads and industries with sparser populations of local birds,  but never conclusively. Noise is also associated with habitat changes or visual disturbances, and it makes it harder for scientists themselves to spot birds – all of these factors could explain any disappearances.

To get around these problems, Francis relied on a unique natural experiment, taking place in the woodlands of New Mexico. Here, natural gas is pumped out of the ground and at some sites, it is then pushed along pipelines by compressors that are very noisy and that operate constantly. Other sites that lack compressors are much quieter but essentially the same in terms of environment and the surrounding trees. By comparing woods near noisy and quieter gas wells, Francis could isolate the effects of noise from those of the mere presence of industry. He even managed to get the compressors turned off for short windows while his team took stock of the local birdlife.

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CATEGORIZED UNDER: Animals, Birds, Conservation, Ecology
MORE ABOUT: bird, noise pollution, urban

Snails get sexy when parasites are around

By Ed Yong | July 24, 2009 10:00 am

Blogging on Peer-Reviewed ResearchIn Lake Alexandrina, New Zealand, a population of snails is under threat from a parasitic flatworm, a fluke aptly known as Microphallus. The fluke chemically castrates its snail host and uses its body as a living incubator for its larvae. But the snails have a weapon against these body-snatching foes – sex.

The New Zealand mud snail Potamopyrgus antipodarum is found throughout island’s freshwater habitats. They breed either sexually or asexually through cloning, and the two strategies vary in prevalence throughout the lake. In the shallower waters round its margins, sex is the name of the game, but in the deeper waters towards the lake’s centre, snails are more likely to opt for cloning.

Kayla King from Indiana University has shown that it’s the concentration of the local parasites that drives this gradient of sex. The flukes spend their adult lives in ducks and they rely on the birds inadvertently scooping up their larvae while feeding. In Lake Alexandrina, ducks only feed in the shallow waters around the lake’s margins so these areas are hotspots for parasites, and for co-evolutionary wars between them and their snail hosts. Sex provides the snails with the genetic ammunition they need to stay in the game.

The snails and their parasites beautifully support and illustrate the principles of the Red Queen hypothesis, which suggests that one of the chief benefits of sex lies in providing the genetic innovation necessary to outfox parasites in evolutionary arms races.

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Toucan play at reducing the heating bill

By Ed Yong | July 23, 2009 1:00 pm

Blogging on Peer-Reviewed ResearchRelative to its body size, the huge beak of the toco toucan is the largest of any bird. It allows the toucan to eat both fruit and small animals, and display to both mates and rivals. Darwin himself speculated that it acts as a billboard, shaped by sexual selection to display bright colours that could be attractive to potential mates. But the toucan’s bill has another function that has only been discovered. Like the ears of an elephant, the toucan’s bill is a radiator.

It certainly has all the characteristics of a biological radiator. It’s big and has a surface area that’s 25-40 times larger than normal for a bird of its size; in fact, the bill accounts for 30-50% of the bird’s total surface area. It also lacks any insulating layer of fat, feathers or fur, and beneath its horny exterior, lies a rich network of blood vessels.

These vessels are the means through which the toucan exchanges heat. When it’s warm, it widens the vessels and allows the heat of its blood to radiate into the atmosphere. When it’s too cold, it limits the loss of heat by shutting down the blood flow to its bill.

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CATEGORIZED UNDER: Animal behaviour, Animals, Birds

Your brain on Oprah and Saddam (and what that says about Halle Berry and your grandmother)

By Ed Yong | July 23, 2009 11:00 am

Blogging on Peer-Reviewed ResearchFrom the scientists who brought you the infamous ‘Halle Berry neuron’ and the ‘Jennifer Aniston neuron’ come the ‘Oprah Winfrey neuron’ and the ‘Saddam Hussein neuron’.

Four years ago, Rodrigo Quian Quiroga from Leicester University showed that single neurons in the brain react selectively to the faces of specific people, including celebrities like Halle Berry, Jennifer Aniston and Bill Clinton. Now, he’s back, describing single neurons that respond selectively to the concept of Saddam Hussein or Oprah Winfrey. This time, Quiroga has found that these neurons work across different senses, firing to images of Oprah or Saddam as well as their written and spoken names.

In one of his volunteers, Quiroga even found a neuron that selectively responded to photos of himself! Before the study began, he had never met the volunteers in the study, which shows that these representations form very quickly, at least within a day or so.

In his original experiments, Quiroga used electrodes to study the activity of individual neurons, in the brains of patients undergoing surgery for epilepsy. As the volunteers saw photos of celebrities, animals and other objects, some of their neurons seemed to be unusually selective. One responded to several different photos of Halle Berry (even when she was wearing a Catwoman mask), as well as a drawing of her, or her name in print. Other neurons responded in similarly specific ways to Jennifer Aniston or to landmarks like the Leaning Tower of Pisa.

The results were surprising, not least because they seemed to support the “grandmother cell theory“, a paradox proposed by biologist Jerry Lettvin. As Jake Young (now at Neurotopia) beautifully explains, Lettvin was trying to argue against oversimplifying the way the brain stores information. Lettvin illustrated the pitfalls of doing so with a hypothetical neuron – the grandmother cell – that represents your grandmother and is only active when you think or see her. He ridiculed that if such cells existed, the brain would not only run out of neurons, but losing individual cells would be catastrophic (at least for your poor forgotten grandmother).

The grandmother cell concept was espoused by headlines like “One face, one neuron” from Scientific American, but these read too much in Quiroga’s work. It certainly seemed like one particular neuron was responding to the concept of Halle Berry. But there was nothing in Quiroga’s research to show that this cell was the only one to respond to Halle Berry, nor that Halle Berry was the only thing that activated the cell. As Jake Young wrote, “The purpose of the neuron is not to encode Halle Berry.”

Instead, our brains encode objects through patterns of activity, distributed over a group of neurons, which allows our large but finite set of brain cells to cope with significantly more concepts. The solution to Lettvin’s paradox is that the job of encoding specific objects falls not to single neurons, but to groups of them.

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Pacman-like game shows how the best-laid plans give way to instinct as danger approaches

By Ed Yong | July 22, 2009 9:00 am

This is a repost from the old WordPress incarnation of Not Exactly Rocket Science

Blogging on Peer-Reviewed ResearchYou are being hunted, chased through a labyrinth by a relentless predator. Do you consider your options and plan the best possible escape, or do you switch off and rely solely on instinct? A new study provides the answer – you do both, flicking from one to the other depending on how far away the threat is.

When predators close in, instinct takes over.Earlier studies have found that different parts of a rodent’s brain are activated in the face of danger, depending on how imminent that danger is. Now, scientists at University College London has found the same thing in human brains.

It would be a poor strategy to stick to the same defensive behaviours in all situations. Simply put, there are threats and there are threats, and we need different kinds of behaviour to cope with different scales of danger. When a predator is fifty feet away, we have the time and space to consider our options and plan an escape. But when it’s five feet away, such luxuries are ill-afforded and behaviour needs to be fast and reflexive. In the millisecond between life and death, the best laid plans of mice and men take a back seat in the light of three simple options – fight, flight or freeze.

This sounds fairly obvious, but Dean Mobbs and colleagues actually watched the switch taking place by scanning the brains of several volunteers as they were being chased by a predator. Of course, ethics committees would frown on letting a bear loose on some volunteers, so the experiment was done in a virtual Pacman-like game, where people had to flee a virtual predator through a maze. But they weren’t completely let off the hook; if they were caught, they received an electric shock.

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