Not Exactly Rocket Science

Requests work better than orders, even when we're asking or ordering ourselves

Fri, 19 Mar 2010 08:30:31 -0500

We like to be in control of our own lives, and some of us have an automatic rebellious streak when we're told what to do. We're less likely to do a task if we're ordered to do it than if we make the choice of our own volition. It seems that this effect is so strong that it even happens when the people giving the orders are... us.

In a set of three experiments, Ibrahim Senay from the University of Illinois has shown that people do better at a simple task if ask themselves whether they'll do it than if they simply tell themselves to do so. Even a simple reversal of words - "Will I" compared to "I will" - can boost motivation and performance.

Therapists and managers alike are taught to ask people open questions that prompt them to think about problems for themselves, rather than having solutions imposed upon them. Senay's work suggests that this approach would work even if we're counselling or managing ourselves. When we question ourselves about our deeds and choices, we're more likely to consider our motivations for doing something and feel like we're in control of our actions. The effect is small but significant.

To begin with, Senay asked 53 psychology students to solve an anagram task, rearranging the letters of ten words into ten new ones. Before they started, they had to spend a minute thinking about either whether they would work on the task or simply that they would so do. The first group ended up with significantly higher scores than the second.

For his next experiment, Senay duplicated the same effect without any explicit instructions. Under the guise of a handwriting study, he asked 50 students to practice writing the words "I will", "Will I", "I", or "Will". After 20 repetitions, they were given some anagrams to do. The students who wrote "Will I" solved twice as many as those in the other groups. None of them guessed the true purpose of the experiment.

Finally, Senay asked 56 students to once again write 20 lines of either "I will" or "Will I". Afterwards, they had to rate their intentions to start exercising regularly or continue doing so. They also had to rate 12 reasons for exercising according to their relevance to them, from internal motivators like taking responsibility for their health to external motivators like feeling guilty or ashamed of being idle. As before, the simple word swap had a significant effect. The recruits who wrote "Will I" were more likely to want to exercise, and their extra impetus was driven by a boost of self-motivation rather than a stronger pull from outside influences.

This isn't the only study to show that subtle grammatical shifts can sway our intentions and behaviour. Just last year, William Hart and Dolores Albarracın (who also worked on Senay's study) showed that people are more likely to repeat their actions if they describe things they did in the imperfect tense ("I was solving anagrams") than the perfect tense ("I solved anagrams"). The latter construction firmly suggests that something was completed, while the former has more of an ongoing vibe.

This area is ripe for more investigation. Next, Senay wants to see if other verbs, like can, should or would, can affect our behaviour in a similar way. He's also interested in whether speaking in an active or passive voice matters - the answers to that question should be of interest to all scientists and science writers, especially in light of this excellent Nature piece on whether a constant use of the passive voice could be young harming scientists.

For now, Senay's work is a testament not just to the subtle power of grammar, but to the value of introspection and the simple act of asking yourself questions.

Reference: Psychological Science http://dx.doi.org/10.1177/0956797610364751 If this link isn't working, read why here

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Sperm war - the sperm of ants and bees do battle inside the queens

Thu, 18 Mar 2010 14:00:28 -0500

One night of passion and you're filled with a lifetime full of sperm with no need to ever mate again. As sex lives go, it doesn't sound very appealing, but it's what many ants, bees, wasps and termites experience. The queens of these social insects mate in a single "nuptial flight" that lasts for a few hours or days. They store the sperm from their suitors and use it to slowly fertilise their eggs over the rest of their lives. Males have this one and only shot at joining the Mile High Club and they compete fiercely for their chance to inseminate the queen. But even for the victors, the war isn't over. Inside the queen's body, their sperm continue the battle.

If the queen mates with several males during her maiden flight, the sperm of each individual find themselves swimming among competitors, and that can't be tolerated. Susanne den Boer from the University of Copenhagen has found that these insects have evolved seminal fluids that can incapacitate the sperm of rivals while leaving their own guys unharmed. And in some species, like leafcutter ants, the queen steps into the fray herself, secreting chemicals that pacify the warring sperm and ease their competition.

The amazing thing about this chemical warfare is that it has evolved independently several times. Social insects evolved from ancestors that observed strictly monogamous relationships. Even now, the queens from many species mate with just one male during their entire lives. With just one set of sperm in their bodies, they have no problem with sperm conflict. The trouble starts when species start mating with several males during their nuptial flights, as honeybees, social wasps, leafcutter ants, army ants, and others do today.

To understand the sperm wars, den Boer exposed sperm from different species to their own seminal fluids, those of brothers, or those of unrelated males. In two species of bees and three species of ants, she found that a male's seminal secretions are a boon to his own sperm. Even at small concentrations, they managed to boost the survival of sperm that had been stored in saline.

In species where queens mate with a single male, like bumblebees and Trachymyrmex zeteki ants, the seminal fluids had the same beneficial effect on the sperm of unrelated individuals. But these chemicals weren't so benign in species where queens store sperm from several males, like honeybees and the ants Atta coloimbica and Acromyrmex echinatior. There, they significantly reduced the survival rates of competitor sperm, slashing them from 6-18% after just 30 minutes.

How seminal fluids know to attack other sperm is a mystery. The fact that a brother's sperm also suffers, even though it shares much of the same DNA, suggests that the method involves a blanket attack on anything that isn't recognised as "self". And as with many wars, both sides suffer. It turns out that the protective chemicals from one set of seminal fluids can't counteract the destructive chemicals from another. If the two are mixed, no set of sperm survives very well.

From the queen's point of view, these battles are positively counter-productive. The more sperm she has, the more eggs she can fertilise and the more young she can raise. It's in her interest to stop the sperm from killing each other. Den Boer found that the queens of the leafcutter Atta colombica do just that. The fluids from a queen's spermathecae (the organ where she keeps her sperm supplies) can quell the destructive effect of rival seminal fluids. If they're added to the mix, survival rates for all the stored sperm shoot back up to normal levels. If the sperm wars get too heated, the queen evolves to restores peace for the sake of her future kingdom.

Reference: Science http://dx.doi.org/10.1126/science.1184709 If this link isn't working, read why here

Images: all photos by Susanne den Boer

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Attack of the killer tomato fungus driven by mobile weapons package

Wed, 17 Mar 2010 17:25:01 -0500

In Robert Louis Stevenson's classic story, Dr Henry Jekyll drinks a mysterious potion that transforms him from an upstanding citizen into the violent, murderous Edward Hyde. We might think that such an easy transformation would be confined to the pages of fiction, but a similar fate regularly befalls a common fungus called Fusarium oxysporum.

A team of scientists led by Li-Jun Ma and Charlotte van der Does have found that the fungus can swap four entire chromosomes form one individual to another. This package is the genetic equivalent of Stevenson's potion. It has everything a humble, Jekyll-like fungus needs to transform from a version that coexists harmlessly with plants into a Hyde-like agent of disease. In this guise, it infects so many plant species so virulently that it has earned the nickname of Agent Green and has been considered for use as a biological weapon. It can even infect humans.

These disease-making chromosomes came to light after Ma and van der Does sequenced the genome of a variety of F.oxysporum called lycopersici (or 'Fol'), which infects tomatoes. Its genome was unexpectedly massive, 44% bigger than its closest relative, the cereal-infecting F.verticillioides. Looking closer, Ma and van der Does found that most of this excess DNA lies within four extra chromosomes, which Fol has and its relative lacks. Together, they make up a quarter of Fol's genome.

Ma and van der Does demonstrated the power of this extraneous quartet by incubating a harmless strain of Fol with one that causes tomato wilt. Just by sharing the same space, the inoffensive strain managed to acquire two of the extra chromosomes found in the virulent one. And, suddenly, it too could infect tomatoes. In a single event, the fungus had been loaded with a mobile armoury and changed into a killer. It seems that the fungus needs just two of the four chromosomes to cause disease; the others probably act as accessories, boosting its new pestilent powers.

The extra chromosomes are loaded with a wide variety of jumping genes, parasitic sequences that can hop into new locations under their own steam. Their presence may explain why the fungus can swap large chunks of genetic material with such apparent ease.

Only a fifth of the DNA in these chromosomes consists of protein-encoding genes, but many of these are known players in the infection game. They produce enzymes that break down the tough cell walls of plants and destroy its tissues. But these weapons are very specific. Other varieties of F.oxysporum, which attack different plants, also have extra chromosomes but theirs are very different to those of Fol. While the core genomes of these varieties are 98% identical, most of Fol's extra sequences have no counterpart in other strains and vice versa.

This incredible genetic variety may explain why this particular fungus is so good at infecting different plants. Each variety is armed with its own unique stash of weapons, tailored to the defences of its particular host. Indeed, when Ma and van der Does incubated the innocuous fungus with varieties that infect melons or bananas, it never gained the ability to infect tomatoes. Only another tomato-killer could bestow those powers.

Where did these four chromosomes come from? Their sequences reveal that they are donations from other species of Fusarium. It's a magnificent example of horizontal gene transfer, where living things undercut the slow passage of genes from parent to offspring and simply trade them between individuals.

These genetic swaps are common in bacteria and they too can change from harmless microbes to deadly killers by trading chunks of DNA called "pathogenicity islands". One such package can convert Staphylococcus aureus from a harmless resident of our skin into the agent behind toxic shock syndrome.

We're becoming increasingly aware of similar genetic exchanges in more complex organisms like plants, fungi and even animals, but the transfer of four entire chromosomes - a massive bundle of DNA by anyone's standards - is completely unheard of. These sequences could trigger massive leaps in the evolution of these fungi and their hosts, suddenly triggering epidemics where previously there was harmony.

Reference: Nature http://dx.doi.org/10.1038/nature08850

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Pregnant male pipefish abort babies from unattractive females

Wed, 17 Mar 2010 14:00:29 -0500

For most men, the thought of taking on the burden of pregnancy from their partners would seem like a nightmare, but it's all part and parcel of seahorse life. After mating, female seahorses and pipefish lay their eggs into a special pouch in the male's belly and he carries the developing babies to term. They may seem like a shoe-in for a Dad-of-the-year award but this apparent display of paternal perfection has several macabre twists.

A recent study showed that pregnant pipefishes can also become vampiric cannibals, absorbing some of their brood for nutrition if their own food supplies are running low. Now, Kimberley Paczolt and Adam Jones from Texas A&M University have found that male pipefishes are also selective abortionists. They'll kill off some of the youngsters in their pouches if they've mated with an unattractive female, or if they've already raised a large group of young in an earlier pregnancy.

The pouch isn't just an incubator for the next generation. It's a battleground where male and female pipefish fight a war of the sexes, and where foetal pipefish pay for this conflict with their lives.

Paczolt and Jones studied Gulf pipefish, a species where females mate promiscuously with several males but where males mate with just one female at a time. When the duo acted as pipefish matchmakers, they found that for male pipefish, size matters. They were far more reluctant to mate with smaller females than larger ones.

The pouch of a male Gulf pipefish is transparent and with careful photographs, Paczolt and Jones managed to see each egg, ensconced in its own chamber. These photographs revealed that not only are liaisons with larger females more likely, they're also more successful. The females transfer more eggs to the male's pouch, and a greater proportion of these eggs survive. Throughout the entire sexual experience, from choice to pregnancy, it seems that male pipefish discriminate against smaller partners.

Pipefish females even have to compete against their partners' exes. If the male's last partner was big and provided him with lots of youngsters, the current set of embryos had lower odds of making it out of the pouch alive. It seems that a big pregnancy is a draining experience and a difficult one to pull of twice in a row.

Paczolt and Jones note that the pouch isn't just a sealed box - it's a way for daddy to channel oxygen and nutrients to his kids. If males aren't satisfied with the quality of their mate, they could simply restrict this flow of nutrients from their own body, forcing the siblings to compete for the limited resources and automatically starving out the weakest ones. Any youngsters that die could even be recycled. Earlier this year, another group of scientists showed that amino acids from pipefish eggs sometimes end up in the tissues of the male that supposedly carried them. Daddy, it seems, was cannibalising some of his kids.

Another interesting possibility is that the females are influencing the pouch wars too. A larger female could produce eggs that are better at harvesting nutrients from their father, or they could lace the male with chemicals that increase his investment. But if these scenarios were true, you would expect that after a large and exhausting pregnancy, drained males would actually pursue smaller females. In fact, the opposite happens. That suggests that the males are the ones with the final say over the embryos' fates.

These sorts of sexual conflicts are common in the animal kingdom. But this is the first time they've been documented in an animal where the traditional sex roles of pregnant females and promiscuous males have been swapped. These results cast the pouch of a male pipefish or seahorse in a new light. It's still a nurturing bag that shelters and provides for youngsters but it's also a way for males to control their investment in the next generation. The pouch is the male's secret weapon in the battle of the sexes.

Reference: Nature http://dx.doi.org/10.1038/nature08861 If this link isn't working, read why here

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The value of "this is cool" science stories

Tue, 16 Mar 2010 08:30:15 -0500

A couple of nights ago, I discovered a blog by Canadian science journalist Colin Schultz, who is doing a series of interviews with eminent science journalists including Carl Zimmer, Nicola Jones, David Dobbs and Jay Ingram. They're great reads and I especially liked the stark differences in the answers from Nicola Jones and Carl Zimmer, particularly about the sorts of stories they like to tell.

Jones says, "The really fulfilling stories are the ones that come, I think, spinning out of real world events." She is interested in how science "relates to policy developments" or "to things that are going on in the real world." Carl, on the other hand, says, "I think a lot of science writers actually try to search a little too hard for that 'news you can use' when it comes to science. A lot of science is just interesting in and of itself. And it just sort of gives you a richer understanding of the world, and there really isn't any need to make wild claims about a cure for cancer right around the corner"

My approach is far more aligned to Carl's. I often tell stories on this blog with absolutely no practical relevance. Their goal is to instil a sense of wonder and curiosity about the world, which is what the best science communicators have done for me. As I said in my own 'twitterview' with Colin (see below), we shouldn't "underestimate the power of 'this is cool' stories."In the short term, current affairs and political decisions provide nice, obvious hooks with which to explain science to a mass audience. But in the long-term, I suspect that stories that evoke a sense of awe and excitement are what truly get people to regularly engage with science, its methods and its processes.

None of this is intended to suggest that "this-is-cool" stories are somehow superior to those explaining the interaction between science, policy and society, or what David Dobbs calls the "smells funny" stories. They are simply the stories that I prefer to tell. Individual journalists can specialise in one or more of these areas but across the science writing population, we ultimately need a mix of approaches.

Richard Dawkins famously ~~said~~ quoted a New Scientist editor in saying, "Science is interesting, and if you don't like it, you can f**k off."The problem is that a lot of people have clearly taken him up on his advice. Reaching people who aren't already interested in science has always been one of the main challenges of science communication. The varied nature of newspaper spreads provide opportunities for drawing people's attention to stories they might not have deliberately sought out. Tablet readers have an outside chance of duplicating this effect. But for now, as newspapers decline and shrink, the worry is that the internet will only cater for established interests. As Colin asks, "All of my interviews have pointed out that strong story and strong characters can get someone to read your science story, but what if they don't open the section?"

Opening a section, of course, is an example of "pull marketing", where users and consumers yank in the information that they actively demand. But the internet's strengths will increasingly rely on "push marketing" where people foist material towards consumers. This isn't just about traditional paid advertising. Social media ensures that we are all each others' editors and advertisers. Through email, Facebook, Twitter, Delicious, Buzz and more, we shove content into the attentional spotlights of our contacts.

And this is an area where "this-is-cool" stories really excel. Indeed, by far the most popular stories on NERS are the ones that are interesting for their own sake. I've noticed that if I write about medical breakthroughs (yes, even the ones that are actually breakthroughs), they generally get less traction than stories about, say, an amazing new piece of animal behaviour. People care when doctors use genome sequencing to reverse a faulty diagnosis, but they apparently care even more when scientists reveal the colours of dinosaur feathers. Bigger institutions report similar trends. Science stories feature prominently on the New York Times's list of most emailed articles. An analysis of this list revealed that "readers wanted to share articles that inspired awe".

"Science kept doing better than we expected," said Dr. Berger, a social psychologist and a professor of marketing at Penn's Wharton School. "We anticipated that people would share articles with practical information about health or gadgets, and they did, but they also sent articles about paleontology and cosmology. You'd see articles shooting up the list that were about the optics of deer vision."

There are myriad and unpredictable reasons why readers will share stories with each other. Good journalists always try to write with audiences in mind, finding angles that will pique their readers' interests. But in terms of working out your readers' interest, the internet is smarter than you. It has the ability to push stories to unexpected audiences for reasons that you might never have anticipated.

Last week, I wrote a piece about sex determination in chickens and the surprising discovery that every chicken cell has its own male or female sexual identity. A day later, a friend of mine told me, via Facebook, that the story had inspired her chicken-keeping friends. This has happened time and again. A piece about ballet postures becoming more extreme over time was posted on several ballet forums. A statistical analysis of the lack of female chess grandmasters reached a substantial chess-playing community after a female grandmaster linked to it from her own blog. And then there's always Carl's now famous (infamous?) duck sex example.

None of these case studies involved sci-curious people actively pursuing their interests. They didn't involve discoveries that are going to change or save the world. They involved people being fed interesting science stories by their pals and peers, purely on the basis that they were interesting. In this way, this blog accumulates readers who aren't initially interested in science. I know this happens, because I get emails from them and because NERS appears on some blogrolls in absence of any other science blogs. Perhaps Dawkins's quote should be amended to "Science is interesting, and if you don't like it, we'll get your friend to convince you."

An aside about Twitterviews

All of this started when I mentioned on Twitter that I liked Colin's interviews. That prompted a brief but interesting transatlantic conversation with him about science journalism, all delivered in 140-character tweets while Colin was apparently on the bus and I was sitting on my sofa writing about sperm. I shut down Tweetdeck to do some actual writing and was a bit surprised to open it a few hours later to find that Colin had stuck up our conversation on this blog as a "twitterview". All abbreviations were stretched out but no words were added.

I love it. It's a great example of how an informal chat can turn into something perhaps more substantial and how social media like Twitter can provide ideas and material for opportunistic writers. I'm also quite pleased with the fact that the conversation seems rather cogent, despite the often-cited limitations of the channel. Of course, said limitations make it difficult to really delve deeply into a topic, so this post expands on some of the ideas we talked about and acts as a response to Colin's post.

Image: by the legendary Bill Watterson, but you knew that already.

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Bacteria on your keyboard point to your identity but forensic value is unlikely

Mon, 15 Mar 2010 15:00:22 -0500

We all know that as we type on our keyboards or click our mice, we leave behind fingerprints that could be used to deduce our identities. But these prints aren't the only remnants of our presence. Bacteria from our skins also linger on the things we touch and they could act as a sort of living fingerprint.

The thriving community of bacteria and other microscopic passengers on our skin has many traits of interest to a forensic scientist. For a start, they are remarkably personal in their membership and stable over time. Just 13% of the bacteria on my palm also live on yours, and even identical twins can harbour very different microbes. Even after we give our hands a good wash, our individual communities eventually bounce back with a similar mix of members. Skin bacteria are also easy to dislodge. As we go about our daily lives, we leave a trail of our own personal bacteria on the things we touch, which can stick around for days or weeks.

Noah Fierer from the University of Colorado has found some preliminary evidence that these dislodged microbes could help to identify an individual. He showed that bacteria swabbed from keyboards and mice matched the microbes on their owner's skin more closely than those from other people. It's a promising technique, but David Foran, director of Michigan State University's Forensic Biology Laboratory, says that it's "utility in a forensic context is doubtful". It's unlikely to ever meet the high standards of certainty needed for a criminal investigation, although that probably won't stop it from appearing in a future episode of CSI.

Fierer swabbed the keys of three computer keyboards as well as the fingers of their owners. By sequencing the DNA of the bacteria he found, he showed that the communities on keys and fingertips are a close match. They could be used to tell the three people apart, even though two of them share the same office.

All of these samples were taken an hour or so after the owners had last typed on their keys, but Fierer found that leftover bacteria can stand longer tests of time. After swabbing the skins of two volunteers, he found that two weeks later, the bacteria were still informative and the communities were unchanged, even if the swabs were kept in open containers at room temperature.

So far, that's not particularly impressive. Three is a vanishingly small number if we're seriously talking about applications in forensics. So for his next trick, Fierer sequenced bacteria from nine computer mice. He compared them to sequences from bacteria on the mouse owners' hands and to a database of similar sequences from 270 people who had never touched the devices. In every case, the mouse microbes were significantly more similar to the communities on their owners' hands than to those from the other 278 people.

Even after this promising result, Fierer is very measured about the prospects for this technique. Like other widely used forensic tools, identification by skin bacteria would need to undergo a lot of development and refinement before it could actually be used in investigations. This is just a 'proof-of-principle', an inkling that this technique is worth more research.

Would it work on a wide variety of surfaces, on objects that aren't touched as often as keyboards or mice, or on those that are touched by different parts of the skin? Could certain bacteria give away their owner's identity more than others? Would a database of hand bacteria be useful? And how would you deal with objects that had been touched by several people?

If this work pans out, Fierer suggests that skin bacteria could be used to provide independent confirmation for other lines of evidence such as DNA or fingerprint analyses. After all, the bacteria in and on your body outnumber your cells by a factor of 10, and their genes outnumber yours by a factor of 100. It's possible that the genes of these residents might be more useful in establishing our identities than our own genes.

But Foran is much more sceptical. He says that Fierer uses the word "match" throughout his paper but the word has a very specific meaning in forensics. "[A match] means that there are absolutely no incongruities between the data produced from a questioned sample and those from a known sample," he explains. That's very different to saying that a bacterial sample is more similar to those from person A than person B. "Perhaps it can be said it seems more likely person A touched an object than did person B, however we definitely cannot say person A did touch the object."

The problem is that forensics requires a far higher threshold of certainty than skin bacteria are likely to provide. Foran notes that if a fingerprint is a 90% match to a questioned print, a forensic scientist would conclude that that person didn't leave the print. Likewise, a DNA sample that's 10% different would be a negative result, although in that case, you might look for a relative. He says, "The method presented will probably never lead to a match; given the huge amount of bacterial variability the authors find over time and even among different body parts, finding a true DNA match between questioned and knowns would be next to impossible. It would be far easier for the defense to argue that the suspect did NOT leave that bacterial profile."

Reference: PNAS http://dx.doi.org/10.1073/pnas.1000162107If this link isn't working, read why here

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Pocket Science - a psychopath's reward, and the mystery of the shark-bitten fossil poo

Mon, 15 Mar 2010 08:30:13 -0500

Not Exactly Pocket Science is a set of shorter write-ups on new stories with links to more detailed takes by the world's best journalists and bloggers. It is meant to complement the usual fare of detailed pieces that are typical for this blog.

The rewarding side of being a psychopath

What goes on in the brains of psychopaths? They can seem outwardly normal and even charming, but tthese people typically show a lack of empathy, immoral behaviour and an impulsive streak. Joshua Buckholtz found that the last of these traits - impulsivity - may stem from a hyperactive reward system in the brain and unusually high levels of the signalling chemical dopamine.

When given small doses of amphetamines, people who come out as more impulsive on tests of psychopathy also released more dopamine in a part of their brain called the nucleus accumbens. This region plays many roles in feelings of reward, pleasure and addiction. This link between it and the impulsive side of psychopathy remained even after adjusting for other personality traits. Even the prospect of winning money, as opposed to a physical drug, triggered a hyperactive response from the nucleus accumbens.

When a psychopath imagines a future reward, the explosion of dopamine in their brain provides them with incredible motivation to get that reward. This extra motivation could underlie the increased drug use and the impulsive streaks that accompany the condition. It could even explain some of the antisocial behaviour - dopamine's most familiar as a chemical linked to feelings of reward and pleasure but studies in mice suggest that its presence in the nucleus accumbens is vital for aggression.

Previous research in this area has focused on the emotionally cold side of psychopathy, which may stem from problems in other parts of the brain like the amygdala, involved in emotions, and the ventromedial prefrontal cortex (vmPFC), involved in fear and risk. The impulsive side of the disorder has typically been overlooked but it predicts many of the problems associated with psychopathy, including drug abuse and violent criminal behaviour.

Reference: Nature Neuroscience http://dx.doi.org/10.1038/nn.2510

Image by Gregory R.Samanez-Larkin and Joshua W. Buckholtz

Why did the shark bite the poo?

The specimen on the right is a most unusual one. It's a coprolite, a piece of fossilised dung. That's not unique in itself; such specimens are often found and they tell us a lot about what extinct animals ate. But this one has a line of grooves running down its middle. They were made by a shark.

Stephen Godfrey and Joshua Smith found two such specimens in Maryland's Chesapeake Bay. The identity of the coprolites' maker is a mystery, but its chemical composition suggests that they were excreted by a meat-eating vertebrate. The identity of the biter is clearer. The duo poured liquid rubber into the grooves to make a model cast of the teeth that made them. These model teeth made it clear that the biter was a shark and the duo even managed to narrow its identity down to one of two species -a tiger shark, or Physogaleus, a close extinct relative.

Why would a shark bite a piece of dung? Tiger sharks are notorious for their ability to eat just about anything, but obviously, neither piece of dung was actually swallowed. No known shark eats poo for a living. The shark may have had an exploratory bite and didn't like what they tasted. But Godfrey and Smith's favourite explanation is that the bites were the result of collateral damage - the shark attacked an animal and during its assault, it happened to bite through the bowels. These specimens are the enduring remains of a battle between two predators, as suggested by this wonderful drawing in the paper by T Schierer of the Calvert Marine Museum.

Reference: Godfrey, S., & Smith, J. (2010). Shark-bitten vertebrate coprolites from the Miocene of Maryland Naturwissenschaften DOI: 10.1007/s00114-010-0659-x

'Wasabi protein' responsible for the heat-seeking sixth sense of rattlesnakes

Sun, 14 Mar 2010 14:00:18 -0500

Take a whiff of mustard or wasabi and you'll be hit with a familiar burning sensation. That's the result of chemicals in these pungent foods hitting a protein called TRPA1, a molecular alarm that warns us about irritating substances. The same protein does a similar job in other animals, but rattlesnakes and vipers have put their version of TRPA1 to a more impressive and murderous purpose. They use it to sense the body heat of their prey.

Pit vipers are famed for their ability to detect the infrared radiation given off by warm-blooded prey, and none more so than the western diamondback rattlesnake. Its skills are so accurate that it can detect its prey at distances of up to a metre, and strike at objects just 0.2C warmer than the surrounding temperature. Against such abilities, darkness is no defence.

Like all pit vipers, the rattlesnake's sixth sense depends on two innocuous pits located between their eyes and their nostrils. With two pits on either side of its head, the snake can even 'see' heat in stereo. Each pit is a hollow chamber with a thin membrane stretched across it, which acts as an "infrared antenna". It is loaded with blood vessels, energy-harvesting mitochondria and dense clusters of nerves. The nerves connect with the visual parts of the snake's brain, allowing it to match up images of both heat and light. So far, so clear, but until now, no one knew how the membranes actually worked.

Elena Gracheva and Nicolas Ingolia, from the University of California, San Francisco, have solved the mystery but it wasn't easy. Rattlesnakes don't give up their secrets readily. Their genes have rarely been sequenced and, in what must be the understatement of the year, Gracheva and Ingolia describe them as "genetically intractable" and "inconvenient subjects for physiological and behavioural studies". To translate: if you're looking for a model animal to work with, you're probably better off with fruit flies and zebrafish than a four-foot serpent with a deadly bite.

The duo suspected that the proteins responsible for the rattlesnake's heat-seeking powers would probably be found in the unusually large nerve endings that suffuse its pit membrane. They analysed the active genes in these nerve endings, and compared them to those running down the snake's spine.

In mammals, the two types of nerves have virtually identical portfolios of active genes. The same is true for snakes like the Texas rat snake or the western coachwhip, neither of which can sense infrared. But in the rattler, Gracheva and Ingolia spotted an unmissable difference - a single gene that encodes the TRPA1 protein was 400 times more active in the pit nerves than the spinal ones.

In humans, TRPA1 is activated by allyl isothiocyanate, the chemical that gives wasabi and mustard their kick. The rattler's protein, which is 63% identical to ours, responds to the same chemical but more weakly. It is, however, exquisitely sensitive to heat. At room temperature, the protein is idle. But anything over 27.6C will set it off and the higher the temperature, the more active the protein. By comparison, a rat snake's version of TRPA1 is also sensitive to heat, but it responds more weakly than that of the rattler, and at a higher threshold temperature.

Two other groups of snakes, the pythons and boas, can detect infrared radiation, although their technology is 5-10 times less sensitive than the sophisticated viper hardware. They also have pits but theirs are spread across their snouts, are simpler in structure and have fewer nerve connections. But Gracheva and Ingolia found that they have independently co-opted the same molecule in their pursuit of hot sensory action, even though their ancestors diverged from those of vipers 30 million years ago.

In invertebrates like flies and worms, TRPA1 also plays a role in sensing temperature changes. In vertebrates, it's more to do with sensing foul chemicals and possibly cold temperatures but it seems that three groups of snakes have revived the ancient function of these proteins.

And now a question for the audience: Infrared detection seems like an extremely valuable skill, so why is it that only two groups of snakes have evolved it? If it's all done by co-opting the same apparently malleable protein, why isn't the strategy more common? I asked the lead author but he had no answer either. Any thoughts?

Reference: Gracheva, E., Ingolia, N., Kelly, Y., Cordero-Morales, J., Hollopeter, G., Chesler, A., Sánchez, E., Perez, J., Weissman, J., & Julius, D. (2010). Molecular basis of infrared detection by snakes Nature DOI: 10.1038/nature08943

Subliminal flag shifts political views and voting choices

Fri, 12 Mar 2010 08:30:21 -0500

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

For all the millions that are poured into electoral campaigns, a voter's choice can be influenced by the subtlest of signals. Israeli scientists have found that even subliminal exposure to national flags can shift a person's political views and even who they vote for. They managed to affect the attitudes of volunteers to the Israeli-Palestine conflict by showing them the Israeli flag for just 16 thousandths of a second, barely long enough for the image to consciously register.

These results are stunning - even for people right in the middle of the one of the modern age's most deep-rooted conflicts, the subconscious sight of a flag drew their sympathies towards the political centre.

In some ways, it's not surprising. The last decades of experimental psychology have shown us that the our conscious view of the world is a construct created by our brain. We simply cannot consciously process the barrage of information constantly arriving through our senses and to save us from a mental breakdown, our brain does a lot of subconscious computing. The upshot of this is that our decisions can be strongly influenced by sights, sounds and other stimuli that we're completely unaware of. Have a look at this video of mind-manipulator Derren Brown for a classic example of this.

Our political views are no different. In an ideal world, we would base them on a rational consideration of the relevant facts and our own beliefs, but in the real one, subliminal symbols pull on the puppet-strings too. National flags should be capable of this; to many people, they carry a weighty importance out of all proportion to their nature as rectangular sheets of cloth

Ran Hassin from Hebrew University and Melissa Ferguson from Cornell University have clearly demonstrated this by showing subliminal images of flags to Israeli volunteers. Their partners, Daniella Shidlovski and Tamar Gross, asked 53 people about how strongly they identified with Israeli nationalism and how being an Israeli affected their identity. According to their responses, they were separated into a High or Low based on their penchant for nationalism.

They were then asked to answer on-screen questions, half of which were about the Israeli-Palestine conflict (read the full list here). The answers worked on a scale from one to nine, with nine reflecting the most strongly nationalistic attitudes. Before the questions came up on screen, the researchers briefly showed the volunteers an image of the Israeli flag (right above) or a control flag (right below) with the same elements jumbled up. The flags flashed up so quickly that none of the volunteers saw it, even when they were explicitly quizzed about it later.

When they were shown the control flag, the High group, as expected answered the on-screen questions with a nationalistic bent, averaging a score of 6. The Low group's average score was closer to 2.5. However, when both groups saw the subliminal Israeli flag, they both converged to a middle-ground score of 4.

Sixteen milliseconds of exposure to the flag was enough to close the ideological gap between the two groups. In a second experiment, Hassin showed that the flashed flag had the same moderating effect on opinions about Jewish settlers in the West Bank and Gaza. At this point, it's worth noting that the flags didn't wield an irresistible mind-altering power. There was still variation in the volunteer's choices, but the average trend changed in a statistically significant way.

In a final test, Hassin and Ferguson repeated their experiment in a real-world setting, before and after a local election. They worked with 101 new volunteers and asked them to reveal who they were planning on voting for before the event, and who they eventually voted for. The candidates were given a score from 1 to 6, with higher scores reflecting right-wing stances and lower ones reflecting left-wing ones.

Amazingly, they found the same effect. Volunteers who saw the subliminal real flags, but not the control ones, claimed that they were more likely to vote for the center candidates, and actually did so. It's a shocking testament to the power of subliminal imagery - a quick flash in a laboratory can prime a person's behaviour some time later. It can even affect the most important political action of all - voting.

Hassin's group note that they've uncovered a fascinating phenomenon but they're still in the dark about how it works. Do the symbols affect the weight we give to different views or do they affect our innate biases? Why does the Israeli flag drive people towards the political centre, and would symbols used by more extreme ideologies shift political stances away from it?

The answers to the questions will have to wait. For now, the study serves to reiterate how important a simple symbol can be.

Reference: Hassin, R., Ferguson, M., Shidlovski, D., & Gross, T. (2007). Subliminal exposure to national flags affects political thought and behavior Proceedings of the National Academy of Sciences, 104 (50), 19757-19761 DOI: 10.1073/pnas.0704679104

Image: by MathKnight and Zachi Evenor

More on voting and the Israeli-Palestinian conflict:

Pocket Science - geneticist hunts down the cause of his own genetic disorder, and male moths freeze females by mimicking bats

Thu, 11 Mar 2010 14:53:56 -0500

Geneticist sequences own genome, finds genetic cause of his disease

If you've got an inherited disease and you want to find the genetic faults responsible, it certainly helps if you're a prominent geneticist. James Lupski (right) from the Baylor College of Medicine suffers from an incurable condition called Charcot-Marie-Tooth (CMT) disease, which affects nerve cells and leads to muscle loss and weakness.

Lupski scoured his entire genome for the foundations of his disease. He found 3.4 million placed where his genome differed from the reference sequence by a single DNA letter (SNPs) and around 9,000 of these could actually affect the structure of a protein. Lupski narrowed down this list of candidates to two SNPs that both affect the SH3TC2 gene, which has been previously linked to CMT. One of the mutations came from his father and the other from his mother. Their unison in a single genome was the cause of not just Lipson's disease but that of four of his siblings too.

It's a great example of how powerful new sequencing technologies can pinpoint genetic variations that underlie diseases, which might otherwise have gone unnoticed. The entire project cost $50,000 - not exactly cheap, but far more so than the sequencing efforts of old. The time when such approaches will be affordable and commonplace is coming soon. But in this case, Lupski's job was easier because SH3TC2 had already been linked to CMT. A second paper tells a more difficult story.

Jared Roach and David Gallas sequenced the genomes of two children who have two inherited disorders - Miller syndrome and primary ciliary dyskinesia - and their two unaffected parents. We don't know the genetic causes of Miller syndrome and while the four family genomes narrow down the search to four possible culprits, they don't close the case.

For great takes on these stories and their wider significance, I strongly recommend you to read Daniel Macarthur's post on Genetic Future, Mark Henderson's piece in the Times and Nick Wade's take in the NYT (even if he does flub a well-known concept). Meanwhile, Ivan Oranksy has an interesting insight into the political manoeuvres that go into publicising two papers from separate journals. And check out this previous story I wrote about how genome sequencing was used to reverse the wrong diagnosis of a genetic disorder.

Reference: http://dx.doi.org/10.1056/NEJMoa0908094 and http://dx.doi/org/10.1126/science.1186802

Male moths freeze females by mimicking bats

Flying through the night sky, a moth hears the sound of danger - the ultrasonic squeak of a hunting bat. She freezes to make herself harder to spot, as she always does when she hears these telltale calls. But the source of the squeak is not a bat at all - it's a male moth. He is a trickster. By mimicking the sound of a bat, he fooled the female into keeping still, making her easier to mate with.

The evolutionary arms race between bats and moths has raged for millennia. Many moths have evolved to listen out for the sounds of hunting bats and some jam those calls with their own ultrasonic clicks, produced by organs called tymbals. In the armyworm moth, only the males have these organs and they never click when bats are near. Their tymbals are used for deceptive seductions, rather than defence.

Ryo Nakano found that the male's clicks are identical to those of bats. When the males sung to females, Nakano found that virtually all of them mated successfully. If he muffled them by removing the tymbals, they only got lucky 50% of the time. And if he helped out the muted males by playing either tymbal sounds or bat calls through speakers, their success shot back up to 100%. Nakano says that this is a great example of an animal evolving a signal to exploit the sensory biases of a receiver.

More on bats vs. moths from me

Reference: Biology Letters http://dx.doi.org/10.1098/rsbl.2010.0058

Every cell in a chicken has its own male or female identity

Wed, 10 Mar 2010 13:40:22 -0500

The animal on the right is no ordinary chicken. Its right half looks like a hen but its left half (with a larger wattle, bigger breast, whiter colour and leg spur) is that of a cockerel. The bird is a 'gynandromorph', a rare sexual chimera. Thanks to three of these oddities, Debiao Zhao and Derek McBride from the University of Edinburgh have discovered a truly amazing secret about these most familiar of birds - every single cell in a chicken's body is either male or female. Each one has its own sexual identity. It seems that becoming male or female is a very different process for birds than it is for mammals.

In mammals, it's a question of testicles, ovaries and the hormones they produce. Embryos live in sexual limbo until the sex organs (gonads) start to develop. This all depends on a sexual dictator called SRY, a gene found on the Y chromosome. If it's present, the indifferent gonads go down a male route; if not, they take a female one. The sex organs then secrete a flush of hormones that trigger changes in the rest of the body. The sex chromosomes are only relevant in the cells of the gonads.

But the gynandomorphs show that something very different happens in birds. Birds have Z and W chromosomes; males are ZZ and females are ZW. Zhao and McBride used glow-in-the-dark molecules that stick to the two chromosomes to show that the gynandromorphs do indeed have a mix of ZZ and ZW cells. However, they aren't split neatly down the middle. Their entire bodies are suffused with a mix of both types, although the male half has more ZZ cells and the female half has more ZW ones.

Even though the three chickens were both male and female, one of them only had a testicle on one side, the second only had an ovary on one side, and the third had a strange hybrid organ that was part testis and part ovary. These malformed organs pumped the same soup of hormones throughout the birds' bodies but, clearly, each side responded differently.

Zhao and McBride started to suspect that each cell has its very own sexual identity, and that this individuality exists from the chicken's first days of embryonic life. They proved that by transplanting cells from embryonic sex organs from one animal to another. All the transplants produced a glowing green protein so Zhao and McBride could track their whereabouts, and those of their daughters.

If they were shoved into the midst of other cells of the same sex, they were integrated into the developing sex organs. But if they were placed amid cells of the opposite sex, they became ostracised. In mammals (say, a mouse), an XX cell can become a working part of the testes just as an XY cell can become a working part of the ovaries. But birds cannot be cajoled into switching sides. Male and female cells clearly retain their identity even if they're exiled into new surroundings.

As an exception that proved the rule, Zhao and McBride did manage to create an embryo with hybrid "ovo-testis" sexual organs, by transplanting a lot of female cells into a male embryo. The female cells could respond to signals from their new male home telling them to make sexual tissues. But they responded according to their own internal program, producing female structures and deploying female-specific enzymes.

Zhao and McBride think that right from the first few days of development, a battle of molecules in every cell sets their sexual identities. Depending on whether they're ZZ or ZW, the cells activate a sex-specific cadre of genes. For example, a gene called FAF (female-associated factor; no jokes from British readers please) is strongly activated throughout a female embryo less than a day after fertilisation. Meanwhile, male embryos have 10 times the level of an RNA molecule called mir-2954 than their female peers.

At this early stage, the activity of these genes means that a bird embryo is already male or female, even though no sexual organs have developed. The genes then set the genitals down the appropriate developmental path. These organs pump out hormones that certainly influence the rest of the animal, but unlike in mammals, they don't wield any true power. They are just figureheads; there is no equivalent of the mammalian SRY gene, no sexual dictator giving orders.

A similar process might even operate in some mammals. In the wallaby, a marsupial, the SRY gene is active throughout the entire embryo before the point where the sexual organs form, and some of these organs like the breasts and scrotum develop without the influence of sex hormones. Who knows whether other groups of back-boned animals, like fish or reptiles, do something similar?

The fact that something as seemingly straightforward as being male or female could be so complicated in an animal as familiar as a chicken tells us just how much wonder there is left to uncover in the natural world.

UPDATE: This diagram explains the differences between the chicken and mammal systems. The "genital ridge" is the embryonic tissue that the gonads develop from. Note that in mammals, it is sexually neutral until the SRY gene turns it into ovaries or testes - at that point, hormones set the individual's body (its 'phenotype') as male or female. In chickens, the cells of the body (the 'soma') are already male or female long before this happens. The development of the genital ridge into ovaries or testes (which may or may not be influenced by the DMRT1 gene), and the hormone soup that's produced afterwards, don't really change things that much.

Reference: Zhao, D., McBride, D., Nandi, S., McQueen, H., McGrew, M., Hocking, P., Lewis, P., Sang, H., & Clinton, M. (2010). Somatic sex identity is cell autonomous in the chicken Nature, 464 (7286), 237-242 DOI: 10.1038/nature08852

More on sex determination:

Science in the Media: Rude or Ailing Health?

Wed, 10 Mar 2010 08:30:19 -0500

If anyone's in London or thereabouts on the 31st of March, come and see me and a few other science journalists discuss the state of science in the media at City University. The discussion follows a recent government report, entitled Science in the Media: Securing the Future. The report declared that science coverage (in the UK, at least) was in "rude health", while is somewhat different to the picture that others have painted.

I'll be discussing the report as well as, presumably, other matters about science journalism along with a panel of veteran UK journalists. I assume that I have been recruited as the voice of youthful dissent and indeed, those of you who were at my panel at ScienceOnline may remember me reading out a passage from this same report to the sound of laughter from the crowd.

Personally, I think the report has a lot of good things to say, but it's missing any substantial discussion about the new ecosystem of online science journalism and the changing nature of those who can legitimately call themselves science journalists. But enough for now - come along and join the discussion. It should be a good one.

The official description is below and you need to reserve a place.

I'd also like to encourage people who attend to tweet it. Perhaps #scimedia as a hashtag.

Date: Wednesday 31 March 2010

Time: 6.30pm

Location: City University London, Northampton Square, London EC1V 0HB

A recent government report on science in the media declared that it was in "rude health", while other commentators think that it is ailing and in crisis.

Join the debate with a panel of leading science journalists including:

Pallab Ghosh (BBC)

Natasha Loder (Economist)

Andrew Jack (Financial Times)

Ed Yong (Not Exactly Rocket Science blog)

Fiona Fox (Science Media Centre and author of the report)

DNA from the largest bird ever sequenced from fossil eggshells

Tue, 09 Mar 2010 19:00:31 -0500

Even extinction and the passing of millennia are no barriers to clever geneticists. In the past few years, scientists have managed to sequence the complete genome of a prehistoric human and produced "first drafts" of the mammoth and Neanderthal genomes. More controversially, some groups have even recovered DNA from dinosaurs. Now, a variety of extinct birds join the ancient DNA club including the largest that ever lived - Aepyornis, the elephant bird.

In a first for palaeontology, Charlotte Oskam from Murdoch University, Perth, extracted DNA from 18 fossil eggshells, either directly excavated or taken from museum collections. Some came from long-deceased members of living species including the emu, an owl and a duck. Others belonged to extinct species including Madagascar's 3-metre tall elephant bird and the giants moas of New Zealand. A few of these specimens are just a few centuries old, but the oldest came from an emu that lived 19,000 years ago.

It turns out that bird eggshells are an excellent source of ancient DNA. They're made of a protein matrix that is loaded with DNA and surrounded by crystals of calcium carbonate. The structure shelters the DNA and acts as a barrier to oxygen and water, two of the major contributors to DNA damage. Eggshells also stop microbes from growing and it seems that ancient ones still do the same. Oskam found that the fossil shells had around 125 times less bacterial DNA than bones of the same species did.

This is important - bacteria are a major problem for attempts to extract ancient DNA and they force scientists to search for uncontaminated sources, like frozen hair. Eggshells, it seems, provide similarly bacteria-free samples. Still, Oskam's team took every precaution to prevent contamination. They used clean rooms and many control samples. Many of their sequences, like those of Aepyornis, were checked by two independent laboratories.

The Aepyornis sequences are particularly encouraging because many scientists have previously tried to extract DNA from the bones of this giant and failed. Eggshells seem like a more promising source and it certainly helps that the eggs of many of these giant species were massive and thick. But Oskam did also recover DNA from a fossil duck egg, which suggests that it should be possible to sequence the genes of even small extinct birds, like the dodo.

So far, the team have proved that they can extract the DNA. It's what they do with it that counts. It's worth remembering that fossil eggshells have already helped palaeontologists to date the remains of ancient birds, and reconstruct their diets and lifestyles. Some even clue us into the artistic traditions of our own ancestors.

Oskam is now analysing around 400 pieces from sites around New Zealand to understand how humans interacted with the moas and how our zealous hunting drove them to extinction. There were several different species of moa that are difficult to tell apart - egg DNA could help Oskam to do just that. The same technique could be used to study the last days of other extinct birds with interesting evolutionary histories, including the great auk, Haast's eagle and that poster child for extinction, the dodo.

Mike Bunce, who led the study, is keen to try and release ancient DNA from eggshells all around the world. "Given frozen environments preserve DNA 'better', we are very keen to examine any eggshell finds from 'old' sediments, such as seabird nesting sites, in the Arctic and Antarctic," he says. And the door should now be open for other researchers to do the same. After all, in finding out how to extract DNA from eggshells, Oskam tested a variety of methods to develop the most efficient possible protocol.

Still, it's clear that the technique has limitations. Oskam tried to extract DNA from the 50,000-year-old shell of Genyornis, a giant Australian bird that lived in a very hot climate. She failed. And as Bunce clearly stresses, "This is not a technique that is applicable to fossil dinosaur eggs."

Update: That hasn't stopped the idiotic headline writers to London's Metro newspaper from claiming that "Jurassic Park has just taken a giant T-Rex-sized step toward becoming reality after ancient DNA from long-extinct creatures was successfully extracted." Amusingly, the claim that dinsoaur DNA has been rebuilt is technically true given that birds are living dinosaurs. And if the subeditor who wrote the headline and standfirst and chose the picture actually knew that, I'd be surprised.

Reference: Oskam, C., Haile, J., McLay, E., Rigby, P., Allentoft, M., Olsen, M., Bengtsson, C., Miller, G., Schwenninger, J., Jacomb, C., Walter, R., Baynes, A., Dortch, J., Parker-Pearson, M., Gilbert, M., Holdaway, R., Willerslev, E., & Bunce, M. (2010). Fossil avian eggshell preserves ancient DNA Proceedings of the Royal Society B: Biological Sciences DOI: 10.1098/rspb.2009.2019

More on ancient DNA:

Pocket Science - chameleons hunt with cold-proof tongues and zebrafish babies go blind at night

Tue, 09 Mar 2010 08:30:09 -0500

Cold-proof tongue allows early chameleon to catch early insect

Chameleons are some of the most versatile of lizards. They live in baking deserts and freezing mountaintops and part of their success hinges on a weapon that works just as well in the warmth as in the cold - its tongue. Relying on stored elastic power for its ballistic strike, the chameleon's tongue is largely cold-proof. At temperatures that would flummox most reptile muscles, the tongue carries on snatching insects with great efficiency.

Chameleon tongues can reach twice the length of their body in less than a tenth of a second, latching onto prey with a sticky, grasping tip. Rather than pushing it forward with muscle power, like a spear-thrower, the chameleon behaves more like an archer. It ratchets the tongue backwards by slowly contracting its muscles, as if it was drawing an arrow on a bow. It fires by relaxing its muscles, and the whole sticky snare shoots forward on its own momentum. Once the prey is caught, long muscles pull the tongue back into the mouth.

Christopher Anderson and Stephen Deban from the University of South Florida filmed veiled chameleons with a high-speed camera as they shot their tongues at dangling crickets. Their performance certainly improved as the temperature increased from 15 to 35C, but not by much. Even at low temperatures, the tongue shot out with impressive acceleration, speed and power that fell by just 10-20% across a ten degree gradient. When it retracted under muscular control, the effects of the chill were more obvious and a similar gradient led to a 40-60% fall in performance.

By freeing their killer strike from the constraints of temperature, chameleons have been able to exploit chilly windows of opportunity denied to other lizards. They can hunt during the early morning hours when insects are very active and they can expand across a wide range of habitats. They also have to waste less energy on the simple business of keeping warm. After all, why bother with central heating when you can catch food at body temperatures of 3.5C, as some chameleons can?

Reference: PNAS http://dx.doi.org/10.1073/pnas.0910778107If this link isn't working, read why here

Image by Christopher V Anderson

Zebrafish babies shut off their eyes at night

Many animals find it harder to see in the darkness of night, but the larvae of zebrafish must find it particularly difficult. Every night, they essentially shut down their eyes, losing the ability to see. Fairda Emran found that the retinas of the baby fish responded normally to light during the day, but they were almost totally impassive after 90 minutes of darkness. The fish themselves totally failed to follow a moving target.

The babies' body clocks drove this cycle of blindness. It kicked in every night and even if the fish were kept in darkness for several days, they always anticipated the arrival of daylight by restoring their sight. Only a flash of light at night managed to break this tidy cycle, restoring the zebrafishes' vision at a time when they would normally be blind.

At five days of age, baby zebrafish have just used up all the yolk from their eggs and are starting to find their own food. For them, energy is a precious commodity and eyes are energy-guzzling appliances, even when they're set to standby at night. It makes sense to just shut them off instead.

Reference: PNAS http://dx.doi.org/10.1073/pnas.0914718107 If this link isn't working, read why here

More from NERS on how animal eyes cope with darkness, including animals that use DNA as lenses, squid that have bacterial flashlights and the bizarre double-eyes of the spookfish,

Pay it forward? Cooperative behaviour spreads through a group, but so does cheating

Mon, 08 Mar 2010 15:00:59 -0500

Ever wonder if acts of kindness or malice really do ripple outwards? If you give up a seat on a train to a stranger, do they go onto "pay it forward" to others? Likewise, if you steal someone's seat, does the bad mood you engender topple over to other people like a set of malicious dominoes? We'd all probably assume that the answers to both questions were yes, but James Fowler and Nicholas Christakis think they have found experimental evidence for the contagious nature of cooperation and cheating.

The duo analysed data from an earlier psychological experiment by Ernst Fehr and Simon Gachter, where groups of four volunteers had to decide how much money to put in a public pot. For every unit they chipped in, each member would get 0.4 back. So any donations represent a loss to the donor, but a gain to the group as a whole. The best way for the group to benefit would be for everyone to put in all their money, but each individual player could do even better by putting in nothing and feeding off their peers' generosity.

This "public goods game" went on for six rounds. At the end of each one, the players were told what their other comrades did, although everyone's identities were kept secret. The groups were shuffled between rounds so that players never played with each other more than once.

Fowler and Christakis found that the volunteers' later moves were influenced by the behaviour of their fellow players. Each act of generosity by an individual influenced the other three players to also give more money themselves, and each of them influenced the people they played with later. One act became three, which became nine. Likewise, players who experienced stingy strategies were more likely to be stingy themselves.

Even though the groups swapped every time, the contagious nature of generous or miserly actions carried on for at least three degrees of separation. You can see an example of one such cascade in the diagram below. Eleni contributes some money to the public pot and her fellow player, Lucas, benefits (one degree). In the next round, Lucas himself offers money for the good of the group, which benefits Erika (two degrees), who gives more when paired with Jay in her next game (three degrees). Meanwhile, the effects of Eleni's initial charity continue to spread throughout the players as Lucas and Erika persist in their cooperation in later rounds.

Fowler and Christakis put some numbers on these effects too, to see the effect that a single unit of money could have on the network. They found that for each unit of money chipped in by other group members in one round (say, Eleni), a player (Lucas) would put in an extra 0.19 units in the next round on average. Influenced by this cascade of charity, the next player in the chain (Erika) would put in an extra 0.05 units. And rather than rebounding to being selfish, these co-operators all continued to add in more money in later games, for the entire length of the experiment.

Many studies have shown that abstract concepts like happiness or ideas can spread from person to person and it may seem intuitively obvious that this happens. But in most cases, it's not clear if people are actually influencing their peers, it they're all influenced by the same environments (like an earthquake or an economic meltdown), or if they simply choose to hang around others who think and behave like they do. But the last two explanations clearly don't apply to Fowler and Christakis's data because their players were randomly grouped.

Fowler and Christakis suggest that people tend to mimic the actions of those they played with. They could be directly imitating the actions of other players, or they could be looking out for cues that tell them the 'right' or 'normal' way of behaving. Whether it's specific actions or social norms that are spreading, the result is the same - a ripple effect that causes groups of people to act in similar ways.

In this way, small changes could spread throughout an entire group. Fowler and Christakis claim that "social contagion... may play an important role in the evolution of cooperation" since these ripples of behaviour would encourage members of a community to behave similarly to each other, a scenario that fosters cooperation. This all seems like fairly rosy support for the "pay-it-forward" philosophy but there are reasons to be cautious about the duo's optimistic take on the data.

For a start, they repeatedly acknowledge that both cooperative acts and selfish ones can spread throughout a group. Even though cooperation takes centre stage in the title of their paper and in the way the results are framed, they've really shown that social contagion can be just as harmful as it is helpful.

Their claim that ripples of behaviour could help to foster cooperation is also a bit dubious. In Fehr and Gachter's original experiment, the players only ended up cooperating with one another if they could punish cheats at a small expense to themselves. Without punishment, they soon stopped working together. But Fowler and Christakis found signs of contagious behaviour with or without punishment, which suggests that this spread has very little influence on whether people end up working together for the common good.

Benedikt Herrmann, who has done similar psychological research with people around the world, points out that the original experiments were also done with Swiss students. They may have been anonymous but they probably knew that they were playing with other students from the same university. This is important because people are more likely to cooperate with others from the same social group.

In real life, similar games with strangers might take a very different turn. In the Fehr-Gachter experiments, Herrmann says, "It might be the case that the 'spreading of cooperation' only took place because the norm that one should cooperate with strangers was already properly established." Likewise, players from other countries, with different ethics of cooperation, might react in other ways. Herrmann, says, "In Russia, [during my own experiments], I was frequently asked by participants why they should cooperate with people who they don't know and who they regard as potentially malfeasant strangers."

All in all, Fowler and Christakis have put forward some interesting evidence for the spread of good behaviour. It's certainly nice to imagine our acts of kindness reverberating among groups of strangers who we'll never meet, but whether experiments with Swiss students really reflect this reality is unclear. And with bad deeds spreading with equal vigour, it's also unclear how these ripples affect real human networks.

Reference: Fowler, J., & Christakis, N. (2010). Cooperative behavior cascades in human social networks Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.0913149107

More on cooperation: