It turns out that if you unleash giant snakes into a place that didn’t previously have giant snakes, the other local animals don’t fare so well. That seems obvious, but you might be surprised at just how badly those other animals fare.
Since 2000, Burmese pythons have been staging an increasingly successful invasion of Florida. No one knows exactly how they got there. They normally live in south-east Asia and were probably carried over by exotic wildlife traders. Once in America, they could have escaped from pet stores or shipping warehouses. Alternatively, overambitious pet owners could have released when they got too large for comfort. Either way, they seem to be thriving.
With an average length of 12 feet (4 metres), the pythons are formidable predators. They suffocate their prey with powerful coils, and they target a wide variety of mammals and birds. The endangered Key Largo woodrat and wood stork are on their menu. So are American alligators (remember this oft-emailed photo?). Conservationists are trying to halt the spread of the giant snakes, out of concern that their booming numbers could spell trouble for local wildlife.
Michael Dorcas from Davidson College thinks they are right to be concerned. In the first systematic assessment of the pythons’ impact, Dorcas has found that many of Florida’s mammals have plummeted in numbers in places where the snakes now live.
There’s something unfeasibly sinister about prions. These infectious entities are incredibly simple, but they can cause fatal and untreatable diseases like mad cow disease, CJD, and others. Prions are malformed versions of a protein called PrP. Like all other proteins, they’re made of chains of amino acids that fold into complex shapes. Prions fold incorrectly, and they encourage normal PrP to do so. These deformed proteins gather in large clumps that wreck brain tissue. Once this process begins, we have no way of stopping it. Prions are little more than bits of renegade origami, but they can bring down that most complex of biological structures – your brain.
It gets worse.
Before they spread to the brain, prions often multiply in the lymphatic system –the group of organs that includes the spleen, lymph nodes, appendix and tonsils. Vincent Béringue from the French National Institute for Agricultural Research has found that prions can hide in these tissues, turning individuals into silent carriers even if they never actually develop disease. Worse still, the spleen provides an easy entry-point for prions, allowing them to jump more easily from one species to another.
We don’t like blurry vision, and we go out of our way to correct it with glasses and contact lenses. But some animals aren’t so fussy. The jumping spider not only tolerates blurry images, it deliberately produces them.
Jumping spiders, as their name suggests, leap onto their prey from afar. They judge their jumps using the two huge (and rather beautiful) eyes on the front of their faces. And to gauge how far away their targets are, they use special retinas that produce sharp images and out-of-focus ones at the same time.
Other animals have many different ways of judging depth, but none of them apply to jumping spiders. Humans mostly rely on our two eyes. Each gets a slightly different view of the world and our brain uses these differences to triangulate the distance to objects in front of us. But this ‘binocular vision’ only works if the two eyes see overlapping parts of the world. Those of jumping spiders do not.
Chameleons can judge distance by sensing how much they have to focus their eyes to bring an object into sharp relief. But jumping spiders have no way of actively focusing their eyes. Finally, some insects judge distance by shaking their heads from side to side, which makes nearby objects move further across their field of view than far ones. But jumping spiders can accurately pounce onto their prey without moving their heads.
Without any of these three methods, how could they possibly gauge their precise killing pounces with any sort of accuracy? Takashi Nagata from Osaka City University has the answer.
Each of the front eyes has a unique staircase-shaped retina, with four layers of light-sensitive cells lying one over the other. By contast, our retinas only have one such layer. Scientists have known about the staircase retinas since the 1980s, but Nagata has finally shown exactly what they do. He found that the top two layers are most sensitive to ultraviolet light. The two on the bottom have a penchant for green.
And that’s a bit odd. The way the layers are stacked means that green light only ever focuses sharply on the bottom one (layer 1). Blue light focuses on the one above it (layer 2), but those cells aren’t sensitive to blue. Instead, they see the world in fuzzy out-of-focus green.
Nagata thinks that this fuzzy vision isn’t a bug; it’s a feature. The amount of blur depends on an object’s distance from the spider’s eye. The closer it is, the more out of focus it is on the second retina. Meanwhile the first retina always gets a sharp image. By comparing the images on both layers, the spider can gauge depth with a single unmoving eye.
To test this idea, Nagata placed Adanson’s house jumpers in a special arena where they had to leap at prey. If the arena was flooded with green light, the spiders made accurate jumps. If Nagata used red light of equal brightness, they fell short of the mark. Nagata even created a mathematical model for the spider’s eye to predict how far it would miss its jump under different wavelengths of light. The model’s predictions matched the animal’s actual behaviour.
Humans actually do something similar. We can use the blurry nature of background images to get a sense of distance, even if all other cues are removed. Indeed, photographers often use blurry backgrounds to create a greater sense of depth. But this is just one of the tricks we use to judge depth, and perhaps a minor one. For the jumping spider, it seems to be the only trick in the playbook.
Reference: Nagata, Koyanagi, Tsukamoto, Saeki, Isono, Shichida, Tokunaga, Kinoshita, Arikawa & Terakita. 2011. Depth Perception from Image Defocus in a Jumping Spider. Science http://dx.doi.org/10.1126/science.1211667
Photo by Alex Wild
The eyes have it – a tour through the stunning world of animal eyes
The two apes above might look very similar to the untrained eye, but they belong to two very different species. The one on the right is a bonobo; the one on the left is a chimpanzee. They are very closely related but the bonobo is slimmer, with a smaller skull, shorter canines and tufts of lighter fur. There are psychological differences too. Bonobos spend more time having sex, and playing with one another. They’re less sensitive to stress. They’re more sensitive to social cues. And they are far less aggressive than chimps.
Many years back, a young researcher called Brian Hare was listening to the Harvard anthropologist Richard Wrangham expound on this bizarre constellation of traits. “He was talking about how bonobos are an evolutionary puzzle,” recalls Hare. “They have all these weird traits relative to chimps and we have no idea how to explain them.”
But Hare had an idea. “I said, ‘Oh that’s like the silver foxes!’ Richard turned around and said, ‘What silver foxes?’”
I’ve now been to three iterations of ScienceOnline. In the first two, the conference was home to just 250 people. This year, it almost doubled in size to a 450-strong mob. I don’t think I was alone in wondering if the event would keep its small, intimate feel. And I certainly wasn’t alone in realising that it had.
The growth was a smart move. We got a bigger, more comfortable venue. With larger crowds, the sessions had more spark to them (essential when you’re going for the “unconference” style where panellists are there to rouse the floor, not speak to them). And despite all of that, the conference retained the same flavour it always has. It still felt more like a family reunion than an academic gathering. It was a place where old friends could shake hands for the first time. It was a place where people were surrounded by like-minded fellows with mutual passions and could. Just. Cut. Loose. As I wrote last year, “You spend four days in a mental endurance event set in a parallel universe that’s largely similar to this one, except for the fact that all conversations are interesting.”
I was trying to work out why ScienceOnline was still ScienceOnline despite being twice the size. “It’s the people, stupid,” was an obvious answer, but I think it goes a bit beyond that. I think it succeeds because Bora Zivkovic, Anton Zuiker and Karyn Traphagen have realised that you only really need three things to make a great conference.
One: rig things so that the most passionate people show up. Remember that the first batch of ScienceOnline tickets sold out in less than a minute. Only the people who really, really want to be there will be waiting at the starting line at the right moment. Those people also spend the year thinking about the sessions that they’d like to see, and through the planning wiki, they craft the programme that they want. They talk to each other online, so that little time is wasted on the actual days with small-talk and ice-breakers. You can just skip to the parts about cementing relationships and building connections.
Two: once you’ve summoned your ideal crowd, you arrange everything so that they have nothing to distract them from the business of talking to each other. You give them free powerstrips at the front desk if their laptops are dying. You provide free coffee throughout the day to stimulate weary brains. You have faultless and blisteringly fast wi-fi everywhere. You have constant shuttles from the various venues, so people can just wander into the hotel lobby in a zombie-like fugue (DAMN YOU, scio12 rooster) and somehow end up at the right place. And you ensure that most guests stay in the same place so they can continue their conversations well into the evening.
Three: you equalise everything. This seems to be an emergent property of the above elements: the unconference format, the fact that delegates plan their own programme, the familial feel of the thing. Through all this and more, ScienceOnline takes a rugged career landscape and, with one deft flick of the wrist, shakes it flat. Pulitzer winners rub elbows with recent grads. Noobs sing karaoke with award-winners on backing guitar. New York Times journalists apply temporary squid tattoos to the foreheads of the scientists they write about (Carl, I look forward to seeing the disclosure statement the next time you write about Jon’s work).
It. Was. F**king. Brilliant. We knew it would be.
Thanks to everyone who had a chat with me. You were all uniformly superb.
Long live ScienceOnline. See you all next year.
(After I recover from the total physiological collapse that happens when you spend months at a time writing in silence on a chair, and then spend four days on your feet talking continuously)
This is an updated version of an old piece, edited to include new information. Science progresses by adding new data to an ever-growing picture. Why should science writing be different?
Right from its entrance, Disneyland is designed to cast an illusion upon its visitors. The first area – Main Street – seems to stretch for miles towards the towering castle in the distance. All of this relies on visual trickery. The castle’s upper bricks and the upper levels of Main Street’s buildings are much smaller than their ground-level counterparts, making everything seem taller. The buildings are also angled towards the castle, which makes Main Street seem longer, building the anticipation of guests.
These techniques are examples of forced perspective, a trick of the eye that makes objects seem bigger or smaller, further or closer than they actually are. These illusions were used by classical architects to make their buildings seem grander, by filmmakers to make humans look like hobbits, and by photographers to create amusing shots. But humans aren’t the only animals to use forced perspective. In the forests of Australia, the male great bowerbird uses the same effect to woo his mate.
Bowerbirds are relatives of crows and jays that live in Australian and New Guinea. There are 20 or so species. In most of them, the male attracts mates by building an intricate structure called a bower, which he decorates with specially chosen objects. Some species favour blue trinkets; others collect a mishmash of flowers, fruits, insect shells and more. Surrounded by these knick-knacks, the artistic male performs an elaborate display. The females judge him on his skill as a performer, builder and decorator.
The great bowerbird’s taste for interior design seems quite Spartan compared to his relatives. He creates an avenue of sticks, around 60 centimetres long, leading up to a courtyard. The courts are decorated with gesso – a collection of gray and white objects including shells, bones and pebbles.
In the early 20th century, the world was captivated by a mathematical horse called Clever Hans. He could apparently perform basic arithmetic, keep track of a calendar and tell the time. When his owner, Wilhelm von Osten, asked him a question, Hans would answer by tapping out the correct number with his hoof.
Eventually, it was the psychologist Oskar Pfungst who debunked Hans’ extraordinary abilities. He showed that the horse was actually responding to the expectations of its human interrogators, reading subtle aspects of their posture and expressions to work out when it had tapped enough. The legend of Hans’ intellect was consigned to history. But history, as we know, has a habit of repeating itself.
For the last few decades, psychologists have been using a technique called priming. With subtle hints of words or concepts, they can trigger impressive changes in behaviour. Words of cleanliness can make people behave more morally. Words related to age can slow their bodies. Words of power sharpen our mental abilities. All of these studies have suggested that our behaviour is influenced by subtle things that lie beneath the watch of our conscious awareness.
This view could well be right, but not always in the way that psychologists believe. Stephane Doyen from the Université Libre de Bruxelles has repeated one of the classic experiments in priming and shown that, in this case at least, it’s not the words that create the effect. It’s the experimenters’ expectations.
To fans of cheesy pop music, the beat of someone else’s heart is a symbol of romantic connection. To a boa constrictor, those beats are simply a sign that it hasn’t finished killing yet.
A constricting snake like a boa or a python kills its prey by suffocation. It uses the momentum of its strike to throw coils around its victim’s body. Then, it squeezes. Every time the prey exhales, the snake squeezes a little more tightly. Soon, the victim can breathe no more.
We’ve known this for centuries but amazingly, no one has worked out how the snakes can tell when to stop constricting. Scott Boback from Dickinson College has the answer. Through its thick coils, a boa can sense the tiny heartbeats of its prey. When the heart stops, the snake starts to relax.