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Archive for February, 2011
Fossil pits show how ammonites turned parasites into pearls
Ammonites – the ancient relatives of squid and octopuses – left behind some of the most common and beautiful fossils. But look closely at their elegant, spiral shells and you might be able to spot a sinister secret. Some of them are dotted with small pits along their inner walls. Kenneth de Baets from the University of Zurich thinks that the remains of parasitic worms that infested the ammonites and were eventually trapped and killed.
The pits were first described by Michael House in 1960 and they’re known as “Housean pits” in his honour. They’re also called “pearls” since House suggested that these precious stones once resided in the pits. We associate pearls with oysters but any shelled mollusc can produce them, from ammonites to clams. If parasites or irritating particles get inside the shell, the animal protects itself by sealing off the intruder in a mineral sphere. Pearls may be pretty but they’re also a defensive prison.
Now, de Baets, together with Christian Klug and Dieter Korn, has confirmed House’s ideas by studying a large sample of ammonite shells, which he uncovered in Morocco. He thinks that the pits were indeed once filled by pearls. These precious prisons were created to trap parasitic worms.
The critical piece of evidence was a series of thin tubes within each of the pits, which led to the shell’s outer surface. De Baets discovered these tubes by looking carefully at cross-sections of ammonite shells, and he thinks that they’re tunnels created by parasites.
Certainly, they’re not normal parts of the ammonite’s shell – you can’t find them in all specimens and they’re seldom arranged symmetrically. And they’re not the result of objects penetrating or boring through the shell from outside, because no such marks have been found. Instead, their shape and size suggest that they were created by a living thing. De Baets thinks that they’re a close match to the tubes created by modern flukes or trematodes – a group that commonly infects snails, cephalopods and other molluscs.
The trematodes could have swum through the gap between the shell and the ammonite’s body. Alternatively, they could have wormed their way towards the shell from an internal organ, after being swallowed. Once inside, they would have fed upon the host’s tissues until they were sealed in by the overgrowing shell and trapped within a pearl.
If de Baets is right, these parasites have been infecting their cephalopod hosts for around 400 million years. To understand their evolution, he compared the different types of pits and built a family tree that revealed their evolutionary relationships. The tree shows that over time, the parasites went from creating a few big pits to several, smaller ones. The tree provides a tantalising glimpse into the battles between parasite and host, with some trematodes giving up soon after infecting ammonites, others jumping from host to host and yet others co-evolving with the same partner for around 15 million years.
Studying prehistoric parasites isn’t easy. They’re usually small, they tend to live inside their hosts, and their typically soft bodies don’t fossilise well. Often, the only clues to their presence at the traces of the damage they caused. Like the Housean pits of ammonite shells, many of these signs are obscure to the untrained eye, including cysts on the surface of shells and holes created by driller-killers.
I’ve written about two of the most compelling examples, discovered in recent years. David Hughes from Harvard University claimed that small scars on the veins of fossil leaves were left behind by ants that were infected by a lethal fungus. In their deaths, the ants gripped the leaves in their jaws while the fungus fatally erupted from their heads. And Ewan Wolff from the University of Wisconsin thinks that small pits in the jaws of Tyrannosaurus rex were caused by a parasite whose relatives cause trichomonosis in modern birds. This “plague of tyrants” would have created ulcers throughout the dinosaur’s jaw and eroded its bone.
In the most exciting examples, parasites are preserved together with their hosts in mutual death throes. Witness, for example, a mite that was trapped while sucking the blood from a spider. George Poinar Jr, the scientist who popularised the Jurassic Park idea of extracting DNA from insects trapped in amber, has found several such cases. In pieces of amber, he has discovered: a sand fly whose body is riddled with a parasite similar to those that cause sleeping sickness; several parasitic worms actually bursting out of their hosts; a parasite feeding on another parasite, growing on the world’s oldest mushroom; and many more.
Reference: Klug, C. (2010). Devonian pearls and ammonoid-endoparasite co-evolution Acta Palaeontologica Polonica DOI: 10.4202/app.2010.0044
More on parasites:
- Pocket science – ancient death-grip scars
- The plague of tyrants – a common bird parasite that infected Tyrannosaurus
- Body-snatching, not socialising, drove the evolution of bigger-brained insects
- Parasitic worms paint warning colours on their hosts using glowing bacteria
- Disfiguring disease caused by an alliance between three parasites
I've got your missing links right here (27th February 2011)
Top ten picks
Ferris Jabr takes sign language at the AAAS conference and makes this wonderful piece out of it. Superb.
The story of Jonathan Joshua Foer, a journalist who trained himself for the US Memory Championship & achieved record-breaking success
Sir John Beddington, the UK’s Chief Scientific Advisor, made widely quoted comments about “intolerance” towards pseudoscience. Frank Swain and Alice Bell ask if he’s right.
This is wonderful and, I predict, will be increasingly common as interdisciplinary science becomes the norm. Kate Clancy and SciCurious tag-team a study on that time of the month, each covering their own speciality
The Templeton Foundation – friend of science, or “sneakier than the creationists”? Great feature by Mitch Waldrop. And another one by Shanta Barley, looking inside the mind of a man who was scientist by day and animal “activist” by night
If it wasn’t bad enough that few new antibiotics are in development, we’re running out of the ones we have. By Maryn Mckenna
Brian Switek discusses the convoluted family trees of horses and humans (and how it’s a problem that we have a sparse fossil record for chimps).
Behold Churnalism.com – the Media Standards Trust’s new engine for discovering PR-based shoddy journalism, with commentary from the Guardian
Are some aliens worth saving? A fascinating piece by Carl Zimmer on whether some invasive species are valuable. Meanwhile, the big guy talks about the importance and power of picking stories with “zing”, rather than those that are like “a nudibranch sprinting across the top of a kelp frond.”
Fungus loaded with scorpion toxin to fight malaria
Meet our newest potential weapon against malaria – a fungus loaded with a chemical found in scorpion venom. Metarhizium anisopliae is a parasitic fungus that infects a wide variety of insects, including the mosquitoes that spread malaria. Their spores germinate upon contact and the fungus invades the insect’s body, slowly killing it. Now, Weiguo Fang from the University of Maryland has modified the fungus to target the malaria parasites lurking inside the mosquitoes.
Fang loaded the fungus with two chemicals that attack the malaria parasite Plasmodium falciparum. The first is a protein called SM1 that prevents the parasites from attaching to the mosquito’s salivary glands. By blocking Plasmodium‘s path, SM1 stops the parasite from travelling down the mosquito’s mouthparts into the people it bites. The second chemical is scorpine – a toxic protein wielded by the emperor scorpion, which kills both bacteria and Plasmodium. This double whammy of biological weapons slashed the number of parasites in mosquito saliva by 98%.
Turtles use the Earth’s magnetic field as a global GPS
In 1996, a loggerhead turtle called Adelita swam across 9,000 miles from Mexico to Japan, crossing the entire Pacific on her way. Wallace J. Nichols tracked this epic journey with a satellite tag. But Adelita herself had no such technology at her disposal. How did she steer a route across two oceans to find her destination?
Nathan Putman has the answer. By testing hatchling turtles in a special tank, he has found that they can use the Earth’s magnetic field as their own Global Positioning System (GPS). By sensing the field, they can work out both their latitude and longitude and head in the right direction.
Is crime a virus or a beast? How metaphors shape our thoughts and decisions
In 1990, in a depressed area of Buffalo, New York, eleven schoolgirls were raped. According to George Kelling, a criminal justice scholar, eight of these incidents could have been prevented. After the third case, police knew that a serial rapist was on the loose but, even though they had a description and modus operandi, they issued no warning to local parents. They saw their job as catching the criminal rather than preventing more girls from being raped.
Kelling argued that the cops hadn’t wilfully neglected their duties. Their actions were swayed by their views of police-work, which were in turn affected by metaphors. They saw themselves as crime-fighters who trod the “thin blue line” protecting innocent civilians from criminal marauders. With this role entrenched in their minds, they saw their job as catching the rapist, even at the expense of preventing further crimes. As Kelling said, the eight Buffalo schoolgirls “were victims, though no one realized it at the time, not only of a rapist, but of a metaphor.”
As with all complex issues, crime is suffused with metaphors. One common frame portrays crime as a disease, one that plagues cities, infects communities, and spreads in epidemics or waves. Another depicts crime as a predator – criminals prey upon their victims, and they need to be hunted or caught. These aren’t just rhetorical flourishes; they’re mind-changing tools with very real consequences.
In a series of five experiments, Paul Thibodeau and Lera Boroditsky from Stanford University have shown how influential metaphors can be. They can change the way we try to solve big problems like crime. They can shift the sources that we turn to for information. They can polarise our opinions to a far greater extent than, say, our political leanings. And most of all, they do it under our noses. Writers know how powerful metaphors can be, but it seems that most of us fail to realise their influence in our everyday lives.
The Beeblebrox Illusion: scientists convince people they have three arms
“He relaxed and spread his two arms lazily across the seat back. He steered with an extra arm he’d recently fitted just beneath his right one to help improve his ski-boxing.” – Douglas Adams, The Hitchhiker’s Guide to the Galaxy
Zaphod Beeblebrox is just one of several characters from science-fiction and mythology to have extra arms. It’s a common enough trope, but would it actually work in real life? Could the human mind, which is so accustomed to controlling two arms, cope with a third or fourth one? According to Arvid Guterstam from the Karolinska Institute, the answer is yes. By placing a rubber right hand next to a person’s real one, and stroking both at the same time, Guterstam managed to convince people that they had a third arm.
Meet Diania the walking cactus, an early cousin of life's great winners
Around 520 million years ago, a walking cactus roamed the Earth. Its body had nine segments, each bearing a pair of armour-plated legs, covered in thorns. It was an animal, but one that looked more like the concoction of a bad fantasy artist. Jianni Liu from Northwest University in Xi’an discovered this bundle of spines and named it Diania cactiformis – the “walking cactus from Yunnan”. And she thinks that it sits at the roots of the most successful group of animals on the planet.
If Liu is right, Diania is one of the earliest relatives of the arthropods – the group that includes insects, spiders, crabs, and more. These species all share a segmented body, a hard external skeleton and jointed legs. They are life’s winners, the most diverse of all animal groups.
To understand what made them so special, we need to look at where they came from. “Delving around the roots of arthropods might help us understand drivers of their current huge biodiversity,” says Michael Benton from the University of Bristol. For a start, how did they evolve from soft-bodied worm-like creatures into the armoured, legged animals we know today? Diania might help to provide some answers. If Liu is right, it was an animal that was “close to the point of becoming a true arthropod”.
Drying out the cane toad invasion
In June 1935, the cane toad began its invasion of Australia. Sailors brought the animal over from Hawaii in an attempt to control the cane beetle that was ravaging Australia’s sugar cane crops. It was a mistake that the continent’s wildlife would pay for. The toad did nothing to stop the beetles. Instead, it launched its own invasion, spreading across the continent from its north-eastern point of entry. As it marched, it left plummeting populations of native species in its wake.
The toads are born conquerors. Females can lay 35,000 eggs many times a year, and each can develop into a new frog in less than 10 weeks. They’re unfussy eaters and they’ll munch away on bird eggs, smaller native frogs and more. And they have large glands behind their heads, which secrete a milky poison. Local predators (or domestic pets) that try to eat them tend to die.
Now, Daniel Florance from the University of Sydney has found a clever way of corralling the cane toad invasion. He realised that humans have continued to give the toad a hand, long after we first brought them to Australia. By creating dams and troughs, we provided the toad with watery staging grounds that allowed it to spread across otherwise impassably dry land.
Pocket Science: Stealth mode in the sea
The oceans are full of animals that seek safety in numbers, gathering together to confuse predators. But some opt for the opposite strategy.
Alexandrium is part of the sea’s collection of plankton. It’s a single-celled creature but it can create colonies by amassing together in long chains. At their most extreme, these colonies can form large swarms to produce harmful red tides.
As chains, Alexandrium swims and grows faster, but it is vulnerable to predators such as copepods – small relatives of crabs or shrimp. Erik Selander from theTechnical University of Denmark found that when the chains detect the chemical traces of copepods, they break apart. By turning back into single cells, they make themselves harder to find. They also swim at a slower pace to avoid creating telltale movements in the water. When threatened by predators, these plankton enter stealth mode.
I've got your missing links right here (19th February 2011)
Top twelve picks
The “Haworth Misadventure” is over but it seemed important to collect some links for reference, given that it was one of the more interesting things to happen this week. For those who don’t know the story, it started on Saturday when I had a spot of bother getting hold of a scientist’s contact details thanks to a none-too-helpful press officer called Aeron Haworth. I put up the email chain on my Posterous blog (including the now-infamous line “I think you have all you need for a blog”), which led to an all-out outing on Ivan Oransky’s Embargo Watch and a… er… lively comment thread. Maryn McKenna did the best job of summarising the subsequent events and collating links to the various takes (of which I’ll highlight Deborah Blum’s not least because it offers support to all science blogs and because I chuckled at the bit where she dusts off her Pulitzer and uses it as a rhetorical cosh). See also Bob’O’Hara, David Harris, MediaBistro and others. After a private and public apology on Wednesday, I accepted and drew a line underneath the matter. Subsequently, Tabitha Powledge and Charlie Petit did some post-mortems at the NASW and KJST sites. And another related story about a journalist forgetting the power of words on Twitter.
Wild animals devour an elephant in time-lapse. One hyena gets almost inside the thing!
How IBM’s Watson computer excels at Jeopardy! John Rennie explains. I bet I could take it in chess-boxing though. Meanwhile, in a case of Dr Watson meets Dr House, IBM are planning to apply Watson’s tech to medical diagnoses.
Andrea Kuszewski delivers a data smackdown on the recent “thinking-cap” paper, which claimed to produce insight with electrical stimulation. Do not miss the second half. Also on that study: thinking caps are pseudoscience masquerading as neuroscience, say a trio of scientists in the Guardian. And here’s my original take on that study
Evolution (well, mutation) in 500 lines. Wonderful.
How do you sedate a bear? Dangle a very brave man head-first into its den with syringe of tranquilizer on a pole. And you get a cool video of a snoring bear and some great data on hibernation.
Around the world in 800 days – be sure to catch up on Gaia Vince’s amazing trek across 36 countries and 5 continents, looking at the human impacts of climate change and biodiversity loss.
A great guest post by Ivan Oransky on Gary Schwitzer’s blog: why negative studies are good for health journalism & where to find them
Ooh, fascinating. Flies sniff out the difference between hydrogen and deuterium using quantum smelling. Notable because the author addresses criticisms in the comments. More coverage from New Scientist.
Rats. Wearing pants. For SCIENCE!
How wastewater stations could help to weed out illegal drug use in London’s 2012 Olympics, by Brian Mossop.
Phantom pregnancies. In men. Wonderful stuff from Emily Anthes.
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