- Glow-in-the-Dark Shark Turned on by Hormones
- Vet School 2.0: Stick Your Hand Up a Virtual Cow Butt
- Signature of Antimatter Detected in Lightning
Posted: 06 Nov 2009 02:01 PM PST
The safe answer to how a lantern shark turns its luminescence on and off is: "Any way it wants." Now researchers have looked into the belly of the beast and found that three hormones act as on-off switches for these glow-in-the-dark sharks. It is the first discovery of hormones controlling bioluminescence in animals, the scientists report in the November 15 Journal of Experimental Biology.
In all animals investigated up to this point, luminescence is triggered by nerve cells. Finding a parallel pathway to bioluminescence — one that's controlled by hormones, not nerves — strongly supports the notion that light-emitting powers have evolved multiple times in animals, comments marine scientist Jim Gelsleichter of the University of North Florida in Jacksonville, who was not involved in the research.
The light-emitting cells in some sharks aren't connected to prominent nerve cells, and the slow onset of their glow hinted that something other than nerves were involved. Exposing patches of skin from lantern sharks to hormones and to nerve signaling molecules confirmed that hormones turn on the sharks' bluish glow.
Melatonin, which in humans is an important hormone for sleep regulation, induced a slow, long-lasting glow in the skin patches that persisted for several hours, researchers show. This light probably serves to camouflage these velvet belly lantern sharks, Etmopterus spinax, counter-illuminating them from below as they descend to darker depths of the sea, says Julien Claes, coauthor of the study with Jérôme Mallefet of the Catholic University of Louvain in Belgium.
Prolactin, which plays a major role in reproductive physiology in people, spurred a quicker shine that lasted up to an hour the scientists report. The prolactin-induced glow might be a means of communication with other sharks and potential mates, the scientists speculate. A third hormone, alpha-MSH, turns the shark's lights off. Several common nerve signaling molecules had no effect, the researchers found.
In bony fishes, nerves control luminescence and skin coloration — an "on" switch that is speedy and precise, allowing very fine-tuned control, notes Gelsleichter. A flounder, for example, that's moved from a light to a dark background quickly changes color to match the backdrop. "If you put it on a checkerboard, it would probably turn checkerboard, there's such fine nervous control and it's very quick," he says.
But in sharks and the closely related rays, hormones control skin coloration. Like luminescence, this color change is "slower and not as finely regulated," says Gelsleichter. "If you take a stingray from a light background and put him against a dark background — it will take him a little longer. He'll almost get it right."
Even if melatonin doesn't allow super fine-tuning, it's actually a very good choice for regulating light for the sharks. Known as the "dark hormone" for its role in sleep and in seasonal shifts in animal physiology and behavior, melatonin is released by the pineal gland, which receives information about the amount of light in the external environment. Many animals secrete more melatonin when the long nights of winter arrive. Similarly, whenever a shark descends it will encounter darker waters, so a hormone that already is tuned into the dark is an ideal one to co-opt for turning on light, notes Seppo Saarela of the University of Oulu in Finland.
While Claes says he is reluctant to generalize, he suspects that other bioluminescent sharks also have hormone switches in their light-producing organs, the photophores. About one in eight shark species does some kind of glowing, says Claes, and he intends to investigate other species. "It's amazing — this work just shows that bioluminescence is a very complex phenomenon. We are still really at the beginning of this story."
Posted: 06 Nov 2009 01:04 PM PST
There's nothing tidy about sticking your arm deep into a cow's backside, getting up to your elbows in warm and gooey bovine innards.
But for new vet students, there's no avoiding the procedure: To diagnose pregnancy or check for infection, you've got to reach into a cow's rectum and feel for the uterus, ovaries and stomach. Unfortunately, proper palpation is a tough skill to teach, because once your arm is buried inside a cow butt, no one can see what you're doing.
That's why veterinarian and computer scientist Sarah Baillie has created the "Haptic Cow," a virtual, touch-feedback device that mimics the feeling of real bovine anatomy, placed inside a fiberglass model of a cow's rear end.
"With this technology, students can feel something that feels like the inside of a real cow, but I or another instructor can be following their movements on a monitor," said Baillie, who teaches at the Royal Veterinary College in London. "This means we can say, 'Come back a bit or go left a bit.' It actually means you can direct them."
Not only can professors follow a student's exact movements and critique the technique, but they can also keep track of how much force is being applied. If a fledgling vet gets too rough and exceeds the number of Newtons considered safe by experienced vets, virtual Bessie will belt out a cautionary "Moo-oo!"
Baillie first came up with the idea for the virtual cow several years ago, after an injury forced her to leave veterinary practice and retrain in computer science. She'd spent years trying to teach students how to palpate cows on the farm, so when she learned about touch-feedback technology that could simulate the feel of human anatomy, she recognized a perfect opportunity to blend her two careers.
"It took me a long time to get it right," Baillie said. "It would be no underestimate to say that the code that creates the feel has been iterated on hundreds of times. But when I got it right, I knew it was right, because I've actually felt the inside of a cow many, many times."
The current model of the Haptic Cow uses a touch feedback device from SensAble Technologies, hooked up to a computer that's programmed to deliver just the right amount of force in response to a student's touch. Instructors can set up different scenarios to help students learn the difference between the soft sensation of a healthy pregnant uterus and the firmer, doughier feel of an infected animal.
The virtual cow has been incredibly successful, and it's now being used by four of the seven veterinary colleges in the United Kingdom. Baillie was recently named "Most Innovative Teacher of the Year" in the U.K. by the 2009 Times Higher Education Awards, and the organization called her project "possibly the most significant innovation in veterinary education in the past 50 years."
But Baillie's not yet content— in addition to trying to commercialize her cow for use in the United States and Canada, she's also working on a Haptic Horse and a Haptic Cat.
"It's particularly good for cats," she said, "as they have a certain limit to their tolerance."
Image: A vet student practices on the Haptic Cow, while Sarah Baillie and a real cow look on. Courtesy of Sarah Baillie/Royal Veterinary College.
Posted: 06 Nov 2009 12:25 PM PST
WASHINGTON, D.C. — Designed to scan the heavens thousands to billions of light-years beyond the solar system, the Fermi Gamma-ray Space Telescope has now recorded some more down-to-Earth signals. During its first 14 months of operation, the flying observatory has detected 17 gamma-ray flashes associated with terrestrial lightning storms.
The flashes occurred just before, during and immediately after lightning strikes, as tracked by the World Wide Lightning Location Network.
During two recent lightning storms, Fermi recorded gamma-ray emissions of a particular energy that could only have been produced by the decay of energetic positrons, the antimatter equivalent of electrons. The observations are the first of their kind for lightning storms. Michael Briggs of the University of Alabama in Huntsville announced the puzzling findings Nov. 5 at the 2009 Fermi Symposium.
It's a surprise to have found the signature of positrons during a lightning storm, Briggs said.
During lightning storms previously observed by spacecraft, energetic electrons moving toward the craft slowed down and produced gamma rays. The unusual positron signature seen by Fermi suggests that the normal orientation for an electric field associated with a lightning storm somehow reversed, Briggs said. Modelers are now working to figure out how the field reversal could have occurred. But for now, he said, the answer is up in the air.
Recording gamma-ray flashes — which have the potential to harm airplanes in storms — isn't new. The first were found by NASA's Compton Gamma-ray Observatory in the early 1990s. NASA's RHESSI satellite, which primarily looks at X-ray and gamma-ray emissions from the sun, has found some 800 terrestrial gamma-ray flashes, Briggs noted.
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