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5 December 2013 11:26 am ,
Vol. 342 ,
Dyslexia, a learning disability that hinders reading, hasn't been associated with deficits in vision, hearing, or...
Exotic, elusive, and dangerous, snakes have fascinated humankind for millennia. They can be hard to find, yet their...
Researchers have sequenced and analyzed the first two snake genomes, which represent two evolutionary extremes. The...
Snake venoms are remarkably complex mixtures that can stun or kill prey within minutes. But more and more researchers...
At age 30, Dutch biologist Freek Vonk has built up a respectable career as a snake scientist. But in his home country,...
Since arriving on the island of Guam in the 1940s, the brown tree snake ( Boiga irregularis ) has extirpated native...
An animal rights group known as the Nonhuman Rights Project filed lawsuits in three New York courts this week in an...
Researchers have been hot on the trail of the elusive Denisovans, a type of ancient human known only by their DNA and...
- 5 December 2013 11:26 am , Vol. 342 , #6163
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Fish Eyes Don't Lie
7 September 2004 (All day)
Archerfish (Toxotes jaculatrix) are famous for an unusual talent: They can shoot down above-water insects by squirting a powerful stream of water from their mouths. This ability has puzzled scientists, though, because light refraction at the water surface distorts a prey's apparent size and location. A new study suggests that sharpshooting is something the fish learn over time, and the findings may provide clues to how animals adapt when their senses don't tell the truth.
Animals must be able to size up their prey to hunt and navigate effectively. But the apparent size also depends on the distance from the viewer, so animals have to develop ways of keeping things in perspective. For aquatic animals that hunt terrestrial prey, the refraction of light when it strikes water further complicates the matter. Yet 25-centimeter-long archerfish, which dwell in river estuaries and mangroves, manage to hit their targets while not spitting at prey that are too big to swallow. How do they do it?
Setting up a carnival booth of sorts, a team of researchers led by Stefan Schuster of the University of Freiburg in Germany constructed a target made of eight different-sized black disks that could be placed at various heights above the water surface. Inexperienced fish, which received a dead fly reward regardless of which disk they hit, often shot at disks too big to swallow. But, over 4 to 8 weeks, the researchers trained some fish to hit a specific disk regardless of its height, they report in the 7 September issue of Current Biology. This showed that the fish could learn to gauge a target's absolute size. When some of these fish were retrained to recognize another disk, they nailed it even when it was placed at heights not included in the retraining. Thus, says study co-author Samuel Rossel, archerfish can learn and apply the underlying laws of perspective. “This explains how archerfish optimally select prey,” he says. “Otherwise, they would be shooting at objects that they couldn't handle.”“These fish are much cleverer than we thought,” says Michael Land, a neuroscientist at the University of Sussex, U.K. He points out that the final experiment in particular shows that the fish have learned how to do a complex calculation rather than simply memorizing a set of relationships. “That's a hard job,” he says.