Butterflies' Internal Compass
Every fall, monarch butterflies fly 2,500 miles from their breeding grounds in the northeastern United States and Canada to the mountains of central Mexico. The insects are not especially strong fliers, and can easily be blown off course during their journey. So scientists have been curious exactly how they navigate.
Previous research indicated that monarchs use the sun to orient themselves. But it had been unclear what they did to stay on course on cloudy days. Now, new research shows that they have an internal magnetic compass to help them find their way.
Orley Taylor Jr. of the University of Kansas and colleagues put monarchs in special chambers in which the researchers could manipulate the magnetic field. The butterflies would fly southwest under normal conditions, northwest when the magnetic field was reversed and haphazardly when any magnetic field was blocked, the researchers found.
"These tests demonstrate that monarchs navigate by means of a magnetic compass even in the absence of celestial information," the researchers report in the Nov. 23 issue of the Proceedings of the National Academy of Sciences.
"Although monarchs use both magnetic and sun compass information to orient and navigate, the system is probably more complex," they say. "Once monarchs reach Mexico, the predominant course changes from southwest to southeast . . . suggesting that structural features or other cues are used for navigation."
Humans, Chickens and Mice
Although researchers study mice to learn more about people, it turns out that humans are more closely related to chickens than to the rodents, in at least one way.
David W. Burt of the Roslin Institute in Scotland and colleagues have been studying the large-scale organization of genes in the domestic chicken and comparing it with what is known for mice and humans.
It turns out, the researchers report in the Nov. 25 issue of Nature, that the chicken and human maps have more in common in terms of the relative location of genes on chromosomes.
Based on the surprising findings, the researchers speculate that the rodent genome has evolved faster over the past few tens of millions of years than the genome of people or mice.
Blind Man Helps Study of Color
A man who lost nearly all of his ability to see when he suffered brain damage after receiving a severe electrical shock has provided new insights into how humans perceive color.
Normal color perception in humans includes a phenomenon known as "color constancy," which allows a person to see a given color as the same under different light conditions. It requires the ability to compare the wavelength composition of light reflected from multiple colors.
Researchers at University College in London, the University of Rome in Italy and the University of Ulster in Northern Ireland studied a patient known as PB. Although he lost most of his vision in the 1985 accident, he was still able to perceive colors consciously.
During a series of tests, the researchers found that his color constancy ability was severely defective. Brain scans showed that when PB perceived color, the parts of his brain that became active were those known to have heavy concentrations of cells that respond to different wavelengths of light and not those associated with color constancy.
This shows that different aspects of color perception involve different parts of the brain, the researchers say.
"We conclude that a partly defective color system operating on its own in a severely damaged brain is able to mediate a conscious experience of color in the virtually total absence of other visual abilities," they report in the Nov. 23 issue of the Proceedings of the National Academy of Sciences.
Tenderness Test for Steaks
Agriculture Department scientists have developed a test that predicts with 94 percent accuracy whether a beef carcass will provide steaks of above-average tenderness.
The research team at the USDA's Meat Animal Research Center in Clay Center, Neb., cuts a single rib-eye steak from a carcass less than 72 hours after slaughter. The steak is cooked for four minutes and stabbed with an instrument that measures resistance. The reading enables the researchers to predict whether the meat will be "tender," "intermediate" or "tough" when it is processed 10 days later.
Team leader Mohammad Koohmaraie says the new method, even when automated, cannot yet compete in terms of cost with the imperfect current system, in which a human grader simply examines the marbled fat in a carcass. But by charging 15 cents more per pound, "you can recapture the cost," Koohmaraie says. USDA-funded studies suggest that consumers would be willing to pay up to $1.84 per pound extra for a steak labeled "tender."
A World Invisible to Humans
The world's creatures perceive their environments in many different ways. Two researchers have identified a type of shrimp that can see a world that is invisible to humans.
Justin Marshall of the University of Queensland in Australia and Joahannes Oberwinkler of the University of Groningen in the Netherlands studied a creature known as the mantis shrimp, Neogonodactylus oerstedii, which usually lives in the top waters around tropical coral reefs. The shrimp, it turns out, have at least four receptors that respond to light in the ultraviolet wavelengths, which floods their habitat.
"This finding indicates that the remarkable color-vision system in these . . . crustaceans may be unique, as befits their habitat of kaleidoscopically colorful tropical coral reefs," the researchers report in the Oct. 28 issue of Nature.