SCIENCE
Notebook

Monday, May 1, 2006

Wings' Time-Lapse Evolution

"What use is half a wing?"

That question was posed to Charles Darwin in 1871 by an evolution skeptic named St. George Jackson Mivart. It goes to the heart of the problem of "intermediate forms" in natural selection.

Wings did not appear all at once, ready to fly. They evolved slowly from simpler versions. Darwin's theory assumes flightless proto-wings must also have enhanced the survival of species, just as fully developed wings obviously do.

In a clever set of experiments, Kenneth P. Dial, a professor of biology at the University of Montana, and collaborators took on Mivart's question and found, in a word, that half-wings are extremely useful.

They studied chukar partridges -- birds that, like quail and pheasants, spend most of their time on the ground and are capable of short bursts of flight only. Chukar chicks can run within 12 hours of hatching. They flap their nearly naked wings soon after that. Over the next 70 days, their wings grow, feathers appear, and they learn to fly. Through that whole period, they run with wings flapping.

The Montana researchers reasoned that the two-month period between birth and adult flight is, in effect, evolution working like time-lapse photography. If they could understand how flightless wings help the growing chicks, they might understand how "half-wings" help evolving birds.

They found that chukar chicks -- and adult birds -- use their wings for something called "wing-assisted incline running."

Chukars seek higher ground when threatened. Flapping their wings increases the friction between their feet and the ground. This allows the chicks -- even when flightless -- to run up ever steeper slopes to safety. If the surface is rough enough, an adult chukar can run up a vertical wall, wing assisted.

The usefulness of changing wings is a "pathway of adaptive incremental stages that might have been exhibited by the lineage of feathered . . . dinosaurs attaining powered flight," the researchers wrote in the May issue of the journal BioScience.

-- David Brown

With Melatonin, Timing Is Key

Melatonin, which millions of people take to try to adjust to time-zone changes or night shifts, helps people sleep only if it is taken at a time when the body's natural levels of the hormone are low, according to new research.

The findings could help explain why previous studies of melatonin have produced mixed results.

Charles A. Czeisler of the Brigham and Women's Hospital in Boston and colleagues studied the sleep patterns and melatonin levels of 36 healthy young adults before and after giving them either melatonin or a placebo to see if the hormone would help them adjust to the equivalent of crossing four time zones.

Melatonin improved the volunteers' ability to sleep only when they took it during the day, when their bodies were not producing melatonin in response to exposure to light, the researchers report in today's issue of the journal Sleep.

"Melatonin enabled these participants to obtain an extra half hour of sleep when they attempted to do so during the day, at a time when they were not producing melatonin themselves," Czeisler said. "Melatonin did not help these young adults sleep at night, when their body was already producing melatonin. These findings have implications for millions of people who attempt to sleep at a time that is out of synch with the brain's internal clock."

-- Rob Stein

Signs of Resilience in Corals

Although most corals face a dire fate if the world's oceans continue to warm, some reefs appear able to survive higher water temperatures by accelerating their feeding rates, according to a study in Friday's issue of the journal Nature.

The study, by scientists at Ohio State, Brown and Villanova universities, found that the Hawaiian branching coral Montipora capitata managed to recover from bleaching associated with global warming by increasing its intake of tiny plankton. However, other species, such as Porites compressa and Porites lobata , did not.

The new findings are significant because climate change represents the greatest single threat to the future survival of coral reefs. Scientists predict that as much as 60 percent of reefs worldwide may die in the next few decades because of warmer ocean temperatures.

Once the water warms, the single-celled algae (called zooxanthellae) that live inside the corals leave, depriving them of their color and most of their food energy. However, some corals such as Montipora capitata can use small tentacles to grab passing plankton and digest them, allowing them to recover from bleaching incidents.

Andrea Grottoli, a geological sciences professor at Ohio State and the paper's lead author, said that, though scientists might be able to encourage corals "to eat a bit more," she suspects species that are more inclined to feed will do better while others will die out.

"There's a glimmer of hope that there's a resilience in corals we didn't appreciate before, but I would be reluctant to say corals are now going to survive," said Grottoli, who wrote the paper along with Brown graduate student James Palardy and Villanova postdoctoral research fellow Lisa Rodrigues. "It's still pretty grim."

-- Juliet Eilperin