Some 250,000 acres of salt marsh in the southeastern United States died off between 1999 and 2003, a result of a three-year drought. Or so scientists thought. Now a new study points to another culprit that may have played a role in marsh loss: the periwinkle snail. A team led by a University of Florida ecologist, Brian Silliman, examined 12 marshes in Louisiana, Georgia, and South Carolina and found billions of periwinkle snails snacking on the fungus that attacks drought-damaged grass. To their surprise, they also discovered that once the drought-stressed grass is gone, the snails move on to healthy grass, injuring it so that fungus can attack it. The snails then eat the fungus, and the grass dies. To get a better idea of the snails' impact, the scientists simulated the effects of a drought with and without snails present. Without snails, grass growth was reduced by 45 percent. With snails, growth was reduced by 85 percent.
BOTTOM LINE: Snails compound the damage of drought. Similar interactions probably exist in other environmental systems as well, Silliman said, and could magnify the impact of global climate change.
CAUTIONS: Although the scientists' simulations suggest that the drought-snail interaction severely affects cord grass growth, they began studying the marshes about a year after the die-off was reported. It's impossible to know just how much damage the snails may have caused.
WHAT'S NEXT: Silliman plans to study how the abundance and distribution of the snails' predators, namely the overfished blue crab, affects the snails' population.
WHERE TO FIND IT: Science, Dec. 16, 2005
KELLI WHITLOCK BURTON
Americas settled by two groups, not one, study says
A new study by Brazilian scientists suggests that the New World was settled by two distinct populations, not one, as scientists previously thought. The theory that the Americas were colonized by one group 13,000 to 14,000 years ago is based largely on cranial structure. Ancient and modern Native Americans tend to exhibit features similar to ancient and modern Mongols, Chinese, Japanese, and other Northern Asians, with wide craniums, broad faces, and narrow eyes and noses. But a new analysis of the largest collection of early American remains points to another possibility. Walter Neves and Mark Hubbe of the Laboratory for Human Evolutionary Studies at the Universidade de São Paulo examined 81 skulls found in central Brazil, ranging from 7,500 to 11,000 years old. The skulls more closely resembled the cranial structure of present Australians, Melanesians, and Africans, with narrow craniums, projected lower jaws, and broad noses and eyes.
BOTTOM LINE: ''Our findings show that the occupation of the Americas is much more complex than thought," Neves said. ''Two very different human stocks entered the continent, and not just one of Mongoloid nature, as assumed."
CAUTIONS: Some scientists maintain that the difference in cranial structure could have been caused by localized evolution rather than a second group of migrants.
WHAT'S NEXT: The scientists want to create a more detailed picture of changes over time.
WHERE TO FIND IT: Proceedings of the National Academy of Sciences, Dec. 20, 2005
KELLI WHITLOCK BURTON
Your sibling's health may be crucial to your own
Having a parent with heart problems has long been known to be an important risk factor for cardiovascular disease. Now, a study suggests that having a sibling with cardiovascular disease may be at least as important. Researchers compared the rates of heart disease between almost 1,000 subjects in Massachusetts who had a sibling with cardiovascular disease and almost 5,000 subjects who did not. They found that having a sibling with cardiovascular disease raises the risk of developing heart disease by about 50 percent -- even after controlling for other known risk factors, such as high blood pressure, high cholesterol, and smoking. The risk was at least as high as that for study subjects who have a parent with cardiovascular disease.
BOTTOM LINE: If your brother or sister has heart problems, you are at higher risk for them as well.
CAUTIONS: The overwhelming majority of subjects in the study were white; the results might be different among other races. Also, although the researchers controlled for many of the known risk factors for heart disease, they may not have taken every possibility into account.
WHAT'S NEXT: More research is needed to determine why heart disease runs in families. Is it due to genetic or environmental factors?
WHERE TO FIND IT: Journal of the American Medical Association, Dec. 28, 2005
MICHAEL E. HOCHMAN