Hippo Sweat as a Sunscreen?

Hippopotamuses spend their days in the blazing sun, keeping themselves cool in the water and their skin protected with mud. But researchers have found they have another layer of protection -- an antibiotic sunscreen created by a sweatlike hippo secretion.

New work by a team at Kyoto Pharmaceutical University in Japan has found that the perspiration first appears colorless and then gradually turns first red and orange, then later brown. The pigments involved in the color change are in the range of ultraviolet light, suggesting that they do play a role in keeping hippo skin from burning.

The fluid secreted is not strictly sweat, because it is produced by glands under the skin. But it also acts like sweat to control body temperature.

While the brown pigment plays a role in sun protection, the shorter-lasting red pigment has antibiotic activity as well, protecting the hippo skin from disease-causing bacteria. The researchers, whose report appeared in the journal Nature, said the pigments are unexpectedly acidic.

The pigments are not, however, likely to be found soon in sunscreen preparations. That is because the pigments are highly unstable when isolated, holding their sun-protective qualities only when suspended in hippo mucus.

-- Marc Kaufman

Carbon Dioxide Theory Doubted

Many scientists hope the rising concentration of carbon dioxide (CO2) in the atmosphere will be offset by greater growth of plants on the Earth's surface. A study in the journal Science suggests this may be wishful thinking.

Plant matter is made up largely of carbon-based molecules synthesized when plants capture CO2 from the air during the process of photosynthesis. The forests, grasslands and phytoplankton of the oceans are all huge "sinks" for carbon in the environment. If plants grow faster or bigger in the presence of more CO2, theoretically they could drain off some of the excess carbon entering the atmosphere through the burning of fossil fuels and other human activities.

A research team led by Bruce A. Hungate at Northern Arizona University studied what happened to Galactia elliottii, a vine in the bean family that grows in coastal Florida, during a seven-year experiment in which enclosed but roofless plots of land were exposed to elevated concentrations of CO2.

To accumulate carbon in the form of biomass, the vines also have to accumulate -- or "fix" -- nitrogen, another essential element in living matter. Hungate and his colleagues used nitrogen fixation as a yardstick for growth.

In the first year of the experiment, the vines doubled their nitrogen fixation -- clear evidence they were flourishing in response to the higher CO2 levels. That response fell off rapidly, however. In the past three years, the elevated CO2 levels suppressed nitrogen below normal fixation

Why did this happen?

It turns out the vines were running out of molybdenum, a trace metal captured from soil that they need for one of their nitrogen-fixing enzymes. When molybdenum became scarce, the excess CO2 became unusable.

"In a study in grasslands in Switzerland, plants ran out of phosphorus," Hungate said in an interview. "Plants require many different elements. Restriction of any one of them could restrict their ability to fix more nitrogen -- and that could limit future carbon uptake by land ecosystems."

-- David Brown

Blame Bad Hair on Frizzled Genes

Some people are born prone to bad hair days, and some are not.

New research into the characteristics of hair has found similar genes throughout the animal world that determine how neat or unruly the hair might be. The genes are in the Fz6, or "frizzled," family and are now believed to play a role in the creation of human whorls and cowlicks and other hard-to-control expressions of human hair.

A new study published last week in the Proceedings of the National Academy of Sciences examined the role of the frizzled gene family (Fz6) -- which has been studied in the fruit fly -- in mice. To better understand the gene's role in mouse hair, researchers at the Johns Hopkins School of Medicine genetically engineered mice without the Fz6 gene. The animals were healthy but had unusual hair patterns, with swirls of hair on their rear feet, the backs of their heads and their chests. Some also had ridges of hair on their heads.

The researchers were surprised to learn that, on microscope examination, the unusual hair follicles appeared normal. What makes the hair pattern unusual was the skin cells holding the hair rather than the hair root itself, suggesting that the frizzled-hair trait is actually not expressed in hair at all.

Jeremy Nathans, lead author of the study, said variations in hair patterns seem to rise from variations in the genes. "It seems that in many cases unusual and distinctive hair patterns may owe more to our inheritance than to any environmental factors."

Other recent research has found a correlation between the orientation of hair whorls on the scalp and whether a person is right- or left-handed, suggesting that the same system that patterns hair may also be involved in left-right asymmetry in the brain.

-- Marc Kaufman

A study shows hippopotamuses secrete a sweatlike fluid that creates an antibiotic sunscreen.