SCIENCE
Notebook
Monday, January 1, 2007; Page A06
Hormone Signals Mating Season
A hormone associated with the onset of puberty in humans appears to play an important role in telling rodents whether it is the proper season to reproduce. The recently discovered hormone, called kisspeptin, is different in people and in hamsters but seems to serve a related reproductive function.
Researchers came to this conclusion after studying the Siberian hamster, which naturally reproduces in warm months with lots of light but does not mate during winterlike conditions. Male hamsters were divided into two study groups, one group living in summerlike conditions and the other exposed to much shorter periods of daylight. After eight weeks, the hamsters exposed to wintry conditions experienced sharp reductions in kisspeptin in a region of the brain that regulates reproduction and sexual behavior. The animals held in summerlike conditions had heavier testes and produced more of the sex hormone testosterone.
"We've known that hamsters turn off their reproduction as the amount of light decreases, but we haven't known how it happens -- what was switching the switch," said biologist Gregory Demas of Indiana University at Bloomington. "Now we know that kisspeptin plays an integral role with these animals and probably a wide range of others."
The study, which was published in the online version of the journal Endocrinology, was conducted by Demas and researchers at the University of California at Berkeley.
The human version of kisspeptin triggers the release of two hormones known to be important to the onset of puberty and other sexual functions. People with deficits in the receptor for kisspeptin are known to have severe reproductive difficulties.
-- Marc Kaufman
Reefs May Weaken Tsunamis
Healthy coral reefs may be able to reduce tsunamis' run-up on land by half, according to a study published in December in the journal Geophysical Research Letters.
Using computer models, three scientists -- led by a researcher who at the time was studying physics as a Princeton University undergraduate -- calculated that broad and shallow reefs are especially effective at curbing the impact of tsunamis on volcanic islands.
The authors -- former Princeton student Catherine M. Kunkel, NOAA Geophysical Fluid Dynamics Laboratory scientist Robert W. Hallberg, and Princeton geosciences and public policy professor Michael Oppenheimer -- note that reefs could not have significantly softened the blow from the 2004 Indian Ocean tsunami on Banda Aceh, Indonesia, because the waves were so large and the reefs so close to shore. But they added that "for many islands, the reef is significantly far offshore to allow significant dissipation of tsunami energy over the reef" in a computer-generated scenario.
In an interview Thursday, Oppenheimer said the healthier a reef is, the better it can limit a tsunami's reach when it hits land. According to the paper, about 30 percent of the world's reefs are seriously damaged and nearly 60 percent may die by 2030 because of factors including climate change.
