Extinction by Disease
Theories for what killed off the woolly mammoth and other North American megafauna some 11,000 years ago have long focused on climate change and human hunting pressure. But in 1997 another possible culprit was proposed: hyperlethal disease introduced to the immunologically naive behemoths by dogs or vermin that accompanied humans when they arrived in the New World [see “Mammoth Kill”; SciAm, February 2001]. Now Alex D. Greenwood of Old Dominion University and his colleagues have produced the first evidence of disease-induced extinction among mammals. The team’s genetic analyses indicate that two species of rat endemic to Christmas Island in the Indian Ocean went extinct because they contracted a deadly pathogen from black rats, which arrived via the SS Hindustan in 1899. Less than a decade after the black rats landed, the endemic rats were gone. The findings appear in the November 5 PloS ONE. —Kate Wong
Cloning Mice on Ice
Too bad Christmas Island is not near the North Pole. Rats that went extinct on that island might then have left frozen remains for cloning—an idea advanced to save species [see “Cloning Noah’s Ark”; SciAm, November 2000]. In a new study scientists in Japan created healthy clones from mice preserved for 16 years at –20 degrees Celsius without chemical protection from ice. They took nuclei primarily from thawed brain cells and put them into host cells, which led to a line of embryonic stem cells from which the researchers ultimately bred 13 mice. Freezing and thawing ruptures cells and damages DNA, but the work, reported online November 3 in the Proceedings of the National Academy of Sciences USA, reveals that significant genomic information survives. Whether the success can help resurrect woolly mammoths is unclear, but it offers hope at least for smaller extinct species.
Relaxing with Hydrogen Sulfide
In the 1980s scientists discovered that nitric oxide relaxes blood vessels and is crucial in circulatory health [see “Biological Roles of Nitric Oxide”; SciAm, May 1992, and “Insights into Shock”; SciAm, February 2004]. Another simple, inorganic gas also acts as a vasodilator: hydrogen sulfide, the source of the smell of rotten eggs. Mice genetically engineered not to produce an enzyme called CSE, which makes hydrogen sulfide, lacked the gas ordinarily present in their tissues. The mice developed hypertension and did not respond well to compounds that relax vessels. Human blood vessels probably also make the gas, so the study, in the October 24 Science, could lead to novel hypertension treatments.
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Stellar Ripples
The COROT space telescope, an international effort led by France, looks for planets around other stars as well as ripples on stellar surfaces [see “Dangling a COROT”; SciAm, September 2007]. It is not disappointing researchers, who last fall announced that COROT discovered an exoplanet 20 times Jupiter’s mass, raising the question of whether the object is an enormous planet or a failed star. The telescope also observed vibrations and granulation on the surfaces of three stars—features previously studied only on the sun. Similar to seismology data on Earth, these “star quakes” reveal much about stellar interiors. In the case of the three stars, described in the October 24 Science, the oscillations were 75 percent as strong as models had predicted.
Note: This article was originally printed with the title, "Updates".
