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Science Digest

Monday, June 8, 2009

A Hot, Dark Arctic?

Rhino- and hippo-like beasts and other large mammals roamed the Arctic 53 million years ago in a climate that reached 70 degrees Fahrenheit, and they basked part of the year in a warm midnight sun and stayed put when the sun dropped below the horizon for months at a time, new research indicates.

Based on analyses of carbon and oxygen isotopes in the fossil teeth of three species, researchers at the University of Colorado at Boulder concluded that during the dark months, the creatures shifted their diet radically.

Their summer fare of flowering plants, leaves and aquatic vegetation gave way to twigs, leaf litter, evergreen needles and fungi during the mild winters, which probably got no colder than just above freezing.

The fossils were found on Ellesmere Island, near Greenland, which since 1975 has yielded a remarkable remains of ancient creatures such as alligators, aquatic turtles, giant tortoises, snakes and flying lemurs, one of the earliest primates. Today, the region is high arctic of tundra, permafrost, ice sheets, sparse vegetation and small mammals.

In the June issue of Geology, the researchers conclude that the ancient mammals migrated south via land bridges over millions of years as the climate cooled, a pattern that could reverse with Earth's current warming. "We are hypothesizing that lower-latitude mammals will migrate north as the temperatures warm in the coming centuries and millennia," said Jaelyn Eberle, an assistant professor at UC.

-- Nils Bruzelius

The Politics of Yuck

Conservatives have a reputation for being tough on crime and national defense, but they are likely to be squeamish when it comes to more mundane aspects of life, new research indicates.

David A. Pizarro, an assistant professor of psychology at Cornell University, and his colleagues surveyed 181 adults from four politically mixed swing states to assess their general political leanings and their propensity to be disgusted by things such as maggots, feces and vomit. Those who were more likely to be grossed out tended to be more politically conservative, the researchers report in the journal Cognition & Emotion.

To test whether disgust sensitivity was associated with specific conservative ideas, the researchers then surveyed 91 Cornell undergraduates to test how sensitive they were to being grossed out and asked about their attitudes on same-sex marriage, abortion, gun control, labor unions, tax cuts, affirmative action and other issues.

Those who were most easily disgusted were more likely to oppose same-sex marriage and abortion and were somewhat more likely to support tax cuts. But there was no link to views on other policy issues.

In another study published in the journal, Pizarro and his colleagues found that those who were most easily disgusted were more likely to react negatively to homosexual behavior, such as two men kissing.

The researchers stressed that they could not conclude with certainty that there is a causal relationship between being sensitive to disgust and being conservative:

"It might be that no simple relationship is there to be found, though it does seem unlikely that political attitudes would shift a person's general emotional disposition, particularly when it comes to disgust, a basic emotion that emerges long before individuals form political attitudes."

-- Rob Stein

Deadly Evolution

The North American short-tailed shrew and the Mexican beaded lizard don't have a lot in common. But don't tell that to their prey.

The two species, one a mammal and the other a reptile, use nearly identical toxins in their saliva to kill other small animals, which they then eat. This unusual example of "convergent evolution" was described at the Society for Molecular Biology and Evolution meeting in Iowa City last week.

The toxins are encoded in two genes, BLTX in the shrew and GTX in the lizard. Each gene is a mutated variant of a gene for a substance called kallikrein, which in turn governs the activity of another biochemical, bradykinin.

When the body releases bradykinin into the bloodstream, arteries dilate, causing blood pressure to drop. The toxins rev up this response to the point where blood pressure falls so low the victim dies of shock.

Yael T. Salzman, a postdoctoral researcher at Harvard University, showed that both BLTX and GTX create the same sort of changes on the cell receptor that processes bradykinin. The toxins expose more fully the place on cells where bradykinin is processed; they guide the incoming molecules; and they make the "active site" more flexible, speeding the reaction.

The thing is, the two toxins reach this common pathway through different mutations in the ancestral kallikrein genes each creature inherited. Death by bradykinin evolved twice.

Salzman is now comparing the genomes of both animals to those of their non-toxic relatives. Small DNA differences function as a molecular clock and may tell her which one evolved the toxin first.

-- David Brown

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