On the horizon

Mars ice cap has enough H20 to turn the planet into 'waterworld'

The southern ice cap on Mars has long been seen as a frozen holding tank of water – enough, it seems, to cover the planet in a bath 36 feet deep, according to recent measurements by Europe's Mars Express orbiter.

The spacecraft's radar probed the ice cap to depths of up to two miles, giving the best estimate yet for the amount of water there. Although the cap contains frozen carbon dioxide as well as water, the results suggest that the cap is 90 percent frozen water, say scientists.

Despite the enormous weight of the ice cap, the crust underneath it is not depressed, as is the crust on Earth beneath enormous glaciers and ice caps. The team suspects that the lack of glacial "dimples" on Mars can be traced to a planetary crust and upper mantle that are stiffer and colder compared with Earth's. The results appear in the current issue of the journal Science.

When chickadees talk, nuthatches listen

Animals have long been observed fleeing when they detect danger signals from other species. But red-breasted nuthatches have taken this ability to new levels. They tailor their response to the "threat level" that black-capped chickadees identify – sort of a Department of Avian Security.

"[Nuthatches] can tell if a raptor represents a high or a low danger from the chickadee's alarm call," says Christopher Templeton, a researcher at the University of Washington. Chickadees use one set of calls to gather mobs of other chickadees to harass a predator. But the call varies. A lumbering great horned owl earns a less worrisome warning than a smaller, agile pygmy owl.

To test the nuthatches' language skills, Mr. Templeton placed speakers beneath trees with nuthatches, but no chickadees. The nuthatches went ballistic when the team replayed chickadee calls warning of small predators. But they were far less worked up over the large-predator warning. "That one animal had cracked the code and extracted information from another species is pretty amazing," Templeton says. The results appear in the current issue of the Proceedings of the National Academy of Sciences.

A gene pool in which only females swim

Water-loving microscopic animals known as bdelloid rotifers are presenting evolutionary biologists with a puzzle – the females appear to have evolved into 360 species without ever having a male around the house.

Typically, new species come about through interbreeding. But these tiny creatures, which have been around for at least 40 million years, come in only one gender. The females produce self-fertilized eggs that are their genetic clones. Scientists recognize that these rotifers are a diverse lot. But they suspect that the differences came from random genetic mutations during millions of years of cloning.

Researchers at Imperial College in London conducted DNA studies on these creatures and took images of their jaws. Not only did different locations around the world yield different species of these rotifers, but specimens picked from different locations on a single host organism – say, a water louse – also represented different rotifer species. The team says these creatures undergo natural selection, just like organisms that reproduce sexually.

The creatures "certainly raise questions about our understanding of evolutionary processes," says Imperial College biologist Tim Barraclough. The results appear in the current issue of the Public Library of Science – Biology.

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