Science  26 Jul 2013:
Vol. 341, Issue 6144, pp. 325

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  1. 'Female' Chromosome May Leave a Mark on Male Fertility

    New view of X.

    X chromosomes are not as steady and unchanging as researchers have thought them to be.


    In humans, it's the Y chromosome that makes men, men—or so researchers have thought. But now scientists suggest that the X chromosome may also play a significant role in maleness. Using a special sequencing technique, the team looked at previously undecipherable portions of the X chromosome and found that it contains scores of genes that are active only in tissue destined to become sperm, researchers reported online this week in Nature Genetics. A 50-year-old theory had predicted that X genes would be stable through time and thus be quite similar across most mammals. That proved to be the case in the majority of X chromosome genes in mice and humans—which are also expressed in both sexes. But the new study found that 144 X genes in humans and 197 in mice have evolved since mice and human lineages split 80 million years ago—and many of those genes are expressed only in male germ cells. "The finding suggests that X chromosome gene content is probably changing all the time." says Jianzhi Zhang, an evolutionary geneticist at the University of Michigan, Ann Arbor.

  2. Copycat Dogs

    Do it.

    Following a command to imitate her owner, Adila touches the cone.


    Our canine pals are capable of copying a human behavior as long as 10 minutes after it's happened, scientists report this month in Animal Cognition—something that, until this discovery, only humans and apes were known to do.

    Ádám Miklósi, a behavioral ethologist at Eötvös Loránd University in Budapest, worked with Italian dog trainer and Eötvös Loránd graduate student Claudia Fugazza to teach eight female adult pet dogs that ranged in age from 2 to 10 years old and were of various breeds. They wanted to teach the dogs not only to pay attention to a demonstrated behavior ("Do as I do") and imitate it ("Do it"), but also to wait before doing so (or "deferred imitation," considered a sophisticated cognitive skill).

    Each dog underwent 10 tests—and all the dogs, they found, were capable of deferred imitation. That, Fugazza says, suggests that dogs have declarative memory—long-term memory about facts and events that can be consciously recalled. Fugazza and Miklósi say they hope that trainers take advantage of dogs' willingness to learn by watching our actions. "They do it so naturally, because dogs are predisposed to learn socially from us," Miklósi says.

  3. East Antarctic Ice Sheet Not So Stable?


    Antarctica's Wilkes Land Subglacial Basin was ice-free during parts of the Pliocene.


    To study future melting of the Greenland and Antarctica ice sheets—and resulting rising sea levels—many scientists look to the past. Current warm temperatures and greenhouse gas levels are reminiscent of the warm Pliocene Epoch that lasted from 5.3 million to 2.6 million years ago. Some data suggest that Pliocene sea levels peaked at perhaps 22 meters higher than today.

    While satellite observations suggest that the West Antarctic Ice Sheet (WAIS) is now losing mass, the far larger East Antarctic Ice Sheet (EAIS) seems more stable. But data from the Pliocene suggest that the "stable" ice sheet may be more vulnerable to warming than thought, says Carys Cook, a doctoral student at Imperial College London.

    Cook and her colleagues studied Pliocene sediments in a core off the coast of East Antarctica that reflect continental erosion patterns as the climate warmed and cooled. They found a unique geochemical "fingerprint"—a telltale ratio of neodymium to strontium isotopes—from the now ice-covered Wilkes Subglacial Basin in East Antarctica. For those sediments to have eroded and ended up offshore during the Pliocene, the basin would have had to be exposed by ice retreat, the team reported online on 21 July in Nature Geoscience.