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18 | NewScientist | 9 April 2011
A VAST impact scar may lurk on the otherwise fresh face of Saturn’s moon Titan. It would be the largest such structure on the icy body, which hosts a paucity of craters compared with other moons.
Robert Brown of the University of Arizona in Tucson and colleagues spotted the roughly circular, 1800-kilometre-wide bright patch near Titan’s equator in infrared images snapped by the
Cassini spacecraft. Radar data suggest Titan’s crust is fractured in this area, as would be expected following an impact. The team conclude that a 60-kilometre impactor slammed into Titan early in its history, creating the patch (Icarus, DOI: 10.1016/ j.icarus.2011.03.018).
That would be consistent with a 2006 study that identified possible deposits left by watery
UV light helps birds feed chicks
HOW does a bird know which of its brood to feed? It just checks how much UV light they reflect.
Birds are known to see UV light, but it wasn’t known why. To find out, Jesús Avilés at the Arid Zone Research Station in Almeria, Spain, examined European rollers (Coracias garrulus) and found that the foreheads of heavier chicks reflect less UV than weaklings.
The team then weighed 84 chicks born in nest boxes near the city of Guadix. They applied either a jelly containing a UV blocking agent or just jelly to the foreheads of the chicks. Four hours later they weighed them again to find out how much they’d been fed by their parents (Behavioural Ecology and Sociobiology, DOI: 10.1007/s00265-011-1164-8).
Parents with large broods preferentially fed UV-reflective nestlings over UV-blocked ones, suggesting that they used UV to decide which mouth to feed.
Angry birds kiss and make up after a brawl
DURING a fight, ravens might kick and chase each other, but if they are close allies they make up afterwards.
Plenty of primates and other mammals reconcile after a conflict, but previously no birds were known to do so, says Orlaith Fraser of the University of Vienna in Austria.
Monitoring a group of seven captive ravens (Corvus corax), Fraser and colleague Thomas Bugnyar found that pairs of birds were likely to be more friendly to each other if they had fought each other in the previous 10 minutes. “It wasn’t just standard friendly behaviour,” Fraser says. Rather, the ravens sat touching each other, and
Crater ‘ghost’ on fresh-faced Titan flows at the southern edge of the patch: cracks left by the impact may have allowed water to erupt from Titan’s interior.
Unlike fresh craters, the interior of the patch is only slightly lower than the landscape. “It’s like the ghost of a crater,” says Brown, part of the Cassini team. Charles Wood of Wheeling Jesuit University in West Virginia, also a Cassini team member, doesn’t buy it. He says the patch could just be a chance alignment of other features.
sometimes touched their beaks together or preened each other. Ravens are not tactile like primates, so sitting in contact is a strong social signal (PLoS One, DOI: 10.1371/journal.pone.0018118).
“That’s very good evidence for reconciliation,” says Filippo Aureli of Liverpool John Moores University in the UK. Comparing animals’ typical behaviour with the behaviour they display in the minutes immediately after a fight is a “well-established method” to look for such behaviour, he adds.
Ravens that had squabbled were more likely to reconcile if they were allies. “These are valuable partners who share food and support each other in fights,” says Fraser. She and Bugnyar had already shown that ravens sometimes console group members who have lost a fight.
MOUSE stem cells have been coaxed into forming a partial eyeball, and the method may one day lead to retina transplants.
Yoshiki Sasai at the RIKEN Center for Developmental Biology in Kobe, Japan, and colleagues encouraged embryonic stem cells to develop into retinal cells, and then grew them alongside a protein matrix to promote the formation of tissue. The cells transformed into the six major types of retinal cells and spontaneously arranged themselves into a layered cup-like structure, mimicking the adult retina (Nature, DOI: 10.1038/nature09941).
In a few years it may be feasible to produce samples large enough for transplantation, Sasai says.
Stem cells grow into partial eyeball