SCIENCE OBSERVER
In the News
This roundup summarizes some notable recent items about
scientific research, selected from news reports compiled in
Sigma Xi’s free electronic newsletters Science in the
News Daily and Science in the News Weekly. Online:
sitn.sigmaxi.org and www.americanscientist.org/sitnweekly
Altruism on the Brain
People with heightened altruistic tendencies probably have a
greater-than-normal ability to perceive purposeful action in others
and to empathize with them. Because perception of such
“agency” in others is known to correlate with activation
of the posterior superior temporal cortex, two investigators
hypothesized that functional MRI would reveal especially large
amounts of activity in this part of the brain when an altruist
perceives the actions of another agent. Two experimental trials,
each involving about two dozen subjects, confirmed the prediction,
at least in general terms.
Tankersley, D., C. J. Stowe and S. A. Huettel. Altruism is
associated with an increased neural response to agency.
Nature Neuroscience 10:150–151 (February)
Piscine Pecking Order
Male fish of the species Astatotilapia burtoni regularly
fight with one another as rivals for territory. Those that lose in
such bouts descend the social ladder, losing their normally bright
coloration and becoming reproductively dormant. To test whether such
fish could demonstrate a form of reasoning known as transitive
inference, investigators from Stanford University placed one fish in
the central compartment of an all-glass tank and allowed it to view
pairwise clashes between a total of five rivals. The experiment was
manipulated so that the five fish on display won or lost their
battles according to a prescribed pecking order, with fish
A beating fish B, who in turn conquered fish
C, who dominated fish D, who could rough up fish
E. What these investigators found was that a spectator fish
could use its observations to discern the overall ranking. They
determined that such reasoning was going on, because when they put
the spectator in a tank that contained two other fish, the spectator
would consistently gravitate toward the weaker one, even when it had
not seen those particular two rivals in battle together. That is, it
could not draw on its memory of past bouts to determine which of the
two others it would be best to steer clear of. Instead, the fish had
to determine that using transitive inference, an ability that animal
behaviorists formerly believed that only primates, rats and birds
could boast.
Grosenick, L., T. S. Clement and R. D. Fernald. Fish can infer
social rank by observation alone. Nature
445:429–432 (January 25)
Arms and the Chimp
Investigators studying wild chimpanzees have long observed these
animals using tools for various purposes: stones to pound open nuts,
say, or thin stalks of grass to lure termites out of their mound.
But two anthropologists have now discovered that chimps also make
and use tools for hunting—an ability that was formerly thought
to be uniquely human. The epiphany came from their observation of
Senegalese chimps that fashioned branches into crude spears,
removing the smaller side branches, leaves and sometimes the bark,
and then sharpening the tips with their teeth. The chimps then
forcibly jabbed these weapons into hollow branches and trunks in an
effort to skewer anything that might be hiding inside. The
investigators observed this behavior 22 times and in one instance
saw how it served to immobilize the chimp’s prey, a bush baby
(a small noctural primate), which the hunter then extracted and ate.
Pruetz, J. D., and P. Bertolani. Savannah chimpanzees, Pan
troglodytes verus, hunt with tools. Current Biology
17:1–6 (March 6)
Clouds of Rock?
Astronomers have succeeded in probing the atmosphere of a very
distant world, extra-solar planet HD 209458b. They did so by aiming
the Spitzer Space Telescope on the planet as it was passing in front
of its parent star (which this “hot Jupiter” orbits
closely) and also while the planet was out of view behind the star.
Then, by subtracting the second set of measurements from the first,
they were able to generate a spectrum that was representative of the
planet’s searing atmosphere. One spectral peak delineated in
this way suggests that HD 209458b may be covered in clouds of
silicate material—that is, the stuff of rocks. Another
spectral feature, the astronomers tentatively suggest, may signal
the presence of polycyclic aromatic hydrocarbons.
Richardson, L. J., D. Deming, K. Horning, S. Seager and J.
Harrington. A spectrum of an extrasolar planet. Nature
445:892–895 (February 22)
Rebel
with
a Cause: Allopregnanolone
Although popular wisdom attributes the mood swings of teenagers to
raging sex hormones and the stressful psychological changes of
puberty, neuroscientists are now offering a new explanation: a brain
chemical called allopregnanolone. In adults, this stress hormone
reduces anxiety by targeting certain receptors on brain cells, but
experiments with mice suggest that it may act quite differently in
adolescents, increasing brain activity to produce a state of
heightened anxiety.
Shen, H., Q. H. Gong, C. Aoki, M. Yuan, Y. Ruderman, M. Dattilo,
K. Williams and S. S. Smith. Reversal of neurosteroid effects
at σ4β2δ
GABAA receptors triggers anxiety at puberty.
Nature Neuroscience (Published online March 11)
Ancient-Bird Biplane
A recent study of Microraptor gui, a 1-kilogram
dromaeosaur, helps to answer the question of how birds evolved their
ability to fly. This feathered creature lacked a structure called
the supracoracoideus pulley and thus could not elevate its wings. So
it probably could not take off from the ground and must have used
its wings only for gliding. What’s remarkable is that its
wings were staggered, with those attached to the feet positioned
lower and somewhat farther back, much like the arrangement found in
a typical biplane.
Chatterjee, S., and R. J. Templin. Biplane wing planform and
flight performance of the feathered dinosaur Microraptor
gui. Proceedings of the National Academy of Sciences of
the U.S.A. 104:1576–1580 (January 30)
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