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Hunting harmonically. The echolocation mechanism of a horseshoe bat (Rhinolophus phillippinensis) is so finely tuned that it can detect minute changes in sounds that echo back from the fluttering wings of its insect prey. The bats’ ability to fine-tune their call may also serve to foster the development of new species, according to Tigga Kingston, a CAS geography research associate.

Traditionally, it has been thought that new species arise when geographical barriers isolate a particular animal or plant population. According to this view, with only a limited genetic pool, certain characteristics develop more prominently in succeeding generations. Over time, the isolated population differs enough to constitute a new species.

Recent research has shown that other factors may indeed play an important role in species differentiation. Kingston is studying large-eared horseshoe bats in Southeast Asia that are diverging into three sizes despite the fact that they live next to one another.

Kingston and Stephen Rossiter, a researcher at the University of London, recorded and analyzed the echolocation calls of the three sizes of horseshoe bats.

They found that each group called at different frequencies — the large bats at 27 kHz, the medium bats at 40.5 kHz, and the small bats at 54 kHz. According to the researchers, the frequency of the sounds determines the size of the prey that can be located — the low harmonic frequency of the large bats detects large insects over long distances, but misses the small insects that are easily detected at the higher frequency produced by the small bats. In essence, the prey for each of the three sizes of bats is virtually invisible to the other two.

The researchers speculate that the different calls may also make it more likely that mating communication is heard only by members of the same group, further separating the groups genetically. These findings, says Kingston, may explain the rapid dissemination of horseshoe bat species in Southeast Asia, where some 30 species have originated in the past five million years.

This work was reported in the June 10 issue of the journal Nature.


A mass-ive new understanding. An international team of physicists recently provided new evidence that the Standard Model is incomplete. This model is used by scientists to describe the rules that govern how subatomic particles interact with one another to form larger particles, atoms, and everything else in the universe. It requires that neutrinos, one of the fundamental particles, have no mass. Recent results from the Super-Kamiokande (Super-K) experiment in Japan, however, provide precise measurements of neutrino mass, confirming earlier experiments. They also verify a distinctive pattern of neutrino oscillation.

According to James Stone, a CAS professor of physics, co–principal investigator for the Super-K collaboration, and U.S. cospokesperson for the group, the “findings show that the Standard Model needs to be modified to better explain the fundamental forces that make up all matter.”

Atmospheric neutrinos are produced by high-energy collisions of cosmic rays in Earth’s upper atmosphere and come in two “flavors” — electron and muon. Electrically neutral, they are able to pass through matter over great distances without being affected. The Super-K experiments compare the number of upward-going muon-neutrinos (those traveling through the Earth) to the number of downward-going neutrinos (those traveling from the upper atmosphere) arriving at the underground Super-K detector.

In the most recent experiment, the researchers analyzed only those neutrino “events” that had very good measurements of travel distance and neutrino energy. The data revealed a distinctive pattern of muon-neutrinos changing (or oscillating) into tau-neutrinos (a third type that is not produced in the atmosphere). According to accepted theory, oscillation can occur only if the particles have mass.

K2K, a related experiment in which a neutrino beam is generated at the Japanese National High Energy Accelerator Laboratory in Tsukuba, Japan, and directed through the Earth to the Super-K detector about 250 kilometers away, recently produced data consistent with the oscillation effects reported by Super-K researchers.

The Super-K research appeared in the August issue of Physical Review Letters.

"Research Briefs" is written by Joan Schwartz in the Office of the Provost. To read more about BU research, visit http://www.bu.edu/research.

       

15 May 2003
Boston University
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