Salamander family tree, high altitude 'flashes'
16 September 2004
Salamander family tree defies expectations
A new UC Berkeley study of the largest family of salamanders produced a genetic family tree totally inconsistent with the accepted classification, which is based primarily on physical features.
Salamanders formerly classified together because of similar characteristics, such as a tail that breaks at only one spot as opposed to anywhere when stressed, now appear not to be close relatives at all. And salamanders that go through an aquatic larval stage are scattered about on different branches instead of grouped on one limb of the tree: Apparently some salamander lineages lost the larval stage and then reacquired it again.
“For 40 years, we have had a very clear understanding of the evolutionary history of the largest family of salamanders, Plethodontidae,” said David Wake, professor of integrative biology and an expert on salamanders. “We thought they arose in Appalachian mountain streams and then diverged in a highly patterned way, sequentially abandoning larvae for direct development, gaining highly specialized, projectile tongues, et cetera.
“The results were stunningly different than what we anticipated,” he continued. “Only one of the currently recognized four major groups is supported.”
The study, published last week in the online edition of the Proceedings of the National Academy of Sciences, was conducted by Wake’s graduate student, Rachel Mueller, to understand the evolution of the Plethodontid salamanders, a family that comprises 360 species — two-thirds of the world’s 522 known species of salamander. Known for being one of few landlubbing vertebrates without lungs — they breathe through their skin — Plethodontids were thought to have originated in the Appalachians because the southern portion of that chain has the greatest diversity of species. The new family tree, constructed by comparing the mitochondrial genomes of 22 representative Plethodontid species and five others from different salamander families, offers no support for the out-of-Appalachia theory, Mueller said.
“We can infer only a North American origin,” Mueller said. “Most likely, where these species are now doesn’t relate to where they were ages ago, because the climate and geology have changed so much, and the species have moved around.”
Though results from this one family of vertebrates can’t necessarily be generalized to other families, Mueller said, “this does tell us that, when reconstructing evolutionary relationships, you have to be careful which morphological features you assume are conservative and haven’t evolved much, and which you think are likely to have changed over time.”
High-altitude ‘flashes’ may produce ozone-degrading nitrogen oxides
Photos of red sprites, blue jets, elves, and sprite halos are now flowing into Berkeley’s Space Sciences Laboratory from the first satellite instrument devoted to the study of these puzzling high-altitude lightning flashes.
All these phenomena are caused by the discharge of lightning from storm clouds into the upper atmosphere and ionosphere, which begins at an altitude of about 100 kilometers (63 miles). These discharges produce very different effects from the craggy lightning discharges to the ground. But little is known about them because they occur between 50 and 100 kilometers above the earth’s surface, too high for airplanes to study and too low for most satellites.
The Taiwanese government, however, funded an instrument called The Imager of Sprites and Upper Atmospheric Lightning (ISUAL), which was built by a collaborative team of Taiwanese, Japanese, and UC Berkeley scientists and launched aboard the Taiwanese satellite ROCSAT-2 (Republic of China Satellite 2) on May 20 of this year.
“With ISUAL, we are trying to figure out the properties of the global electrical circuit, how the lower and upper atmosphere are coupled electrically,” said Stephen Mende, a physicist at the Space Sciences Laboratory and UC Berkeley’s principal investigator for the project. “The first goal, however, is to find the global distribution of sprites and jets, and how often they occur.”
Though the discharges are not known to have any negative effect on high-flying planes, they could have an impact on atmospheric chemistry, Mende said. Electrical discharges in the atmosphere produce nitrogen oxides (NOx), one of the agents known to degrade the protective ozone layer. If low-intensity, cloud-ionosphere discharges were occurring all the time — some 1,000 electrically active thunderstorms are going on around the world at any given time — they may be producing a significant amount of nitrogen oxides.
During its expected five years of operation, the satellite, which is in a nearly polar orbit at 891 kilometers (561 miles), also will spend time looking at the nighttime auroras over the north and south poles. ROCSAT-2, launched from California’s Vandenberg Air Force Base aboard an Orbital Sciences Corp. enhanced-version Taurus XL rocket, also carries a French-built camera that looks downward with 2-meter resolution to study the ocean and land around Taiwan.
Mende’s colleagues in building the imaging camera and the spectrophotometers were Harald U. Frey, Stewart Harris, and Henry Heetderks of UC Berkeley’s Space Sciences Laboratory. The approximately $75-million satellite was funded by the National Space Program Office of Taiwan.