Amphibian species upend a Darwin idea

Charles Darwin has had a remarkable record over the past century, not only in the affirmation of evolution by natural selection, but in the number of his more specific ideas that have been proved correct. He may, however, have been wrong about invasive species, at least where amphibians are concerned. Darwin believed that when an invasive species entered a region where a closely related species already existed, it would most likely be unsuccessful because of a competition for resources.“Instead, we found the opposite pattern with amphibians,” said Reid Tingley, a biologist at the University of Sydney. “When frogs and toads and salamanders invade an area where a similar species exists, they are more, not less, likely to establish themselves.”

He and his colleagues report their findings in this month’s issue of The American Naturalist. This is the first study that contradicts Darwin’s invasive species hypothesis using animals.

The researchers analysed a large database containing information on amphibians that had been introduced outside of their native ranges. They studied 521 successful introductions that took place from 1696 to 2006. About 55 percent of the introductions occurred after 1900, when travel and trade began to increase.

One explanation as to why the amphibians seem to thrive when introduced in locations with related species is that there is a natural suitability. When close relatives are already doing well, it’s a positive sign, Tingley said. The amphibians studied were primarily in North America and Europe, but included species in Asia, Africa and Australia as well. The findings could help conservationists predict the risk levels of introducing specific alien species into a region.

New virus-level view of the world

Researchers report this week that they have constructed the world’s most powerful optical microscope, allowing scientists to see objects the size of a virus. The findings appear in the current issue of the journal Nature Communications. The new technology combines traditional optical microscopy with tiny particles, called transparent microspheres, that magnify images. “It’s very simple,” said Lin Li, a laser engineer at the
University of Manchester in England and one of the authors of the report. “We used small glass beads on the target surface which we want to see, and after that put it under a standard optical microscope.”

By doing so, Li and his colleagues were able to study images that were about 50 nanometers in length. The technology will allow scientists to study viruses, DNA and other molecules in real time, without the processing that more sophisticated electron and fluorescence microscopes require, he said. Still, the new technology offers significantly less power than electron microscopes, which have been around since the 1930s. The most powerful electron microscopes today can magnify a subject two million times; Li’s optical technique offers a magnification of only 6,500 times. “This is just an alternative, to provide an opportunity for scientists to study using optical microscopy,” he said. “And our system is very cheap.”