Plenty of animals can live equally well in air or water. They don’t call frogs amphibians for nothing, after all. But insects — whoever heard of an amphibious insect?
Daniel Rubinoff, a biologist at the University of Hawaii, has. In a paper in The Proceedings of the National Academy of Sciences, he and a post-doctoral researcher, Patrick Schmitz, report on not one but a dozen very small caterpillars that can feed and breathe indefinitely both in and out of water. They are the first insects known to be truly amphibious.
The caterpillars are members of the moth genus Hyposmocoma that is endemic to Hawaii and has about 400 known species, almost all of which are strictly terrestrial. The amphibious ones live around rocks in Hawaii’s mountain streams. Dr. Rubinoff said he did not know why collectors had not noticed them before. “It’s almost like they closed their eyes when they crossed the streams,” he said.
The caterpillars, which build silk cases in different shapes according to the species, breathe in air like other insects, through small openings called spiracles. When under water, Dr. Rubinoff said, the caterpillars most likely obtain oxygen through diffusion across the skin.
The researchers performed genetic analyses of close to 90 Hyposmocoma species and discovered that the amphibious ones “pop up essentially unrelated to each other,” Dr. Rubinoff said. That suggests the amphibious trait evolved independently several times rather than once.
Dr. Rubinoff has an idea as to how that evolution occurred. Given Hawaii’s high rainfall, the water level in the streams these species inhabit fluctuates greatly. A caterpillar that spends its time on a river rock cannot move fast enough when the water level quickly rises and the rock becomes submerged. “If you’re a little caterpillar you’ve got to hunker down and hold on,” he said.
Henry Fountain, New York Times
__________
Full article: http://www.nytimes.com/2010/04/06/science/06obbugs.html
