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Aquatic invasion: Scientists find first amphibious insect species

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underwater amphibious caterpillar hawaiiSeveral new species of rare Hawaiian moth caterpillars have been discovered to be able to thrive both totally submerged and totally dry. They are the first insects to be described as fully amphibious, reported a team of researchers in a study published online March 22 in the Proceedings of the National Academy of Sciences.

This genus, Hyposmocoma, which contains more than 400 species, appears to have at least 12 species whose caterpillars can live either entirely in the water or entirely on land.

"Such a flexible amphibious ecology is previously unrecorded," wrote the study authors, who are both at the Department of Plant and Environmental Protection Sciences at the University of Hawaii (U.H.) in Honolulu. "These larvae can breathe and feed indefinitely both above and below the water’s surface."

Even aquatic caterpillar species are rare, as there are only about 75 in the order Lepidoptera, which includes moths and butterflies and contains more than 150,000 species. But these 12 amphibious caterpillar species are capable of living either in terrestrial rock crevasses (meters away from water eating lichens and dry algae) or underwater latched onto rocks in fast-moving mountain streams (where they appear to "rely on direct diffusion of oxygen through the hydrophilic skin along their abdomens," the researchers reported).

What surprised the scientists even more than this discovery was that the amphibious capability appeared in three separate lineages of the genus. After genetic sequencing of 2,243 base pairs from 216 individuals in 89 species and 12 lineages, the two researchers, led by Daniel Rubinoff, an associate professor of entomology at U.H, found that the three lines of amphibious species were separated by fully terrestrial lineages, which means that these aquatic capabilities evolved three distinct times or, conversely, that several of the other, terrestrial lineages lost the abilities independently.

"Either scenario is remarkable," noted the study authors. It would "represent the repeated acquisition or loss of a truly amphibious lifestyle not recorded anywhere else" in the insect world—and possibly elsewhere in the animal kingdom.

The genus appears to have evolved alongside the changes in the Hawaiian archipelago itself. According to the genetic analysis, the aquatic abilities likely emerged some 6.8 million years ago—even before the island of Kauai existed, and at least one amphibious clade might be 10.2 million years old.

"This research demonstrates the importance of island systems for the study of evolution," Rubinoff wrote in an email to ScientificAmerican.com. "The extreme diversification of Hyposmocoma suggests the importance not only of the right place (Hawaii), but also of the right template (the ancestor of Hyposmocoma), which was able to take advantage of the ecological opportunities provided by the Hawaiian Islands over the past 20 million years."

Image of an amphibious Hyposmocoma living underwater reattaching to a rock courtesy of P. Schmitz/Rubinoff Lab





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