Insects are the most diverse form of life on the planet, dominating both terrestrial and freshwater ecosystems, yet no species has a life stage able to breath, feed, and develop either continually submerged or without access to water. Such truly amphibious insects are unrecorded. In mountain streams across the Hawaiian Islands, some caterpillars in the endemic moth genus Hyposmocoma are truly amphibious. These larvae can breathe and feed indefinitely both above and below the water's surface and can mature completely submerged or dry. Remarkably, a molecular phylogeny based on 2,243 bp from both nuclear (elongation factor 1α and carbomoylphosphate synthase) and mitochondrial (cytochrome oxidase I) genes representing 216 individuals and 89 species of Hyposmocoma reveals that this amphibious lifestyle is an example of parallel evolution and has arisen from strictly terrestrial clades at least three separate times in the genus starting more than 6 million years ago, before the current high islands existed. No other terrestrial genus of animals has sponsored so many independent aquatic invasions, and no other insects are able to remain active indefinitely above and below water. Why and how Hyposmocoma, an overwhelmingly terrestrial group, repeatedly evolved unprecedented aquatic species is unclear, although there are many other evolutionary anomalies across the Hawaiian archipelago. The uniqueness of the community assemblages of Hawaii's isolated biota is likely critical in generating such evolutionary novelty because this amphibious ecology is unknown anywhere else.evolution | Hyposmocoma | molecular clock | phylogeography | amphibious A quatic and terrestrial environments present divergent challenges for all animals, particularly in their need to breathe, move, and feed. Although there are many aquatic insects that can tolerate extended periods of desiccation through aestivation or diapause (1-4) and terrestrial species that tolerate extended inundation through dormancy (5-7), there are no species known to function equally well in both underwater and dry environments for extended periods. The Hawaiian Islands are the most isolated archipelago on Earth and have fostered many unusual evolutionary novelties, particularly among the arthropods (8-11). Although Lepidoptera, with more than 150,000 described species, is one of the four most diverse orders of insect, only 0.5% of all caterpillars are truly aquatic (breathing directly from the water), and none of these aquatic species can develop out of water (12, 13). However, we report the discovery of caterpillars in the endemic Hawaiian moth genus Hyposmocoma that are previously uncharacterized and restricted to the mountains of the Hawaiian Islands (Fig. 1) and that are able to thrive in both environments indefinitely and represent the only insects able to do so.In addition to foraging and resting above and under water, the larvae may also pupate under water, entailing weeks of constant inundation (Fig. S1). As a further adaptation to living around flowing water, they w...
