Thursday, 17 February 2011

Amphibious caterpillars in Hawaii

The Hawaiian Islands are renowned for their unique biota that display a number of bizarre adaptations that do not appear elsewhere in the world. Widely known examples of these include the predacious caterpillars in the genus Eupithecia, and the wekiu bug (Nysius wekiuicola) that lives on Mauna Kea eating insects that are blown to them on the wind.

Recent work by Daniel Rubinoff and Patrick Schmitz have added another example to the list: amphibious caterpillars. In a paper published in March in PNAS they describe the ecology of some recently discovered 12 currently undescribed species of the moth genus Hyposmocoma that are able to develop equally well both in and out of water. Intriguingly, a phylogenetic tree hypothesizing the evolution of these insects suggest that this amphibious trait arose independently at least four times, an unexpected result for a specialised trait such as amphibiousness.

The major driving force for the development of this unique lifestyle in Hawaii is believed to be due primarily to a lack of competition. Hawaii lacks the major aquatic insect orders of the stoneflies, mayflies and caddisflies (the latter two represented by introduced species only), leaving Hawaii's freshwater environments unexploited. Hyposmocoma has stepped into the breech.

In addition to the written paper, the authors have provided movies showing the caterpillars moving in and out of the water. They are provided as supplementary information to the paper and available on the PNAS website here and here. Unfortunately, a David Attenborough documentary this isn't. There is no informative commentary spoken with a British accent, but it is an interesting watch nonetheless.

Rubinoff D, Schmitz P. 2010. Multiple aquatic invasions by an endemic, terrestrial Hawaiian moth radiation. Proceedings of the National Academy of Sciences of the United States of America 107(13):5903-5906

Zimmerman EC. 1957. Insects of Hawaii. Volume 6, Ephemeroptera-Neuroptera-Trichoptera and Supplement to Volumes 1 to 5. University of Hawai'i Press.

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