Monday, 5 October 2009

Melicope: Hawaii's export to the Pacific

Over the years, the general consensus has been that islands of the Pacific, and particularly the incredibly isolated archipelago we fondly know as Hawaii have been the passive collectors of fauna and flora that have just happened to have swum, flown, drifted, or been blown onto their fair shores. It's generally been thought to have been a one-way process, that once something has arrived there, it settles down and makes the most of their tropical paradise. Something that those of us stuck in cold climates can relate to very well -- why would you want to leave a place that is extremely amiable and is yours for the taking?

However, recent systematic research on a number of organisms is starting to shake up this tidy story somewhat. It appears that we may have underestimated the ability of these islands to send their biota elsewhere.

The particular paper sparking this post, written by Danica Harbaugh and coauthors, features the shrub Melicope. It's widely distributed across Asia and the South Pacific, but has undergone an "explosive radiation" in Hawaii, with 47 species found in the group. As usual, the authors hypothesised that all Hawaiian species had originated from a single colonisation and formed a monophyletic group restricted to the islands. Data from a number of genes were analysed, and it was found that although it does seem to be the case that all Hawaiian Melicope were derived from a single colonisation, it hasn't remained stuck in the one place. Surprisingly, their data suggested that Hawaii has exported some of their plants to the Marquesas Islands, where they have subsequently speciated.

This data adds to the body of work that suggests that Pacific biogeography is a lot more dynamic and complicated than initially suspected. It is also another example of the very intriguing connection that exists between Hawaii and the Marquesas.

Harbaugh DT, Wagner EI, Allan GJ, Zimmer EA. 2009. The Hawaiian Archipleago is a stepping stone for dispersal in the Pacific: an example from the plant genus Melicope (Rutaceae). Journal of Biogeography 36: 230-241.

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