Saturday, July 19, 2014

Hawaiian koa seed made 10,300-mile voyage, 1.4 million years ago, to Réunion Island

If you as a Hawaiian resident wander into a forest on the remote island of Réunion Island, you might feel at home.

That’s because the koa trees are nearly the same genetically as the Hawaiian koa—and must have originated in the Hawaiian Islands.

That’s a remarkable thing, because it happened before humans got involved—more than a million years before. 

And it’s a significant distance—10,300 miles. Réunion is half a world and two oceans away, tucked in the west Indian Ocean between Madagascar and Mauritius.

Scientists in a paper in the journal New Phytologist report that the Acacia koa of Hawai`i and the Acacia heterophylla of Réunion are very closely related. The Hawaiian koa are older, and are the source of the Réunion trees. The authors called it “one of the most exceptional examples of such dispersal.”

Indeed, some Hawaiian and Réunion trees are even more closely related to each other than some Hawaiian koas are related to each other. Furthermore, all the Hawaiian and Réunion acacias are more closely related than any of them is to their presumed ancestral species in Australia.

Their best guess is that a koa seed from Hawaiian forests arrived on a bird’s body or in a bird’s gut at Réunion. It is unlikely to have drifted because a koa seed won’t remain viable after soaking in in salt water. 

The researchers used molecular techniques to determine that the genetic differences between the Hawaiian and Réunion acacia trees all occurred within the past 1.4 million years. That suggests that the koa seed traveled to Reunion about that long ago. 

The journal Nature reviewed the story in one of its June issues.

Citation: Relatedness defies biogeography: the tale of two island endemics (Acacia heterophylla and A. koa, Authors Johannes J. Le Roux, Dominique Strasberg, Mathieu Rouget, Clifford W. Morden, Megan Koordom, David M. Richardson. New Phytologist. First published: 18 June 2014. DOI: 10.1111/nph.12900

© Jan TenBruggencate 2014

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