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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