Birds helped acacia trees travel 18,000km from Hawaii to Réunion Islands

Subodh Varma,TNN | Jun 20, 2014, 12.58 PM IST

NEW DELHI: Two tiny islands, 18,000 kilometers apart, have the same species of acacia trees growing on them, researchers have confirmed using genetic analysis. It is thought to be the farthest journey ever undertaken by a seed, probably carried by a bird, some 1.4 million years ago. The finding is reported in the scientific journal Nature. The researchers, led by Johannes Le Roux, a molecular ecologist at Stellenbosch University in South Africa, compared the genetic structure of acacia trees from Reunion Island in the Indian Ocean with a common Hawaiian tree called koa. It had been known that these trees are very alike each other but research by Le Roux's team has confirmed their common origin.

It is not likely that acacia seeds floated from Hawaii to Reunion because these seeds don't germinate after being soaked in saltwater, Nature reported. Also, the trees grow in the mountains not near the sea shore. Although the researchers have not been able to find any clue about how the seeds travelled such a long distance, they suspect that they were either carried in a bird's stomach or even stuck to its feet. This would make it a one off event, Nature says.

Digging into the genetic structure and the mutations (changes) in it for the trees from the two islands, the scientists found a long history of globe-trotting. The tree originated in Australia, home to the largest number of Acacia species. Some 5.1 million years ago, it became established in the Hawaiian mountains after crossing over the Pacific Ocean from Australia. Then, the seeds were carried to Reunion, 3.7 million years later. Genetic changes that occurred during that time have been found on the Reunion trees confirming the path of this long journey.

Could humans have transferred the seeds from Hawaii to Reunion? According to Nature, Le Roux has ruled out the possibility of humans transferring the seed, because the time sequence of genetic changes (called the 'molecular clock') suggests that they began long before humans arrived in Reunion. In the past 15 years, a series of such improbably long journeys have been discovered, Nature reports. These include the journey of the flat nosed monkeys from Africa to South America, probably on a raft; the transfer of sundew carnivorous plants from western Australia to Venezuela, probably by birds; the journey of colorful day geckos from Madagascar to the Andaman Islands; and the journey of Ptychadenid frog from the Congo River basin to Sao Tome and Principe Islands in the Gulf of Guinea.

http://timesofindia.indiatimes.com/home/environment/flora-fauna/Birds-helped-acacia-trees-travel-18000km-from-Hawaii-to-Runion-Islands/articleshow/36879562.cms