Coconut Tells Tale of Prehistoric Trade
A tall coconut with niu kafa fruit. The meat of these coconuts, called copra, is often dried, ground and pressed for oil, and their fiber is spun into rope, or coir. Credit: Wikipedia Commons.
The coconut (the fruit of the palm Cocos nucifera) is the Swiss Army knife of the plant kingdom; in one neat package, it provides a high-calorie food, potable water, fiber that can be spun into rope and a hard shell that can be turned into charcoal. What’s more, until it is needed for some other purpose, it serves as a handy flotation device.
So extensively is the history of the coconut interwoven with the history of people traveling that Kenneth Olsen, a plant evolutionary biologist from the Washington Univ. in St. Louis, didn’t expect to find much geographical structure to coconut genetics when he and his colleagues set out to examine the DNA of more than 1300 coconuts from all over the world.
"I thought it would be mostly a mish-mash," he says, "thoroughly homogenized by humans schlepping coconuts with them on their travels."
He was in for a surprise. It turned out that there are two clearly differentiated populations of coconuts, a finding that strongly suggests the coconut was brought under cultivation in two separate locations, one in the Pacific basin and the other in the Indian Ocean basin. What’s more, coconut genetics also preserve a record of prehistoric trade routes and of the colonization of the Americas.
The discoveries of the team, which included Bee Gunn, now of the Australian National Univ. in Australia, and Luc Baudouin of the Centre International de Recherches en Agronomie pour le Développement (CIRAD) in Montpellier, France, as well as Olsen, are described in an online issue of PLoS One.
The most striking finding of the new DNA analysis is that the Pacific and Indian Ocean coconuts are quite distinct genetically. "About a third of the total genetic diversity can be partitioned between two groups that correspond to the Indian Ocean and the Pacific Ocean," says Olsen.
"That’s a very high level of differentiation within a single species and provides pretty conclusive evidence that there were two origins of cultivation of the coconut," he says.
In the Pacific, coconuts were likely first cultivated in island Southeast Asia, meaning the Philippines, Malaysia, Indonesia and perhaps the continent as well. In the Indian Ocean, the likely center of cultivation was the southern periphery of India, including Sri Lanka, the Maldives and the Laccadives.
The definitive domestication traits — the dwarf habit, self-pollination and niu vai fruits — arose only in the Pacific, however, and then only in a small subset of Pacific coconuts, which is why Olsen speaks of origins of cultivation rather than of domestication.
Did it float or was it carried?
One exception to the general Pacific/Indian Ocean split is the western Indian Ocean, specifically Madagascar and the Comoros Islands, where Gunn had collected. The coconuts there are a genetic mixture of the Indian Ocean type and the Pacific type.
Olsen and his colleagues believe the Pacific coconuts were introduced to the Indian Ocean a couple of thousand years ago by ancient Austronesians establishing trade routes connecting Southeast Asia to Madagascar and coastal east Africa.
Olsen points out that no genetic admixture is found in the more northerly Seychelles, which fall outside the trade route. He adds that a recent study of rice varieties found in Madagascar shows there is a similar mixing of the japonica and indica rice varieties from Southeast Asia and India.
To add to the historical shiver, the descendants of the people who brought the coconuts and rice are still living in Madagascar. The present-day inhabitants of the Madagascar highlands are descendants of the ancient Austronesians, Olsen says.
Source: Washington Univ. in St. Louis