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Thoughtomics

Thoughtomics

Exploring evolution through genes, computers and history

Coconuts: not indigenous, but quite at home nevertheless

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Coconut palms on the Southern Maalhosmadulu Atoll in the Pacific.

On January 9 in 1878, the Spanish brig Providencia was en route from Cuba to Spain, but would never arrive at this destination. Although the weather was clear that day, the ship wrecked off the shores of Florida. Its cargo, 20.000 coconuts harvested on the Caribbean island of Trinidad, was scattered along the coast1.

The settlers of Florida knew an opportunity when they saw one and planted some of the stranded coconuts around their homes. The coconut palms and groves that grew from these seeds later gave Palm Beach County its name. Fifty years after the Providencia sank, a reporter of the Palm Beach Post wrote:

"From that wreck has grown the palms that line the streets and parks of Palm Beaches. [..] 20.000 coconuts provided the beginning of trees not indigenous to the area, but quite at home, nevertheless."

~ Palm Beach Post, Nov 20 1938

Not indigenous, but quite at home. This description not only fits the palms that sprang from Providencia's wreck, it's true for coconut palms around the world. Although coconut palms now adorn the coasts of tropical beaches everywhere, from the Caribbean to Madagascar and Hawaii, the tree is not a native species there. All these palms, like the palms of Palm Beach, were introduced by humans.

Coconut palms can be found on every tropical coast, although they are not native there.

Humans have always been eager to bring coconuts along on their travels, and for good reasons. Coconuts are not only a source of both food and water, different parts of the coconut palm can also be used for other purposes. Alcohol and sugar can be extracted from its sap, and cocos oil from the nut itself, for example. Today, they grow on both sides of the Atlantic and Pacific ocean. But where did this useful crop first come from?

Since coconut palms have been crossed, cultivated and transported for thousands of years, retracing the coconut's path through archaeological sources alone is difficult. The coconut's collective history has been preserved far better inside its DNA. By mapping the relatedness of coconut palms around the globe, it is possible to reconstruct the tale of their expansion. Last month, Kenneth Olsen and colleagues published a thorough analysis of coconut DNA in PLoS ONE from 1322 coconut palms around the world.

These coconuts are being dried to make copra, from which cocos oil is made

The team discovered that despite the coconut's complicated history, the underlying genetic structure of coconut populations is simple. Most coconuts belonged to one of two genetically distinct groups. One population traces back its ancestry to palms on the coasts of India, the other group descended from palms in Southeast Asia. Even palms that now grow on the other side of the world are still members of one of these two groups. Palms in Middle America are mostly of the Pacific variety, whereas Caribbean palms belong to the Indian group, for example.

Since the genetic differences between the Indian and Pacific varieties are so numerous and clear, the two lineages must have been evolving in separate directions for a long time. For this reason, Olsen's team concluded that the coconut palm was not domesticated once, but twice: in India and on the Malay Peninsula. Following the Pacific domestication, settlers would have brought the coconut to the Polynesian islands. Austronesian seafarers from the Philippines later introduced the coconut to the Pacific coast of Middle America. The coconut palms that were domesticated in India spread westwards. After they had been introduced in East Africa, Europeans brought the coconut to the Atlantic coast of Africa and later to South America.

The two lineages not only differ genetically, there are also biological differences. The fruit of the Indo-Atlantic palms are more elongated and angular compared to the rounder, Pacific fruits. In earlier theories about coconut evolution, palms bearing elongated fruits were seen as wilder plant, whereas the trees with rounder fruits were supposed to be 'more domesticated'. Since the two types of palm arose from independent domestications, this theory no longer holds. Rounder fruit did not evolve from angular fruit in a linear fashion.

These coconut fruits are of the rounder ('niu vai') type.

Of course, the evolutionary history of coconut palms is not just a matter of Indian versus Pacific coconuts. Evolution never deals in black and white. The genetic differences between both varieties are not absolute. Some coconut trees, like those on Madagascar, are genetic mixtures of the Pacific and Indian varieties. At some point the two groups must have interbred and produced offspring on the African island.

Since Madagascar is an island in the Indian Ocean, so the Indo-Atlantic heritage of Madagcasar's palms is no surprise. The Pacific ancestry is more confusing though. Coconut palms on the Seychelles, an island group just north of Madagascar, contain few traces of Pacific ancestry So how did Pacific coconuts get to Madagascar?

The answer, again, involves human migration and trade. The people of Madagascar themselves partly descend from Southeast Asian ancestors. To explain this genetic mixing of people and coconuts, geneticists and anthropologists suggest that seafarers from the Malay archipelago frequented Madagascar on their trade routes to East Africa. Perhaps some of these traders and their coconuts eventually settled in Madagascar. Arab traders could also have played a role in the dispersal of Pacific coconuts. Arabic influences on East Africa are evidenced by the spread of Islam and introduction of Asian crops in this region. The Seychelles were never part of the Malay and Arabian trade routes, which explains why these palms have no Pacific heritage.

Next time you see a coconut palm, I hope you'll realize that is more than just a fancy tree with tasty seeds on a tropical beach. The coconut's evolutionary history is intertwined with the complex history of human migration, trade and colonization. That's not bad, for a humble seed far from home, but quite at home nevertheless.

The genetic composition and spread of coconut palms around the world


Images:

Coconut palm by Sykez

Coconut distribution by Niklas Jonsson.

Drying coconuts by Dan Iserman

Golden coconut fruit by DeusXFlorida

Spread of coconuts around the world from second reference.

References:

Oyer H (2001), The wreck of the Providencia in 1878 and the naming of Palm Beach County, Vol. 29, South Florida History

Gunn BF, Baudouin L, & Olsen KM (2011). Independent Origins of Cultivated Coconut (Cocos nucifera L.) in the Old World Tropics. PloS one, 6 (6) PMID: 21731660

The views expressed are those of the author and are not necessarily those of Scientific American.

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