Coconut: origin and east-west spread from Asia

That over 12 million hectares of coconut are grown across 89 tropical countries is proof enough of their geographical spread. But whether the coconuts (Cocos nucifera L.), belonged to the same genetic type or were admixtures was not known till recently. That question has been finally answered.

Two populations

According to a paper published recently in the PLoS ONE journal, coconuts have just two well defined and differentiated populations representing two separate locations where they were cultivated — the Pacific basin and the Indo-Atlantic Ocean basin. “This pattern suggests independent origins of coconut cultivation in these two world regions,” the authors state.

Earlier attempts to find their place of origin were constrained as they were based on morphology and not DNA studies. However, the current study used DNA analysis. About 1,300 coconuts from different parts of the world were collected for the study.

The authors found that coconuts of the Pacific basin (Group A) occur primarily in the region spanning Southeast Asia to the Pacific coast of America. The other group (Group B), which represents the Indo-Atlantic Ocean basin, spans from South Asia to the Caribbean (via West Africa and the New World Atlantic).

Those that contain genetic evidence of admixture occur primarily in the southwestern Indian Ocean.

The differences

In the case of the Pacific basin group, the coconuts were very likely to have been first cultivated in Southeast Asia — Philippines, Malaysia, Indonesia. In the case of the Indo-Atlantic Ocean basin group, the likely centre of first cultivation was the southern periphery of India, including Sri Lanka, the Maldives, and the Laccadives.

This shows that the first cultivation occurred in Asia and spread in both eastward and westward directions across the Pacific and Atlantic Oceans respectively.

Of the two groups, the one that spans from SE Asia to the Pacific Ocean has greater number of subgroups. And this reflects the group's greater phenotypic diversity (observable characteristics or traits such as morphology or physiology).

The group that moved westward from India is represented by a single genetic subpopulation.

Genetic diversity

The two groups represent about a third of the genetic diversity. According to Kenneth Olsen of the Washington University, St. Louis, Missouri, the one-third diversity within a single species provides conclusive evidence of the two-origin theory.

Two types

Coconuts can be broadly divided into two types based on their morphology. Those which have oblong, triangular shape with plenty of fibrous husk are called niu kafa.

The second type (niu vai) has a more rounded shape and is brightly coloured with a greater proportion of liquid endosperm.

Coconuts that spread westward are the niu kafa type, while those that spread eastward and till the Pacific Ocean are the more rounded niu vai type.

Trade routes

But the study gains importance as the study of the genetic material is in line with the well known prehistoric trade routes. The eastward movement is more likely to have happened around 2,250 years ago.

The group that moved westward from India to reach the Atlantic was after Vasco da Gama's 1498 expedition to the Indian Ocean, the authors note. These coconuts moved from India to Africa and to Brazil before finally reaching the Caribbean. It was primarily due to European introductions, they note.