Abstract
As a portable source of food, water, fuel, and construction materials, the coconut (Cocos nucifera L.) played a fundamental role in human migrations and the development of civilization across the humid tropics. Here we investigated the coconut's domestication history and its population genetic structure as it relates to human dispersal patterns. A sample of 1,322 coconut accessions, representing the geographical and phenotypic diversity of the species, was examined using ten microsatellite loci. Bayesian analyses reveal two highly genetically differentiated subpopulations that correspond to the Pacific and Indo-Atlantic oceanic basins. This pattern suggests independent origins of coconut cultivation in these two world regions, with persistent population structure on a global scale despite long-term human cultivation and dispersal. Pacific coconuts show additional genetic substructure corresponding to phenotypic and geographical subgroups; moreover, the traits that are most clearly associated with selection under human cultivation (dwarf habit, self-pollination, and “niu vai” fruit morphology) arose only in the Pacific. Coconuts that show evidence of genetic admixture between the Pacific and Indo-Atlantic groups occur primarily in the southwestern Indian Ocean. This pattern is consistent with human introductions of Pacific coconuts along the ancient Austronesian trade route connecting Madagascar to Southeast Asia. Admixture in coastal east Africa may also reflect later historic Arab trading along the Indian Ocean coastline. We propose two geographical origins of coconut cultivation: island Southeast Asia and southern margins of the Indian subcontinent.
Highlights
The impact of the coconut palm (Cocos nucifera L.) on the history of human dispersal in the humid tropics is unparalleled in the plant kingdom
Genotypes were successfully obtained for 1322 samples, representing 1210 individuals from the Generation Challenge Programme (GCP)/Centre for International Development (CIRAD) collection and 112 samples from the western Indian Ocean (Table S1)
The GCP/CIRAD collection has previously been categorized into a hierarchical classification scheme based on a combination of criteria, including phenotypes, molecular markers, geographic distribution, and known introduction history [7]
Summary
The impact of the coconut palm (Cocos nucifera L.) on the history of human dispersal in the humid tropics is unparalleled in the plant kingdom. As a portable source of both food and water, the coconut played a critical role in the ability of humans to voyage, establish trade routes, and colonize lands in the Pacific Rim and regions throughout the Old World tropics [1,2]. This species continues to have hundreds of uses as a source of food, drink, fiber, construction material, charcoal, and oil (used in cooking, pharmaceuticals, industrial applications, and biofuels); over 12 million hectares of coconut are currently planted across 89 tropical countries [3]. The species is typically found in areas of present or past human activity, and all or most coconut populations worldwide have likely been influenced by human cultivation and dispersal
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