Abstract
Paper mulberry, Broussonetia papyrifera (L.) L’Hér. ex Vent. (Moraceae), a dioecious species, was transported by humans from Taiwan to the islands of Remote Oceania. Its introduction and cultivation in Remote Oceania was intentional due to its cultural importance as a fiber source for barkcloth textiles. The aim of this study was to explore the genetic diversity and structure of paper mulberry populations within Remote Oceania in order to infer dispersal patterns that may reflect past human interaction among island groups. We present the integrated analysis of 380 samples (313 contemporary and 67 herbarium specimens) collected in Near and Remote Oceania. Genetic characterization was based on a set of ten microsatellites developed for B. papyrifera and complemented with the analysis of the ribosomal internal transcribed spacer ITS-1 sequence, a sex marker and the chloroplast ndhF–rpl32 intergenic spacer. Microsatellite data identify a total of 64 genotypes, despite this being a clonally propagated crop, and show three major dispersal hubs within Remote Oceania, centered on the islands of Fiji, Tonga, and Pitcairn. Of 64 genotypes identified, 55 correspond to genotypes associated to female-sexed plants that probably descend from plants introduced by the prehistoric Austronesian-speaking voyagers. The ratio of accessions to genotypes between herbarium and contemporary samples, suggests recent loss of genetic diversity. In addition to the chloroplast haplotypes described previously, we detected two new haplotypes within Remote Oceania both originating in Taiwan. This is the first study of a commensal species to show genetic structuring within Remote Oceania. In spite of the genetic bottleneck, the presence of only one sex, a timespan of less than 5000 years, and asexual propagation of this crop in Remote Oceania, we detect genetic diversity and regional structuring. These observations suggest specific migration routes between island groups within Remote Oceania.
Highlights
The last stage of human colonization of uninhabited regions of our planet, involving the settlement of the remote islands in the Pacific Ocean, has fascinated many, from early European explorers to historians, archaeologists, and, more recently, geneticists and Pacific communities
All 277 contemporary samples from Remote Oceania were identified as female plants, with the exception of 36 plants from Hawaii that were identified as male plants
We demonstrate the existence of genetic diversity and genetic structure in paper mulberry in Remote Oceania, despite its vegetative propagation and short timespan since its introduction into the region by prehistoric Austronesian speaking colonists
Summary
The last stage of human colonization of uninhabited regions of our planet, involving the settlement of the remote islands in the Pacific Ocean, has fascinated many, from early European explorers to historians, archaeologists, and, more recently, geneticists and Pacific communities. The human settlement of this region began over 45,000 years ago with the arrival of the first populations to New Guinea, New Britain, New Ireland and the Solomon Islands [2]. This region is known as Near Oceania. The region extending to the east of the Solomon Islands, known as Remote Oceania, began to be settled much more recently [3]. Western Remote Oceania (WRO), which includes New Caledonia, Vanuatu, Fiji, Wallis, Samoa, Tonga and some of the islands of Micronesia, was settled between 3000 and 2800 years before present (BP). The islands of Eastern Remote Oceania (ERO), including the Society, Marquesas, Cook and Austral Islands, as well as the Hawaiian archipelago, New Zealand and Rapa Nui (Easter Island), were not settled until at least 1500 years later, beginning around 1000 years BP [1, 4]
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