Human mediated translocation of Pacific paper mulberry [Broussonetia papyrifera (L.) L’Hér. ex Vent. (Moraceae)]: Genetic evidence of dispersal routes in Remote Oceania

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.

A tale of textiles: Genetic characterization of historical paper mulberry barkcloth from Oceania

“…Markers Bro13, Bro15 and Bropap 2801 presented the highest number of new alleles (Table 3 and Fig 3). We also detected five alleles in textile DNA that have been identified previously in herbaria samples but that were absent in contemporary accessions (Table 3) [25], for markers Bro 08, Bro 15, Bropap 2801 and Bropap 20558. Some samples presented more than two alleles per marker (Table 3 and S5 Fig) . In order to ascertain that the new alleles detected in these textile samples did not correspond to capillary electrophoresis artifacts, a control experiment was performed.…”

“…All DNA replicates obtained from the barkcloth samples were analyzed using ten microsatellite markers, as described in the Methods section. The selected markers are those that proved to be most informative for this species, as reported previously [24,25,28]. DNA from the New Guinea barkcloth sample amplified with all markers, while DNA from the sample from the Fijian textile amplified four to five markers, and the samples from the barkcloth from the Gambier Islands amplified between six and eight markers.…”

“…Allele sizes were registered in an Excel spreadsheet, as described [24]. Alleles found in samples in this study were compared with alleles in contemporary paper mulberry and herbaria samples from our collection [25]. In order to ascertain that the new alleles detected in these textile samples did not correspond to capillary electrophoresis artifacts, a control experiment was performed.…”

“…The amplifications were performed using PCR programs of 40 cycles, with reagents and materials used exclusively for work with ancient DNA, as described by Payacán et al [24]. Samples were characterized using different molecular markers, in order to compare with contemporary plants and herbaria samples [25]. Starting material for all amplifications was DNA obtained from the protocol extraction described previously.…”

“…reconstruct the dispersion of plants and humans in Oceania [9,21,22,23,24,25]. Our previous studies of B. papyrifera plants comprised those Pacific islands where extant plants are still present or from available herbarium samples.…”