Polyploidy and introgression in invasive giant knotweed (Fallopia sachalinensis) during the colonization of remote volcanic islands

Daniel Sangsoon Park,Hyosig Won,Jin Hee Park,Gauri Shankar Bhandari,Chong-Wook Park

doi:10.1038/s41598-018-34025-2

Daniel Sangsoon Park, Hyosig Won + Show 3 more

Open Access

https://doi.org/10.1038/s41598-018-34025-2

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Abstract

Invasive giant knotweed (Fallopia sachalinensis) is native to northeastern Asia. In Korea, F. sachalinensis is confined to two volcanic islands, Ullung and Dok islands, where it occurs as dodecaploids (2n = 132). We investigated the molecular variation in 104 accessions from 94 populations of F. sachalinensis and its relatives throughout their native range to elucidate the origin of these island populations. All F. sachalinensis plants on Ullung and Dok islands were uniquely dodecaploid, whereas other populations were tetraploid (2n = 44). Among the 39 cpDNA haplotypes identified, the accessions from these islands shared two unique haplotypes, and were resolved as a well-supported monophyletic clade. However, this clade was sister to a clade comprising F. japonica accessions from southwestern Japan and separated from the clade comprising F. sachalinensis from other areas; this relationship is inconsistent with morphological evidence. The monophyly of the F. sachalinensis populations on Ullung and Dok islands suggests a single colonization event. The progenitor was likely from Japan, where it possibly captured F. japonica var. japonica cpDNA via introgression. The Ullung Island populations subsequently differentiated through polyploidization and mutations post-introduction. Our results also indicate that giant knotweed in Europe and North America likely originated from northern Japan and/or Sakhalin Island.

Highlights

We examined the sequences of the chloroplast DNA regions matK, ndhF, rbcL, rbcL-accD IGS, accD, accD–psaI IGS, trnL intron, and trnL–trnF IGS from F. sachalinensis and closely related taxa in Korea, Japan, the Russian Far East, the United Kingdom, and the United States to (1) assess the molecular variation in F. sachalienensis, (2) evaluate the degree of evolutionary divergence of the Ullung Island and Dok Island populations of F. sachalinensis from others across the native range, and (3) elucidate their evolutionary origin and relationships to those in other regions
Fallopia sachalinensis individuals from Ullung Island and Dok Island examined for chromosome numbers in this study were dodecaploid with 2n = 132, confirming previous reports[2] (Fig. 2, Supplementary Table 1)
The plants in Ullung Island and Dok Island referable to F. sachalinensis are nearly indistinguishable from F. sachalinensis in other areas including Japan and Sakhalin Island

Summary

Introduction

The native range of F. sachalinensis extends from Sakhalin Island of Russia to southern Japan (Fig. 1) It is readily distinguished from the other species in the section by its robust stems and conspicuously large ovate leaves (21.3–30.3 × 12.0–18.1 cm) with acute to acuminate apices and moderately to deeply cordate bases[2]. We examined the sequences of the chloroplast DNA (cpDNA) regions matK, ndhF, rbcL, rbcL-accD IGS, accD, accD–psaI IGS, trnL intron, and trnL–trnF IGS from F. sachalinensis and closely related taxa in Korea, Japan, the Russian Far East, the United Kingdom, and the United States to (1) assess the molecular variation in F. sachalienensis, (2) evaluate the degree of evolutionary divergence of the Ullung Island and Dok Island populations of F. sachalinensis from others across the native range, and (3) elucidate their evolutionary origin and relationships to those in other regions. This study represents the most comprehensive examination of giant knotweed in its native range to date

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