Origin of populations of Portulaca oleracea on Nishinoshima, an active volcanic oceanic island

Abstract

Nishinoshima Island, located in the Ogasawara Islands of southern Japan, underwent major volcanic eruptions in 2013, which destroyed nearly all its vegetation. Understanding the origin and characteristics of the plant populations on Nishinoshima provides valuable insights into early stages of island ecosystem development. In this study, we analysed Portulaca oleracea samples collected from Nishinoshima in 2019, before subsequent eruptions eradicated the island’s populations. Phylogenetic and population genetic analyses of plastome sequences and genome-wide single-nucleotide polymorphisms (SNPs) were performed to compare Nishinoshima samples with those from Japan and Guam. The plastome phylogeny identified five distinct lineages across Japan and Guam, two of which were present in the Ogasawara Islands (Chichijima and Hahajima Islands), with one shared between Nishinoshima and Chichijima. Genome-wide SNP analysis revealed two major genetic groups in Japan: one in the northern and another in the southern regions, including the Ogasawara Islands. The Nishinoshima populations belonged to the southern group but exhibited unique genetic characteristics, as shown by network and STRUCTURE analyses. These characteristics are likely due to limited seed dispersal, a founder effect, and genetic bottlenecks resulting from natural disturbance such as volcanic eruptions and typhoons. These findings suggest that P. oleracea on Nishinoshima is genetically close to Chichijima populations but has accumulated distinct mutations. This study provides the first genetic evidence of plant origins on Nishinoshima and contributes to understanding the dynamics of ecosystem development on newly formed oceanic islands.