Abstract
Of the two major speciation modes of endemic plants on oceanic islands, cladogenesis and anagenesis, the latter has been recently emphasized as an effective mechanism for increasing plant diversity in isolated, ecologically homogeneous insular settings. As the only flowering cherry occurring on Ulleung Island in the East Sea (concurrently known as Sea of Japan), Prunus takesimensis Nakai has been presumed to be derived through anagenetic speciation on the island. Based on morphological similarities, P. sargentii Rehder distributed in adjacent continental areas and islands has been suggested as a purported continental progenitor. However, the overall genetic complexity and resultant non-monophyly of closely related flowering cherries have hindered the determination of their phylogenetic relationships as well as the establishment of concrete continental progenitors and insular derivative relationships. Based on extensive sampling of wild flowering cherries, including P. takesimensis and P. sargentii from Ulleung Island and its adjacent areas, the current study revealed the origin and evolution of P. takesimensis using multiple molecular markers. The results of phylogenetic reconstruction and population genetic structure analyses based on single nucleotide polymorphisms detected by multiplexed inter-simple sequence repeat genotyping by sequencing (MIG-seq) and complementary cpDNA haplotypes provided evidence for (1) the monophyly of P. takesimensis; (2) clear genetic differentiation between P. takesimensis (insular derivative) and P. sargentii (continental progenitor); (3) uncertain geographic origin of P. takesimensis, but highly likely via single colonization from the source population of P. sargentii in the Korean Peninsula; (4) no significant reduction in genetic diversity in anagenetically derived insular species, i.e., P. takesimensis, compared to its continental progenitor P. sargentii; (5) no strong population genetic structuring or geographical patterns in the insular derivative species; and (6) MIG-seq method as an effective tool to elucidate the complex evolutionary history of plant groups.
Highlights
The genus Prunus comprises approximately 200 species of shrubs and trees (Rehder, 1940; Kalkman, 2004), including many economically important fruit trees as well as ornamental, medicinal, and timber species (Ingram, 1948; Elias, 1980; Zomlefer, 1994; Potter, 2011)
The species boundary of P. takesimensis was delimited at the molecular level, and more importantly, its origin could be assessed through the relationship between continental progenitors and insular derivative species suggested by the MIG-seq phylogeny
Contrary to P. takesimensis, the purported continental progenitor P. sargentii was not monophyletic; accessions collected from Jeju Island and Okayama, Japan were closely related to P. serrulata species
Summary
The genus Prunus comprises approximately 200 species of shrubs and trees (Rehder, 1940; Kalkman, 2004), including many economically important fruit trees (e.g., almonds, apricots, cherries, peaches, and plums) as well as ornamental, medicinal, and timber species (Ingram, 1948; Elias, 1980; Zomlefer, 1994; Potter, 2011). Despite its relatively small size (total area of approximately 73 km with the highest peak being 984 m above sea level), Ulleung Island is rich in flora with approximately 500 native vascular plant species, of which approximately 37 are endemic (Lee and Yang, 1981). Most of these endemic species are single representatives of diverse vascular plant families that might have derived anagenetically from continental progenitors in adjacent source areas (Sun and Stuessy, 1998)
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