Chloroplast DNA insights into the phylogenetic position and anagenetic speciation of Phedimus takesimensis (Crassulaceae) on Ulleung and Dokdo Islands, Korea

Abstract

Phedimus takesimensis (Ulleungdo flat-leaved stonecrop) is endemic to Ulleung and Dokdo Islands off the east coast of the Korean Peninsula. It was suggested that P. takesimensis originated via anagenetic speciation from the continental progenitor species P. kamtchaticus or P. aizoon. However, little is known of the phylogenetic relationships and population genetic structure among species of Phedimus in the Korean Peninsula and Ulleung/Dokdo Islands. We inferred the phylogenetic relationships among congeneric species in Korea based on nuclear ribosomal DNA internal transcribed spacer and chloroplast noncoding regions. We also sampled extensively for P. takesimensis on Ulleung Island and the continental species, P. kamtschaticus and P. aizoon, to assess the genetic consequences of anagenetic speciation. We found (1) the monophyly of P. takesimensis, (2) no apparent reduction in genetic diversity in anagenetically derived P. takesimensis compared to the continental progenitor species, (3) apparent population genetic structuring of P. takesimensis, and (4) two separate colonization events for the origin of the Dokdo Island population. This study contributes to our understanding of the genetic consequences of anagenetic speciation on Ulleung Island.

Genome-Wide Single Nucleotide Polymorphism Analysis Elucidates the Evolution of Prunus takesimensis in Ulleung Island: The Genetic Consequences of Anagenetic Speciation

“…Given the abundance and wide range of P. takesimensis on the island, a single origin has not been expected due to the geographical proximity of Ulleung Island from adjacent possible source areas. However, the single origin of P. takesimensis is concordant with other anagenetically derived endemic species on Ulleung Island, such as Acer takesimense (Sapindaceae; Takayama et al, 2013 ), Acer okamotoanum (Sapindaceae; Takayama et al, 2012 ), Campanula takesimana (Campanulaceae; Cheong et al, 2020 ), Dystaenia takesimana (Apiaceae; Pfosser et al, 2005 ), and Phedimus takesimensis (Crassulaceae; Seo et al, 2020 ). Currently, a single origin is considered to be the norm for anagenetically originated endemic plants on Ulleung Island ( Seo et al, 2020 ), including P. takesimensis in the present study, although there are few exceptions with multiple origins of other endemic species, such as Rubus takesimensis (Rosaceae; Yang et al, 2019 ) and Scrophularia takesimensis (Scrophulariaceae; Gil et al, 2020 ).…”

“…However, the single origin of P. takesimensis is concordant with other anagenetically derived endemic species on Ulleung Island, such as Acer takesimense (Sapindaceae; Takayama et al, 2013 ), Acer okamotoanum (Sapindaceae; Takayama et al, 2012 ), Campanula takesimana (Campanulaceae; Cheong et al, 2020 ), Dystaenia takesimana (Apiaceae; Pfosser et al, 2005 ), and Phedimus takesimensis (Crassulaceae; Seo et al, 2020 ). Currently, a single origin is considered to be the norm for anagenetically originated endemic plants on Ulleung Island ( Seo et al, 2020 ), including P. takesimensis in the present study, although there are few exceptions with multiple origins of other endemic species, such as Rubus takesimensis (Rosaceae; Yang et al, 2019 ) and Scrophularia takesimensis (Scrophulariaceae; Gil et al, 2020 ). Therefore, P. takesimensis represents an additional endemic taxon anagenetically derived on Ulleung Island and evolved by a single introduction highly likely from a source population of P. sargentii on the southern part of the Korean Peninsula according to the ML phylogeny.…”

“…The absence of (or very weak) geographic structuring among populations of P. takesimensis across Ulleung Island is clearly confirmed by phylogenetic and population genetic structure analyses based on genome-wide SNPs, which is consistent with the expected pattern for anagenetically derived endemic species (Figures 2B, 6). Lack of spatial structure was also corroborated by the AMOVA result of maternally inherited cpDNA haplotypes, which showed much lower genetic variation among populations of P. takesimensis than other endemics, 16.30%; 69.52% for Phedimus takesimensis (Seo et al, 2020), 51.90% for Campanula takesimana (Cheong et al, 2020), and 56.86% for Rubus takesimensis (Yang et al, 2019). Gene flow through dispersal of seeds and pollen is a fundamental determinant of spatial genetic structure in natural populations of trees at different spatial scales (Roser et al, 2017).…”

“…Only a few endemic species on Ulleung Island have been investigated to determine continental progenitor species and better understand the genetic consequences of anagenetic speciation. Recently, three endemic plants, Rubus takesimensis Nakai ( Yang et al, 2019 ), Campanula takesimana Nakai ( Cheong et al, 2020 ), and Phedimus takesimensis (Nakai) ’t Hart ( Seo et al, 2020 ) have been investigated based on maternally inherited plastid DNA sequences, whereas Dystaenia takesimana (Nakai) Kitag. ( Pfosser et al, 2005 ), Acer okamotoanum Nakai ( Pfosser et al, 2002 ; Takayama et al, 2012 ), and Acer takesimense Nakai ( Pfosser et al, 2002 ; Takayama et al, 2013 ) have been previously investigated based on nuclear microsatellite and amplified fragment length polymorphism markers.…”

“…Similarly, C. takesimana is substantially less genetically diverse than its continental progenitor, C. punctata , sampled from the Korean Peninsula, but it shows significant population genetic structuring ( Cheong et al, 2020 ). Phedimus takesimensis also shows apparent genetic structuring within Ulleung Island, presumably owing to its limited seed dispersal mechanism, without apparent reduction in genetic diversity ( Seo et al, 2020 ). To further assess the evolutionary importance and emerging patterns of anagenetic speciation on oceanic islands, it is necessary to explore more diverse anagenetically derived endemic species on Ulleung Island using variable molecular markers.…”