Intraspecific divergence in a coastal plant, Euphorbia jolkinii, at a major biogeographic boundary in East Asia.

PREMISE: Quaternary climatic fluctuations and long-distance seed dispersal across the sea are critical factors affecting the distribution of coastal plants, but the spatiotemporal nature of population expansion and distribution change of East Asian coastal plants during this period are rarely examined. To explore this process, we investigated the genome-wide phylogenetic patterns of Euphorbia jolkinii Boiss. (Euphorbiaceae), which grows widely on littoral areas of Japan, Korea, and Taiwan. METHODS: We used plastome sequences and genome-wide single nucleotide polymorphisms in samples across the species range to reveal phylogeographic patterns and spatiotemporal distributional changes. We conducted ecological niche modeling for the present and the last glacial maximum (LGM). RESULTS: Genetic differentiation was observed between the northern and southern populations of E. jolkinii, separated by the major biogeographic boundary, the Tokara Gap. These two groups of populations differentiated during the glacial period and subsequently intermingled in the intermorainic areas of the central Ryukyu Islands after the LGM. Ecological niche models suggested that the potential range of E. jolkinii was restricted to southern Kyushu; however, it was widespread in the southern Ryukyu Islands and Taiwan during the LGM. CONCLUSIONS: This study provides evidence of genetic differentiation among coastal plant populations separated by the prominent biogeographical boundary. Although coastal plants are typically expected to maintain population connectivity through sea-drifted seed dispersal, our findings suggest that genetic differences may arise because of a combination of limited gene flow and changes in climate during the glacial period.

Molecular phylogenetic assessment of Spirobranchus kraussii-complex (Annelida: Serpulidae) from the Japanese Archipelago.

Spirobranchus kraussii (Annelida: Serpulidae) was recognized as being widely distributed both in the Pacific and Atlantic Oceans. However, the sampling records far from its type locality (South Africa) have been questioned. Actually, recent molecular phylogenetic studies showed that S. kraussii contains genetically distinct species. In this study, we performed molecular phylogenetic analyses of S. cf. kraussii collected from Japan using the nucleotide sequences of a mitochondrial gene and two nuclear genes. Three lineages were recovered within Spirobranchus kraussii-complex in Japan, and one (Spirobranchus sp. 6) showed moderate genetic difference (approximately 4%) in the mitochondrial cytb gene sequence from Spirobranchus sp. 1, an undescribed sequenced species from Honshu Island, Japan. However, the nucleotide sequences of the 18S rRNA gene and ITS2 region were nearly indistinguishable. The other lineage was clearly distinct from the other previously sequenced species and is thus considered to be another distinct species of this species complex (Spirobranchus sp. 5). Although detailed morphological assessment of these lineages is necessary to define their taxonomic status, the present study provided further implications for the species diversity within the S. kraussii-complex.