Phylogeographic Analysis and Genetic Structure of an Endemic Sino-Japanese Disjunctive Genus Diabelia (Caprifoliaceae)

Abstract

The Sino-Japanese Floristic Region (SJFR) is a key area for plant phylogeographical research, due to its very high species diversity and disjunct distributions of a large number of species and genera. At present, the root cause and temporal origin of the discontinuous distribution of many plants in the Sino-Japanese flora are still unclear. Diabelia (Caprifoliaceae; Linnaeoideae) is a genus endemic to Asia, mostly in Japan, but two recent discoveries in China raised questions over the role of the East China Sea (ECS) in these species' disjunctions. Chloroplast DNA sequence data were generated from 402 population samples for two regions ( rpl 32- trn L, and trn H- psb A) and 11 nuclear microsatellite loci were screened for 549 individuals. Haplotype, population-level structure, combined analyses of ecological niche modeling, and reconstruction of ancestral state in phylogenies were also performed. During the Last Glacial Maximum (LGM) period after the Tertiary, Diabelia was potentially widely distributed in southeastern China, the continental shelf of the East China Sea and Japan (excluding Hokkaido). After LGM, all populations in China have disappeared except those in Zhejiang which may represent a Glacial refuge. Populations of Diabelia in Japan have not experienced significant bottleneck effects, and populations have maintained a relatively stable state. The observed discontinuous distribution of Diabelia species between China and Japan are interpreted as the result of relatively ancient divergence. The phylogenetic tree of chloroplast fragments shows the characteristics of multi-origin evolution (except for D. sanguinea ). STRUCTURE analysis of nuclear Simple Sequence Repeat (nSSR) showed that the plants of the Diabelia were divided into five gene pools: D. serrata, D. spathulata, D. sanguinea, D. ionostachya ( D. spathulata var. spathulata -Korea), and populations of D. ionostachya var. ionostachya in Yamagata prefecture, northern Japan. Molecular evidence provides new insights of Diabelia into biogeography, a potential glacial refuge, and population-level genetic structure within species. In the process of species differentiation, ECS acts as a corridor for two-way migration of animals and plants between China and Japan during glacial maxima, providing the possibility of secondary contact for discontinuously distributed species between China and Japan, or as a filter (creating isolation) during glacial minima. The influence of the ECS in speciation and biogeography of Diabelia in the Tertiary remains unresolved in this study. Understanding origins, evolutionary histories, and speciation will provide a framework for the...

A Narrow Endemic or a Species Showing Disjunct Distribution? Studies on Meehania montis-koyae Ohwi (Lamiaceae)

“…During the Quaternary period, the East China Sea (ECS) land bridge connected the forests of East China, South Japan, and probably the Korean Peninsula [ 15 ], at the last glacial maximum (LGM: c. 21,000 years before present [ 16 ]), when sea levels were c. 85–130 m below the present [ 17 ]. The ECS has acted as a corridor for the two-way migration of animals and plants, providing the possibility of secondary contact for disjunct populations or related species between China and Japan, e.g., [ 18 , 19 , 20 , 21 ]. The ECS land bridge was covered in a large part by temperate deciduous forest, but may have comprised local arid patches of nonforested vegetation (e.g., steppe, grasslands) [ 16 ].…”

Plastome phylogenomic insights into the Sino‐Japanese biogeography of Diabelia (Caprifoliaceae)

“…3). Similarly, Zhao et al (2019) also failed to recover species monophyly in plastid data in Diabelia. Each of the two species recovered as nonmonophyletic in our analyses is coherent morphologically.…”

“…wenzhouensis are truly distinct species, their similarity in reproductive morphology could be due to coevolution of pollinators or fruit dispersal mechanisms. Zhao et al (2019) suggest that D. serrata is composed of two phylogroups with unique sets of plastid haplotypes and distinct geographic distributions, one in Japan (central and south Japan) and the other in Zhejiang, China ( fig. 2 from Zhao et al, 2019).…”

“…Zhao et al (2019) suggest that D. serrata is composed of two phylogroups with unique sets of plastid haplotypes and distinct geographic distributions, one in Japan (central and south Japan) and the other in Zhejiang, China ( fig. 2 from Zhao et al, 2019). The presence of only two sepals has been considered as the most reliable morphological character to identify D. serrata (see Hara, 1983).…”

“…Diabelia Landrein (Caprifoliaceae) represents an excellent opportunity to test plant speciation and phylogeography in the SJFR. This genus of shrubs was recently segregated from Abelia based on inflorescences of paired flowers appearing at the end of short shoots, and its separation is supported by DNA sequence data (Landrein, 2010;Wang et al, 2015Wang et al, , 2020Zhao et al, 2019). Based on the number and length of sepals, Hara (1983) recognized three Diabelia species, with further distinctions made as varieties and forms based on hair types, nectary shape, fusion of nectaries and corolla, and corolla color.…”