Hainan Island in south China is a key part of the globally important Indo-Burma biodiversity hotspot, while the origin and maintenance of its species richness remains largely unexplored. In this study, we combined nuclear ITS and cpDNA trnL-trnF and ycf1b sequences to evaluate the genetic structure and phylogeographic patterns of the Hainan-endemic Primulina heterotricha (Gesneriaceae). The results showed significant phylogeographic patterns with low within-population genetic diversity and significant genetic differentiation among populations (Fst = 0.708 ± 0.319 and 0.826 ± 0.209 for nrDNA and cpDNA). Three clades were identified with little gene flow (Nm << 1 for nrDNA and cpDNA), which is supported by our STRUCTURE v.2.3.4 analyses. Our analyses detected two vicariance events at c. 0.83 and c. 0.48 Myr, and suggest that these three genetically-separated groups were isolated by two big rivers (Changhua River and Wanglou River), that likely acted as barriers to gene flow. The magnitude of isolation was positively correlated to the size of the rivers, with the greater barrier effect associated with the larger Changhua River. Our results highlight for the first time the critical role of riverine isolation in the patterns of intraspecific evolution of plant populations on Hainan Island.

Anthropogenic disturbances have long been acknowledged to be one of the primary threats to biodiversity worldwide, while little is still understood about how human-built infrastructure affects the gene flows and phylogeographic structure of plants. Such information is helpful for the conservation and restoration of human-disturbed ecosystems. Here we studied effects of a big river with a huge reservoir and two expressways on an island-endemic Primulina heterotricha (Gesneriaceae) on Hainan Island, China, one of the key parts of the glob ally important Indo-Burma biodiversity hotspot. By applying comparative phylogeography using one nuclear ribosomal DNA and two chloroplast DNA sequences, we estimated the levels of genetic diversity and differentiation in 176 and 117 individuals collected, respectively, before (in 2016) and after (in 2022) the construction of two expressways in Hainan Island, from the same eight populations of P. heterotricha. We found that Primulina heterotricha significantly increased nuclear genetic differentiation during the period 2016–2022, which coincides with the opening of the two expressways. Also notably, the sharing of ribotypes among the three groups of populations separated by the expressway network almost disappeared for the same period. Moreover, the changes in the significance of genetic barriers before and after road construction suggest that geographic isolation caused by both the reservoir and the expressways is key for understanding the present phylogeographical patterns of P. heterotricha. We provide direct evidence that anthropogenic infrastructures such as reservoirs and expressways have been capable of increasing genetic differentiation and, thus, modifying the phylogeographical pattern of P. heterotricha, in just a six-year period (or two generations of the study plant). To mitigate such negative pressure, we suggest establishing ecological corridors to enhance gene exchange between the two sides of the anthropogenic barriers.

Disjunct distribution is a key issue in biogeography and ecology, but it is often difficult to determine relative roles of dispersal vs. vicariance in disjunctions. Conandron ramondioides (Gesneriaceae) is a tertiary relict monotypic species distributed disjunctively in mainland China, Taiwan Island and Japan, where is a key region for understanding evolution and diversification of modern angiosperms. Population phylogenetic and phylogeographic structures of a comprehensive sampling of C. ramondioides by ddRAD sequencing were assessed, combined ABC modeling and SDM to infer the effects of multiple glaciation periods and to survey climatic niche differences by checking putative population divergence models and demographic scenarios. We found a very high degree of genetic differentiation among mainland China, Taiwan Island and Japan, with very limited gene flow between regions and a clear Isolation by Distance pattern. Mainland China and Japan clades diverged first from a widespread ancestral population in middle Miocene, followed by a later divergence between mainland China and Taiwan Island clades at early Pliocene. Three current groups have survived in various glacial refugia during LGM, and experienced contraction and/or bottlenecks since their divergence during Quaternary glacial cycles, with strong niche divergence between mainland China + Japan and Taiwan Island ranges. Overall, we verified a predominant role of vicariance in the current disjunction of monotypic genus Conandron. The sharp phylogenetic separation, ecological niche divergences among these three groups and the great number of private alleles in all populations sampled indicate a considerable time of independent evolution, and suggests the need of a taxonomic survey to detect potentially overlooked taxa.