The effect of the geographic isolation on genetic variations and population structure of Euphrasia nankotaizanensis, an endemic and threatened alpine herb in Taiwan
The reduction of current distribution and genetic diversity, and affecting genetic structure of alpine herbs are as consequence of climate change, together with geographic isolation and small population size. Euphrasia nankotaizanensis (Scrophulariaceae), is a rare alpine herb that is endemic to Taiwan. Only four remaining populations were distributed in Xue Mountain, Nanhu Mountain, and Cilai Mountain of Taiwan with small population sizes. In this study, we examined the level of genetic variability and reconstructed population genetic structure in this endangered species. As anticipated, we found lower levels of genetic diversity than other alpine plants, and little to no genetic variations within populations, which could be mainly attributed to small population size and random genetic drift. The nrDNA phylogeny uncovered a pattern with reciprocal monophyly of four populations. The lack of monophyly of four population at cpDNA likely resulted from lineage sorting or occasional long-distance seed dispersal. The phylogeographic analysis suggested the Nanhu Mountain probably is a refugium over the glacial maxima, agreeing the potential refugia in central Taiwan. Higher levels of genetic differentiation between populations were deduced from nrDNA than cpDNA. STRUCTURE and AMOVA analyses revealed that significant genetic differentiation between mountains in nrDNA was existed, also indicating a low gene exchange (or high genetic differentiation). The scenario resulted from the geographical isolation between mountains. Estimates of effective population sizes (Ne) and demography reflected lower Ne value and a recent population decline, probably implying the greater extinction risks for E. nankotaizanensis. The present molecular study found genetic depletion, and the considerable genetic differentiation among mountains, and should be considered in future conservation efforts for this species. In addition, the knowledge of current study can provide important insights into long-term potential of alpine herbs in Taiwan, which are useful for better prediction of their probable responses to future climate change.