Abstract
Subfamily Cyrtandroideae (Gesneriaceae) comprises a broadly distributed group of rocky-slope herbs, with China being the center of its distributional range. The normal growth of many species within the family is particularly dependent on special habitats. Due to the paucity of molecular studies, very little is known regarding East Asian herb phylogeographic pattern. Here, we investigate the molecular phylogeography of Boea clarkeana Hemsl., a unique resurrection herb endemic to China, focusing on geographically restrictive effects of habitat distribution on evolutionary history. Variation in three chloroplast DNA (cpDNA) intergenic spacers (psbA-trnH, rps12-rpl20, and trnL-trnF), the ribosomal internal transcribed spacer (ITS) and simple sequence repeats in expressed sequence tags (EST-SSRs) was investigated across 18 populations to assess genetic diversity, genetic structure and historical dynamics. Genetic diversity was low within populations (cpDNA, hS = 0.03, πS×103 = 0.17; ITS, hS = 0.16, πS×103 = 0.43) but high for species (cpDNA, hT = 0.82, πT×103 = 3.12; ITS, hT = 0.88, πT×103 = 6.39); 76 alleles were detected in this highly inbred species (FIS = 0.22), with a significantly low average of 1.34 alleles per locus. No cpDNA or ITS haplotypes were shared between regions. Based on cpDNA results, the Mt. Huangshan-Tianmu and Mt. Qinling-Daba haplotypes are ancestral; these two regions represent potential refugia. Although no evidence of significant retreat-migration phenomena during glacial cycles was detected, interglacial range expansion from northern Mt. Qinling-Daba was identified (121,457 yr BP). Rapid agricultural growth caused bottlenecks in many populations, especially on Mt. Huang-Tianmu. Habitat restriction and fragmentation, weak seed and pollen dispersal abilities, and long-term isolation caused by human-induced or environmental changes are considered the main causes of extinction of several populations and low genetic diversity within populations and regions. These analyses clarify the effects of habitat restriction on B. clarkeana, representing an evolutionary reference for similar gesneriads, and enrich our understanding of the molecular phylogeography of East Asian rocky-slope herbs.
Highlights
A stable climate, mature plant communities in vast landscapes, high spatial heterogeneity and a long evolutionary history have laid the foundation for floristic richness in China
Genetic structure was further revealed by analysis of molecular variance (AMOVA); most of the variation existed among groups (95.89%, FST = 0.994), and significant phylogeographic structure was found (NST = 0.995 > GST = 0.964, both P < 0.05)
Nan) were distant from the other chlorotypes, especially C6, which exhibited more than 22 mutational steps differing from the other chlorotypes, indicating that it had been isolated from the other chlorotypes and had evolved into a distinct type over time
Summary
A stable climate, mature plant communities in vast landscapes, high spatial heterogeneity and a long evolutionary history have laid the foundation for floristic richness in China. This area is an important region of diversity in the Northern Hemisphere (with a very high level of endemism [1]) and an important center for species conservation, speciation and evolution [2]. Gesneriaceae is a family of aesthetically appealing herbs with high ornamental value, among which the center of the distributional range of subfamily Cyrtandroideae occurs in China [18]. There have been few studies involving DNA sequences [26,27,28], and no research is available regarding the molecular phylogeography of these plants, even though such information may aid in understanding genetic structures and geographical distribution patterns in relation to the intrazonal distribution of Gesneriaceae
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