Table1_Strong Genetic Structure Observed in Primulina danxiaensis, a Small Herb Endemic to Mount Danxia With Extremely Small Populations.DOCX

Danxia landform occurring sporadically in southern China is a unique type of petrographic geomorphology. It has nurtured about 400 rare or threatened plant and animal species, whose diversity, endemism, and conservation have called increasing scientific and public attentions. Among them, Primulina danxiaensis (W. B. Liao, S. S. Lin, and R. J. Shen) W. B. Liao and K. F. Chung is a tiny perennial grass species recorded only in Mount Danxia, a natural World Heritage Site as part of China’s Danxia. In this study, restriction site-associated DNA sequencing (RAD-seq) was performed to investigate genetic diversity among these 12 populations of P. danxiaensis. A total of 432,041 variant sites were detected in 84,779 loci across 94 samples. The expected heterozygosity (HE) ranged from 0.017 to 0.139. Bottleneck signals were detected in most populations, Tajima’s D tests showed that most loci could be under recent positive selection, and one of the six positively selected loci identified by BayeScan was annotated as tRNAGlu, which may contribute to the species’ adaptation to shady environment. STRUCTURE analysis and phylogenetic tree showed that the 12 populations of P. danxiaensis could be divided into four gene pools (clades) corresponding to their geographic locations, and significant correlation was observed between genetic and geographic distances. Our study demonstrated that P. danxiaensis maintained a middle level of genetic diversity and strong population structure; geographic distance could be an important factor limiting gene flow among populations of P. danxiaensis, which were only sporadically recorded in Mount Danxia.

零散分布于中国南方的丹霞地貌（Danxia landform）是一类独特的岩石地貌类型。该地貌孕育了约400种珍稀濒危动植物物种，其物种多样性、特有性及保护工作正日益受到科学界与公众的关注。其中，仅分布于作为中国丹霞世界自然遗产组成部分的丹霞山的小型多年生草本植物丹霞报春苣苔（Primulina danxiaensis (W. B. Liao, S. S. Lin & R. J. Shen) W. B. Liao & K. F. Chung）便是其一。本研究采用限制性位点关联DNA测序（restriction site-associated DNA sequencing, RAD-seq）技术，对丹霞报春苣苔的12个种群的遗传多样性展开分析。本次研究共在94份样本的84779个基因座中检测到432041个变异位点，预期杂合度（expected heterozygosity, HE）范围为0.017至0.139。多数种群均检测到瓶颈效应信号；塔伊马D检验（Tajima’s D tests）结果显示，多数基因座可能正处于近期正向选择作用下；通过BayeScan软件筛选出的6个受正向选择的基因座中，有1个被注释为谷氨酸转运RNA（tRNAGlu），该基因或有助于该物种适应荫蔽环境。群体结构分析（STRUCTURE）与系统发育树结果显示，丹霞报春苣苔的12个种群可依据地理分布划分为4个基因库（支系），且种群间遗传距离与地理距离呈现显著相关关系。本研究结果表明，丹霞报春苣苔的遗传多样性处于中等水平，且种群结构显著；仅零散分布于丹霞山的该物种，其种群间基因交流受限的重要影响因素之一或为地理距离。