Data_Sheet_1_Genetic Diversity and Conservation Status of Helianthus verticillatus, an Endangered Sunflower of the Southern United States.docx

Evaluating species diversity and patterns of population genetic variation is an essential aspect of conservation biology to determine appropriate management strategies and preserve the biodiversity of native plants. Habitat fragmentation and potential habitat loss are often an outcome of a reduction in naturally occurring wildfires and controlled prescribed burning, as seen in Helianthus verticillatus (whorled sunflower). This endangered, wild relative of the common sunflower, Helianthus annuus, is endemic to four locations in Alabama, Georgia, and Tennessee, United States. Despite its endangered status, there is no recovery plan for H. verticillatus, and knowledge related to its basic plant biology and importance in ecosystem services is mostly unknown. In this study, we utilized 14 microsatellite loci to investigate fine-scale population structure and genetic diversity of H. verticillatus individuals found on two sampling sites within the Georgia population. Our results indicated moderate genetic diversity and the presence of two distinct genetic clusters. Analyses of molecular variance indicated that the majority of variance was individually based, thus confirming high genetic differentiation and limited gene flow between H. verticillatus collection sites. The evidence of a population bottleneck in these sites suggests a recent reduction in population size that could be explained by habitat loss and population fragmentation. Also, high levels of linkage disequilibrium were detected, putatively suggesting clonal reproduction among these individuals. Our study provides a better understanding of fine-scale genetic diversity and spatial distribution of H. verticillatus populations in Georgia. Our results can underpin an original recovery plan for H. verticillatus that could be utilized for the conservation of this endangered species and to promote its persistence in the wild.

评估物种多样性与种群遗传变异模式，是保护生物学中制定合理管理策略、保护本土植物生物多样性的核心环节。如轮叶向日葵（Helianthus verticillatus）所面临的情况：自然野火与计划性受控火烧的减少，常会引发生境破碎化与潜在生境丧失。这种作为普通向日葵（Helianthus annuus）野生近缘种的濒危植物，仅分布于美国阿拉巴马州、佐治亚州和田纳西州的4处地点。尽管处于濒危状态，轮叶向日葵目前尚无任何恢复计划，学界对其基础植物生物学特性以及其在生态系统服务中的重要性的认知仍十分有限。本研究选取14个微卫星（microsatellite）位点，对佐治亚州种群内2个采样点的轮叶向日葵个体进行了精细种群结构与遗传多样性分析。研究结果显示，该种群具有中等水平的遗传多样性，且存在两个显著分化的遗传聚类群。分子方差分析结果表明，绝大多数遗传变异来源于个体间，证实了轮叶向日葵各采样点间存在高度遗传分化与有限的基因交流。各采样点存在种群瓶颈的证据表明，其种群规模近期出现缩减，这一现象可由生境丧失与种群破碎化得到解释。同时，研究检测到高水平的连锁不平衡（linkage disequilibrium），推测这些个体可能存在克隆繁殖。本研究增进了学界对佐治亚州轮叶向日葵种群精细遗传多样性与空间分布格局的认知。本研究结果可为轮叶向日葵制定首部恢复计划提供科学支撑，助力该濒危物种的保护及其野外种群的存续。