Data from: Rethinking refugia: tree topology, divergence dates, and demographic history trace the distribution of the endangered Plymouth gentian (Sabatia kennedyana) from the Pleistocene glaciation to present day

Premise of study: Molecular population genetics is a powerful tool to infer how species responded to past environmental change. In the northern hemisphere, interest is increasing in how species responded to changes in ice coverage and temperature during the last glaciation maximum (LGM, between 18000–21000 yr ago) with a common assumption that glacial refugia were located at the southern edge of a species range. Methods: We reconstructed the glacial and postglacial phylogeography of Sabatia kennedyana, a member of the Atlantic Coastal Plains Flora with a current distribution from Nova Scotia (NS) to South Carolina, using both cpDNA and nuclear markers. We also examined clinal variation in morphological traits, in particular relative investment in asexual vs sexual growth. Key results: We find strong evidence that the species did not reside in southern glacial refugia, but rather in primary glacial refugia off the exposed continental shelf extending from Cape Cod and that this area was responsible for the founding of modern populations across the range from Nova Scotia (NS) to the United States. Additionally, based on the finding of higher cpDNA diversity and older cpDNA lineages in NS, we propose that multiple founder events occurred in NS, while only a single lineage gave rise to current populations in the United States. Conclusions: By understanding how S. kennedyana responded to past shifts in climate and by identifying areas of high genetic diversity in the northern range edge, we discuss the potential response of the species to future climate change scenarios.

研究背景：分子群体遗传学是推断物种如何响应过往环境变化的有力工具。在北半球，学界对物种在末次冰盛期（LGM，距今18000至21000年）如何响应冰盖与温度变化的研究兴趣日益高涨，学界普遍认为冰期避难所位于物种分布范围的南部边缘。
研究方法：本研究以叶绿体DNA（cpDNA）与核标记为分析手段，重建了大西洋海岸平原植物类群成员Sabatia kennedyana的冰期及冰后系统地理学历史；该物种当前的分布范围从新斯科舍省（NS）延伸至南卡罗来纳州。同时，我们还分析了其形态性状的梯度变异，尤其是无性生长与有性生长的相对资源投入。
研究结果：我们发现充分证据表明，该物种并未栖息于南部冰期避难所，而是存活于从科德角延伸出的裸露大陆架外缘的原生冰期避难所中；正是这一区域促成了从新斯科舍省（NS）至美国境内所有现代种群的奠基。此外，基于新斯科舍省地区较高的cpDNA多样性与更古老的cpDNA谱系这一发现，我们提出该物种在新斯科舍省存在多次奠基事件，而美国境内的现存种群仅由单一谱系演化而来。
研究结论：通过阐明S. kennedyana如何响应过往气候变迁，并识别出分布范围北缘的高遗传多样性区域，我们探讨了该物种对未来气候变化情景的潜在响应。