Alonso-García Marta, Villarreal A Juan Carlos, McFarland Kenneth, Goffinet Bernard
Département de Biologie, Université Laval, Quebec City, QC, Canada.
Smithsonian Tropical Research Institute, Ancón, Panama.
Front Plant Sci. 2020 May 8;11:495. doi: 10.3389/fpls.2020.00495. eCollection 2020.
The southern Appalachian (SA) is one of the most biodiversity-rich areas in North America and has been considered a refugium for many disjunct plant species, from the last glacial period to the present. Our study focuses on the SA clonal hornwort, J. C. Villarreal & K. D. McFarland. This hornwort was described from North Carolina and is widespread in the SA, growing on rocks near or submerged in streams in six and one watersheds of the Tennessee (TR) and Alabama (AR) Rivers, respectively. Males and female populations occur in different watersheds, except in the Little Tennessee (TN) River where an isolated male population exists ca. 48 km upstream from the female populations. The sex ratio of 1:0 seems extreme in each population. In this study, we use nuclear and organellar microsatellites from 250 individuals from six watersheds (seven populations) in the SA region and two populations from Mexico (23 individuals). We, then, selected 86 individuals from seven populations and used genotyping by sequencing to sample over 600 bi-allelic markers. Our results suggest that the SA and Mexican plants are a nested within a clade of sexual tropical populations. In the US populations, we confirm an extreme sex ratio and only contiguous US watersheds share genotypes. The phylogenetic analysis of SNP data resolves four clusters: Mexican populations, male plants (Little Pigeon and Pigeon river watersheds) and two clusters of female plants; one from the Little Tennessee and Hiwassee Rivers (TR) and the other from the Ocoee (TR) and Coosa (AR) Rivers. All clusters are highly differentiated (Fst values over 0.9). In addition, our individual assignment analyses and PCAs reflect the phylogenetic results grouping the SA samples in three clades and recovering males and female plants with high genetic differentiation (Fst values between 0.5 and 0.9 using microsatellites and bi-allelic markers). Our results point to Pleistocene events shaping the biogeographical pattern seen in US populations. The extreme sex ratio reflects isolation and highlights the high vulnerability of the populations in the SA.
阿巴拉契亚山脉南部（SA）是北美生物多样性最丰富的地区之一，从末次冰期至今，一直被视为许多间断分布植物物种的避难所。我们的研究聚焦于SA地区的克隆金鱼藻，即J. C. 比利亚雷亚尔和K. D. 麦克法兰所描述的那种金鱼藻。这种金鱼藻最初是在北卡罗来纳州被描述的，在SA地区广泛分布，分别生长在田纳西河（TR）和阿拉巴马河（AR）流域的六个和一个流域中靠近溪流或淹没在溪流中的岩石上。除了在小田纳西河（TN），雄性和雌性种群分布在不同的流域，在小田纳西河中，有一个孤立的雄性种群存在于距离雌性种群上游约48公里处。每个种群中1:0的性别比例似乎都很极端。在这项研究中，我们使用了来自SA地区六个流域（七个种群）的250个个体以及来自墨西哥的两个种群（23个个体）的核微卫星和细胞器微卫星。然后，我们从七个种群中挑选了86个个体，并使用测序基因分型来对600多个双等位基因标记进行采样。我们的结果表明，SA地区和墨西哥的植物嵌套在一个有性热带种群的进化枝中。在美国的种群中，我们证实了极端的性别比例，并且只有相邻的美国流域共享基因型。对单核苷酸多态性（SNP）数据的系统发育分析解析出四个聚类：墨西哥种群、雄性植株（小鸽子河和鸽子河流域）以及两个雌性植株聚类；一个来自小田纳西河和希瓦西河流域（TR），另一个来自奥科伊河（TR）和库萨河（AR）流域。所有聚类都高度分化（Fst值超过0.9）。此外，我们的个体分配分析和主成分分析（PCA）反映了系统发育结果，即将SA样本分为三个进化枝，并发现雄性和雌性植株具有高度的遗传分化（使用微卫星和双等位基因标记时，Fst值在0.5到0.9之间）。我们的结果表明更新世事件塑造了美国种群中所见的生物地理模式。极端的性别比例反映了隔离，并突出了SA地区种群的高度脆弱性。
