Breeding system data for populations of T. perfoliata

Both intrinsic and extrinsic forces work together to shape connectivity and genetic variation in populations across the landscape. Here we explored how geography, breeding system traits, and environmental factors influence the population genetic patterns of Triodanis perfoliata, a widespread mix-mating annual plant in the contiguous US. By integrating population genomic data with spatial analyses and modeling the relationship between breeding system and genetic diversity, we illustrate the complex ways in which these forces shape genetic variation. Specifically, we used 4,705 single nucleotide polymorphisms to assess genetic diversity, structure, and evolutionary history among 18 populations. Populations with more obligately selfing flowers harbored less genetic diversity (π: R2 = 0.63, P = 0.01, n = 9 populations), and we found significant population structuring (FST = 0.48). Both geographic isolation and environmental factors played significant roles in predicting the observed genetic diversity: we found that corridors of suitable environment appear to facilitate gene flow between populations, and that environmental resistance is correlated with increased genetic distance between populations. Last, we integrated our genetic results with species distribution modeling to assess likely patterns of connectivity among our study populations. Our landscape and evolutionary genetic results suggest that T. perfoliata experienced a complex demographic and evolutionary history, particularly in the center of its distribution. As such, there is no singular mechanism driving this species’ evolution. Together, our analyses support the hypothesis that breeding system, geography, and environmental variables shape the patterns of diversity and connectivity of T. perfoliata in the US.

Methods
Following methods in Ansaldi et al., 2018, we quantified the breeding system (i.e., extent of cleistogamy) in a subset of populations included in our genetic analyses. Because these analyses aimed to estimate the total floral input of each flower type in a population (total CH and CL), we used only individuals with fully mature stems (flowering completed), and populations for which we had access to N>20 vouchered individuals. Breeding system data for the OCN population (Otter Creek North Carolina) were derived from Ansaldi et al. 2018. The total average production of each flower type in each population was estimated by collecting whole individual, fully mature plants (range = 20–50; 33 = mean individuals per population). For each population we assessed the average number of CH flowers, number of CL flowers, total flower number and the proportion of flowers that were CH out of the total flower number (pCH)

内外动力协同作用，共同塑造了景观尺度下各类种群的连接模式与遗传变异格局。本研究聚焦于美国本土48州广泛分布的混合交配型一年生植物——穿叶风铃草（Triodanis perfoliata），探讨了地理因素、交配系统性状与环境因子如何影响其种群遗传格局。我们整合种群基因组数据、空间分析方法，并构建交配系统与遗传多样性间的关系模型，阐明了上述动力塑造遗传变异的复杂路径。具体而言，我们利用4705个单核苷酸多态性（single nucleotide polymorphisms, SNPs），对18个种群的遗传多样性、种群结构与演化历史开展了评估。结果显示，专性自交占比更高的种群遗传多样性水平更低（π: R² = 0.63, P = 0.01, n = 9个种群），且我们检测到显著的种群遗传结构（FST = 0.48）。地理隔离与环境因子均对观测到的遗传多样性具有显著预测效应：研究发现适宜生境廊道可促进种群间的基因交流，而环境阻力与种群间遗传距离的增大呈显著正相关。最后，我们将遗传分析结果与物种分布模型相结合，评估了本研究涉及种群间的潜在连接格局。本研究的景观遗传学与演化遗传学结果表明，穿叶风铃草经历了复杂的种群动态与演化历史，尤其在其分布区的核心区域。由此可见，不存在单一机制驱动该物种的演化。综上，本研究的分析结果支持以下假说：交配系统、地理因素与环境变量共同塑造了美国本土48州穿叶风铃草的遗传多样性与种群连接格局。

研究方法
参照Ansaldi等人2018年的研究方法，我们对纳入遗传分析的部分种群的交配系统（即闭花授粉（cleistogamy）程度）进行了量化。由于本研究旨在估算种群内各类花型的总花量（总开放授粉花（chasmogamous flowers, CH）与闭花授粉花（cleistogamous flowers, CL）），我们仅选取茎秆完全成熟（已完成开花）的个体，且仅纳入可获取≥20份凭证标本的种群。OCN种群（北卡罗来纳州奥特克里克）的交配系统数据源自Ansaldi等人2018年的研究。通过采集完整的成熟个体植株（样本量范围为20~50株，每个种群平均采集33株），我们估算了每个种群中各类花型的平均总产量。针对每个种群，我们统计了开放授粉花平均数量、闭花授粉花平均数量、总花量，以及开放授粉花占总花量的比例（pCH）。