PREMISE Recent phylogeographic work suggests the existence of latitudinal gradients in genetic diversity in northern Mexican plants, but very few studies have examined plants of the Chihuahuan Desert. Tidestromia lanuginosa is a morphologically variable annual species whose distribution includes the Chihuahuan Desert Region. Here we undertook phylogeographic analyses of chloroplast loci in this species to test whether genetic diversity and differentiation of Mexican populations of T. lanuginosa change along a latitudinal gradient and whether diversity is higher in Coahuila, consistent with ideas of lower plant community turnover during the Pleistocene. METHODS Haplotype network, maximum likelihood tree, and Bayesian phylogenetic haplotype were reconstructed, and genetic diversity was assessed among 26 populations. Barrier analysis was used to explore barriers to gene flow. RESULTS Four major population groups were identified, corresponding with physiographic provinces in Mexico. Each population group displayed high levels of genetic structure, haplotype, and nucleotide diversity. Diversity was highest in southern populations across the species as a whole and among the Chihuahuan Desert populations. CONCLUSIONS Tidestromia lanuginosa provides an important example of high phylogeographic and genetic diversity in plants of northern Mexico. Barriers to gene flow among the major population groups have most likely been due to a combination of orographic, climatic, and edaphic variables. The high genetic diversity of T. lanuginosa in southern and central Coahuila is consistent with the hypothesis of full-glacial refugia for arid-adapted plants in this area, and highlights the importance of this region as a center of diversity for the Chihuahuan Desert flora.

中文翻译：

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Tidestromia lanuginosa 的高系统地理学和遗传多样性支持墨西哥科阿韦拉州南部和中部干旱适应植物的全冰川避难

前提 最近的系统地理学工作表明，墨西哥北部植物的遗传多样性存在纬度梯度，但很少有研究检查过奇瓦瓦沙漠的植物。Tidestromia lanuginosa 是一种形态可变的一年生物种，其分布包括奇瓦瓦沙漠地区。在这里，我们对该物种的叶绿体基因座进行了系统地理学分析，以测试墨西哥 T. lanuginosa 种群的遗传多样性和分化是否沿纬度梯度变化，以及科阿韦拉的多样性是否更高，这与更新世期间植物群落周转率较低的想法一致。方法重建单倍型网络、最大似然树和贝叶斯系统发育单倍型，评估26个种群的遗传多样性。障碍分析用于探索基因流动的障碍。结果 确定了四个主要人口群体，与墨西哥的自然地理省份相对应。每个群体都表现出高水平的遗传结构、单倍型和核苷酸多样性。在整个物种和奇瓦瓦沙漠种群中，南部种群的多样性最高。结论 Tidestromia lanuginosa 提供了墨西哥北部植物高度系统地理学和遗传多样性的重要例子。主要人群之间基因流动的障碍很可能是由于地形、气候和土壤变量的组合。科阿韦拉南部和中部 T. lanuginosa 的高遗传多样性与该地区干旱适应植物的全冰期避难假说一致，