Departamento de Biología Evolutiva, Instituto de Ecología, A.C. (INECOL), Carretera antigua a Coatepec, El Haya, Xalapa, Veracruz, Mexico.
Instituto de Investigaciones Forestales, Universidad Veracruzana, Xalapa, Veracruz, Mexico.
J Hered. 2019 Mar 5;110(2):229-246. doi: 10.1093/jhered/esy065.
The host dependence of mistletoes suggests that they track the distributions of their hosts. However, the factors that determine the geographic distribution of mistletoes are not well understood. In this study, the phylogeography of Psittacanthus sonorae was reconstructed by sequencing one nuclear (ITS) and two plastid (trnL-F and atpB-rbcL) regions of 148 plants from populations separated by the Sea of Cortez. Divergence time and gene flow were estimated to gain insight into the historical demography and geographic structuring of genetic variation. We also described and mapped the spatial distribution of suitable habitat occupied by P. sonorae and its most common host Bursera microphylla in the Sonoran Desert, along with their responses to Quaternary climate fluctuations using environmental data and ecological niche modeling (ENM). We detected environmental and genetic differentiation between the peninsular and continental P. sonorae populations. Population divergence occurred during the Pleistocene, around the time of the Last Glacial Maximum. No signals of population growth were detected, with net gene flow moving from the continent to the peninsula. ENM models indicate decoupled responses by the mistletoe and its main host to past climate changes. For the Last Interglacial to the present, most models produce only partial areas of overlap on both the peninsula and the continent. Our results support a scenario of Late-Pleistocene isolation and divergence with asymmetrical gene flow between peninsular and continental P. sonorae populations. Continental populations migrated to the peninsula and the spatial isolation probably produced genetic differentiation under different environmental conditions.
槲寄生的宿主依赖性表明它们跟踪其宿主的分布。然而，决定槲寄生地理分布的因素尚未得到很好的理解。在这项研究中，通过对来自科尔特斯海分隔的种群的 148 株植物的一个核（ITS）和两个质体（trnL-F 和 atpB-rbcL）区域进行测序，重建了 Psittacanthus sonorae 的系统地理学。估计了分歧时间和基因流，以深入了解遗传变异的历史人口统计学和地理结构。我们还描述并绘制了 P. sonorae 及其最常见的宿主 Bursera microphylla 在索诺兰沙漠中占据的适宜栖息地的空间分布，以及它们对第四纪气候波动的反应，使用环境数据和生态位建模 (ENM)。我们检测到半岛和大陆 P. sonorae 种群之间的环境和遗传分化。种群分歧发生在更新世，大约在末次冰盛期。没有检测到种群增长的信号，净基因流从大陆向半岛移动。ENM 模型表明，槲寄生及其主要宿主对过去气候变化的反应不同。对于末次间冰期到现在，大多数模型仅在半岛和大陆上产生部分重叠区域。我们的研究结果支持了晚更新世隔离和分歧的情景，半岛和大陆 P. sonorae 种群之间存在不对称的基因流。大陆种群迁移到半岛，空间隔离可能在不同的环境条件下产生遗传分化。
