Plants growing in similar climates with extensively overlapping distributions may exhibit similar phylogeographic patterns, due to similarities in range shifts during past climatic oscillations. We tested and exploited this expectation in a comparison of the evolutionary and demographic histories of two related and co-distributed species endemic to Japan—Rhododendron pentaphyllum and R. quinquefolium. Genetic variation in sequences of noncoding chloroplast DNA regions and hundreds of nuclear single nucleotide polymorphisms were used to investigate 191 individuals from 13 populations of R. pentaphyllum and 142 individuals from 10 populations of R. quinquefolium. We found that the two species were not each other’s closest relative, and we found different times to the most recent common ancestor of extant populations based on both chloroplast DNA and nuclear SNPs. Rhododendron pentaphyllum exhibited higher genetic variation between populations than R. quinquefolium, while the two species had similar patterns of genetic divergence between regions with slightly different divergence times. These lines of evidence suggest that the similar ranges of the two species are the result of repeated range shifts since speciation during climatic oscillations.

由于过去气候振荡过程中距离变化的相似性，在相似气候下生长且分布范围广泛重叠的植物可能会表现出相似的系统地理模式。在比较两个日本特有的相关和共同分布物种-杜鹃花和西洋参的进化和人口历史时，我们测试并利用了这种期望。利用非编码叶绿体DNA区域序列的遗传变异和数百个核单核苷酸多态性研究了13个R种群的191个个体。五叶金枪鱼和来自10个种群的西洋参叶片的142个个体。我们发现这两个物种不是彼此最接近的亲戚，并且基于叶绿体DNA和核SNPs，我们发现了与现存种群的最新共同祖先不同的时间。五花杜鹃在种群之间的遗传变异高于西洋参，而两个物种在区域之间的遗传分歧模式相似，但发散时间略有不同。这些证据表明，由于气候振荡期间的物种形成，这两个物种的相似范围是重复范围变化的结果。