Department of Biology, University of Florida, Gainesville, FL 32611, USA; Florida Museum of Natural History, University of Florida, Gainesville, FL 32611, USA.
Department of Biology, University of Florida, Gainesville, FL 32611, USA.
Mol Phylogenet Evol. 2018 Jun;123:88-100. doi: 10.1016/j.ympev.2018.02.016. Epub 2018 Feb 26.
Disjunct distributions have intrigued biologists for centuries. Investigating these biogeographic patterns provides insight into speciation and biodiversity at multiple spatial and phylogenetic scales. Some disjunctions have been intensively studied, yet others have been largely overlooked and remain poorly understood. Among the lesser-known disjunction patterns is that between the mountain ranges of western North America. Flora and fauna endemic to the mountains of this region provide important systems for investigating causes and results of disjunctions, given the relatively recent geological formation of this area and the intense climatic fluctuations that have occurred since its formation. In Micranthes (Saxifragaceae), which has high rates of montane endemism, two species, M. bryophora and M. tolmiei, show this biogeographical pattern. By reconstructing a time-calibrated phylogeny based on 518 low-copy nuclear markers and including multiple populations of each species from the Coast Ranges, Cascades, Sierra Nevada, and Rocky Mountains, this study provides a biogeographical and temporal framework for the evolution of Micranthes in western North America. Strongly supported east-west differentiated clades are recovered for M. bryophora and M. tolmiei in both maximum likelihood and coalescent-based species tree reconstructions. Biogeographic analysis suggests different patterns of dispersal for both taxa and the dating analyses recovered contrasting ages for each clade. Due to both the different geographic patterns and the timing of the initial diversification of each taxon corresponding to different geologic and climatic events, the disjunction patterns shown for these taxa are suggested to be an example of biogeographical pseudocongruence.
间断分布模式令生物学家们着迷了数个世纪。研究这些生物地理分布模式可以深入了解物种形成和生物多样性在多个空间和系统发育尺度上的情况。一些间断分布模式已经得到了深入研究，而其他模式则在很大程度上被忽视，仍然知之甚少。在不太为人知的间断分布模式中，有一个是在北美洲西部的山脉之间。该地区山脉特有的动植物为研究间断的原因和结果提供了重要的系统，因为该地区的地质形成相对较近，而且自形成以来经历了强烈的气候变化。在Micranthes（虎耳草科）中，有两个物种，M. bryophora 和 M. tolmiei，表现出这种生物地理分布模式，该物种具有高山特有种的高比率。通过基于 518 个低拷贝核标记重建一个时间校准的系统发育树，并包括来自海岸山脉、喀斯喀特山脉、内华达山脉和落基山脉的每个物种的多个种群，本研究为北美西部 Micranthes 的进化提供了一个生物地理和时间框架。在最大似然和基于合并的物种树重建中，都强烈支持 M. bryophora 和 M. tolmiei 的东西分化支系。生物地理分析表明，这两个分类群的扩散模式不同，而且每个支系的约会分析恢复了不同的年龄。由于每个分类群的地理模式和初始多样化的时间对应于不同的地质和气候事件，因此这些分类群的间断分布模式被认为是生物地理假同构的一个例子。
