Carstens Bryan C, Stevenson Angela L, Degenhardt Jeremiah D, Sullivan Jack
Department of Biological Sciences, Moscow, Idaho 83844-3051, USA.
Syst Biol. 2004 Oct;53(5):781-92. doi: 10.1080/10635150490522296.
Mesic forests in the North American Pacific Northwest occur in two disjunct areas: along the coastal and Cascade ranges of Oregon, Washington, and British Columbia as well as the Northern Rocky Mountains of Idaho, Montana, and British Columbia. Over 150 species or species complexes have disjunct populations in each area, and a priori hypotheses based on phytogeography and geology potentially explain the disjunction via either dispersal or vicariance. Here, we test these hypotheses in the disjunct salamander complex Plethodon vandykei and P. idahoensisby collecting genetic data (669 bp of Cyt b) from 262 individuals. Maximum likelihood analysis indicated reciprocal monophyly of these species, supporting the ancient vicariance hypothesis, whereas parametric bootstrap and Bayesian hypothesis testing allow rejection of the dispersal hypothesis. The coalescent estimate of the time since population divergence (estimated using MDIV) is 3.75 x 106 years, and the 95%credibility interval of this value overlaps with the geological estimate of vicariance, but not the hypothesized dispersal. These results are congruent with the pattern seen in other mesic forest amphibian lineages and suggest disjunction in amphibians may be a concerted response to a geological/climatological event. WithinP. idahoensis, we tested the corollary hypothesis of an inland Pleistocene refugium in the Clearwater drainage with nested clade analysis and coalescent estimates of population growth rate (g). Both analyses support post-Pleistocene expansion from the Clearwater refugium. We corroborated this result by calculating Tajima's Dand mismatch distribution within each drainage, showing strong evidence for recent population expansion within most drainages. This work demonstrates the utility of statistical phylogeography and contributes two novel analytical tools: tests of stationarity with respect to topology in the Bayesian estimation, and the use of coalescent simulations to test the significance of the population growth-rate parameter.
沿着俄勒冈州、华盛顿州和不列颠哥伦比亚省的海岸山脉及喀斯喀特山脉，以及爱达荷州、蒙大拿州和不列颠哥伦比亚省的北落基山脉。超过150个物种或物种复合体在每个区域都有不连续的种群，基于植物地理学和地质学的先验假设可能通过扩散或隔离分化来解释这种不连续性。在这里，我们通过收集262个个体的遗传数据（细胞色素b的669 bp），对不连续的蝾螈复合体范氏东美螈和爱达荷东美螈进行了这些假设的检验。最大似然分析表明这些物种互为单系，支持了古老的隔离分化假设，而参数自展法和贝叶斯假设检验则可以排除扩散假设。种群分化时间的溯祖估计（使用MDIV估计）为3.75×10⁶年，该值的95%可信区间与隔离分化的地质估计值重叠，但与假设的扩散时间不重叠。这些结果与在其他中生林两栖动物谱系中看到的模式一致，并表明两栖动物的不连续性可能是对地质/气候事件的协同响应。在爱达荷东美螈中，我们用嵌套进化枝分析和种群增长率（g）的溯祖估计，检验了清水河流域内陆更新世避难所的推论假设。两种分析都支持了更新世后从清水避难所的扩张。我们通过计算每个流域内的 Tajima's D 和错配分布证实了这一结果，显示出大多数流域内近期种群扩张的有力证据。这项工作证明了统计系统地理学的实用性，并贡献了两种新的分析工具：贝叶斯估计中关于拓扑结构的平稳性检验，以及使用溯祖模拟来检验种群增长率参数的显著性。
