Nielson M, Lohman K, Sullivan J
Department of Fish and Wildlife Resources, University of Idaho, Moscow 83844-1136, USA.
Evolution. 2001 Jan;55(1):147-60. doi: 10.1111/j.0014-3820.2001.tb01280.x.
Tailed frogs are distributed in high-gradient streams within the disjunct mesic forests of the Pacific Northwest and represent the basal lineage of the anurans. We sequenced 1,530 nucleotides of the mitochondrial cytochrome b and NADH dehydrogenase subunit two genes from 23 populations and used parsimony, maximum-likelihood, and nested-clade analyses to estimate relationships among populations and infer evolutionary processes. We found two divergent haplotype clades corresponding with inland Rocky Mountain populations and coastal populations and separated by up to 0.133 substitutions per site. Within the coastal assemblage, haplotypes formed clades by mountain range with 0.010-0.024 substitutions per site divergence among populations. Inland haplotypes exhibited minimal genetic structure, with the exception of 0.021 substitutions per site distance between populations from the East Fork of the South Fork of the Salmon River and all other inland haplotypes. The magnitude of divergence between inland and coastal populations, as well as the paleobotanical record, suggest isolation of these lineages occurred during the late Miocene to early Pliocene, probably in response to the rise of the Cascade Mountains. Genetic structure within coastal and inland populations is consistent with isolation in refugia during the late Pliocene and early Pleistocene. Closely related inland haplotypes reflect range expansion following glaciation. The depth of divergence between inland and coastal populations supports the persistence of mesic forests within the inland Pacific Northwest throughout the Pleistocene and is congruent with patterns found in several other mesic forest species. Based on mitochondrial divergence and previous allozyme and morphological data, we recommend recognition of inland populations as a distinct species, Ascaphus montanus.
尾蟾分布于太平洋西北部间断性湿润森林内的高梯度溪流中，代表了无尾两栖类的基部谱系。我们对来自23个种群的线粒体细胞色素b和烟酰胺腺嘌呤二核苷酸脱氢酶亚基2基因的1530个核苷酸进行了测序，并使用简约法、最大似然法和嵌套分支分析来估计种群间的关系并推断进化过程。我们发现了两个不同的单倍型分支，分别对应内陆落基山脉种群和沿海种群，每个位点的替换差异高达0.133。在沿海种群组合中，单倍型按山脉形成分支，但种群间每个位点的替换差异为0.010 - 0.024。内陆单倍型表现出最小的遗传结构，不过来自鲑鱼河南叉东支的种群与所有其他内陆单倍型之间每个位点的距离有0.021的替换差异。内陆和沿海种群之间的分化程度以及古植物学记录表明，这些谱系的隔离发生在中新世晚期至上新世早期，可能是对喀斯喀特山脉隆起的响应。沿海和内陆种群内的遗传结构与上新世晚期和更新世早期避难所中的隔离情况一致。密切相关的内陆单倍型反映了冰川作用后的范围扩张。内陆和沿海种群之间的分化深度支持了整个更新世期间太平洋西北部内陆湿润森林的持续存在，并且与其他几种湿润森林物种中发现的模式一致。基于线粒体分化以及先前的等位酶和形态学数据，我们建议将内陆种群识别为一个独特的物种，即蒙大拿尾蟾。
