Department of Life Science, Rikkyo University, 3-34-1 Nishi-ikebukuro, Toshima-ku, Tokyo, Japan.
BMC Evol Biol. 2010 Feb 4;10:35. doi: 10.1186/1471-2148-10-35.
Unlike northern Europe and most of northern North America, the Eastern Palearctic and the northwesternmost tip of North America are believed to have been almost unglaciated during the Quarternary glacial periods. This could have facilitated long-term survival of many organisms in that area. To evaluate this, we studied the phylogeography in east Asia and Alaska of a boreal migratory passerine bird, the Arctic Warbler Phylloscopus borealis, and compared our results with published data on especially North American species.
In a sample of 113 individuals from 18 populations we identified 42 haplotypes of the mitochondrial cytochrome b gene, which separated into three clades: A--Alaska and mainland Eurasia (except Kamchatka); B--Kamchatka, Sakhalin and Hokkaido; and C--Honshu, Shikoku and Kyushu (i.e. Japan except Hokkaido). The oldest split among these clades, between A/B and C, is estimated to have taken place sometime between the mid Pliocene and early Pleistocene, and the second divergence, between clades A and B, in the early to mid Pleistocene. Within all of the three main clades, there are signs of population expansion.
The Arctic Warbler separated into three main clades in close succession around the Pliocene/Pleistocene border, with the two northern clades diverging last. All three clades probably experienced population bottlenecks during the Pleistocene as a result of range shifts and contractions, but nevertheless survived and maintained their integrities. Several other clades of Northeastern Palearctic birds are noted to have diversified during the Pliocene. In contrast, avian species or phylogroups presently occupying formerly glaciated North American ground are generally younger. The differences between these regions could be due to slower speciation rates in the Eastern Palearctic due to less fragmentation of forest habitats during glacial periods, or to longer survival of Eastern Palearctic clades as a result of less severe conditions in that region compared to northern North America. Several other Palearctic organisms show concordant biogeographical patterns to that of the Arctic Warbler, indicating common causes of their diversifications.
与北欧和北美大部分地区不同，人们认为第四纪冰期期间，东亚东部和北美最西北端几乎没有冰川。这可能促进了该地区许多生物的长期生存。为了评估这一点，我们研究了东亚和阿拉斯加的一种北方迁徙雀形目鸟类北极莺 Phylloscopus borealis 的系统地理学，并将我们的结果与北美物种的已发表数据进行了比较。
在来自 18 个种群的 113 个个体的样本中，我们鉴定出线粒体细胞色素 b 基因的 42 个单倍型，这些单倍型分为三个分支：A--阿拉斯加和欧亚大陆大陆（堪察加半岛除外）；B--堪察加半岛、萨哈林岛和北海道；C--本州、四国和九州（即北海道以外的日本）。这些分支之间最古老的分裂，A/B 和 C 之间，估计发生在中新世中期到更新世早期之间，而第二次分裂，A 和 B 分支之间，发生在更新世早期到中期。在所有三个主要分支中，都有种群扩张的迹象。
北极莺在中新世/更新世边界附近以紧密的顺序分为三个主要分支，最北部的两个分支最后分化。在更新世期间，由于范围的转移和收缩，所有三个分支都可能经历了种群瓶颈，但它们仍然存活并保持完整。其他几个东北古北界鸟类的分支在中新世也发生了多样化。相比之下，目前占据以前冰川覆盖的北美的鸟类物种或系统发育群通常较年轻。这些地区之间的差异可能是由于东亚东部的物种形成率较慢，因为在冰期期间森林栖息地的破碎化较少，或者由于与北美北部相比，该地区的条件不太恶劣，导致东亚东部的分支存活时间更长。其他一些古北界生物表现出与北极莺一致的生物地理模式，表明它们多样化的共同原因。
