Old divergences in a boreal bird supports long-term survival through the Ice Ages

Takema Saitoh,Urban Olsson,Isao Nishiumi,Per Alström,Yoshimitsu Shigeta,Dawn Williams,Keisuke Ueda

doi:10.1186/1471-2148-10-35

Abstract

BackgroundUnlike 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.ResultsIn 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.ConclusionsThe 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.

Highlights

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
The results suggest that the Eastern Palearctic may have been almost free of ice during the Pleistocene, population bottlenecks and subsequent expansions have occurred in that region because of forest dynamics
The three Arctic Warbler clades are estimated to have diverged in close succession during the latter part of the Pliocene to early part of the Pleistocene, and all of them experienced population bottlenecks during the Pleistocene, they survived and maintained their respective integrity

Summary

Introduction

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. [17], and various rodents [18,19,20,21,22,23], as well as birds including ducks [24], shorebirds[25,26], woodpeckers [27,28], and several species of passerines [26,29,30,31,32,33,34,35,36,37,38,39,40,41] Most of these studies have reported little or no divergence over large areas of the northern Palearctic, some divergent clades, mostly dated to the Pleistocene, have been found in some species. Some phylogeographical studies of birds have dealt with groups of closely related species with extensive north-south distributions from the taiga to temperate forests in central China and the Himalayas, and some of these have found relatively deep divergences between boreal and more southern taxa, which date back to the Pliocene or early Pleistocene [42,43,44]

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