Glacial survival or tabula rasa?: The history of North Atlantic biota revisited
Glacial survival or tabula rasa?: The history of North Atlantic biota revisited
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作者：
Brochmann, C;Gabrielsen, TM;Elven, R
直到 20 世纪 60 年代，人们几乎完全一致认为，如果没有冰期期间的原地生存，就无法解释北大西洋的分离和特有现象（“努纳塔克假说”）。另一种冰期后移民的“白板假说”被认为仅具有历史意义。在此，我们回顾了最近的地质、分子、分类和生物地理学数据，以重新审视这一观点。现在有强有力的地质证据表明北大西洋一些无冰区域位于晚威克塞尔/威斯康星冰盖的最大范围内，但尚未发现化石证明这些区域存在生命的连续原位存在。分子数据表明，许多植物和动物最近已经跨越大西洋迁徙，即使它们缺乏促进长距离扩散的机制。在其他物种中，存在深层的跨洋系统发育地理分裂，表明它们在两个或多个避难所中生存，但这些避难所可能位于冰盖之外。对于维管植物，我们提供了 77 种被视为北大西洋特有物种的北寒带植物、高山植物和北极类群的最新列表。特有程度很低（0.0-1.9%单区域特有现象）。四十种特有种出现在不止一处孤立的大西洋地区，这表明它们存在广泛的迁徙，并使对栖息地位置的推断变得复杂。三十四种特有物种可能不足以适应努纳塔克人的生存，可以用冰河后移民（或原位进化）来解释。在 43 种“耐寒”特有种中，没有一个异交二倍体可以表明长期进化。大多数耐寒的特有物种是无性或多倍体自花受精，其中一些是冰河后杂交起源的。其他的是冰期前的多倍体，它们在冰期后迁移或就地生存。一些无冰地区，例如广阔的格陵兰地区，可能支持了一些耐寒生物的生存。然而，自 20 世纪 60 年代以来积累的证据表明，北大西洋的特有现象和分离现象可以在不援引冰川原地生存的情况下得到解释。
Up to the 1960s, there was nearly complete consensus that disjunctions and endemism in the North Atlantic cannot be explained without in situ survival during the glaciations (the "nunatak hypothesis"). The alternative "tabula rasa hypothesis" of posiglacial immigration was regarded to be of merely historical interest. Herein we review recent geological, molecular, taxonomic, and biogeographic data to re-examine this view. There is now strong geological evidence for some ice-free North Atlantic areas within the maximum limits of the Late Weichselian/Wisconsian ice sheets, but no fossils have been found to prove continuous in situ existence of life in these areas. Molecular data suggest that many plants and animals have migrated recently across the Atlantic, even if they lack mechanisms promoting long-distance dispersal. In other species, there are deep trans-oceanic phylogeographic splits suggesting survival in two or more refugia, but these refugia may have been located outside the ice sheets. For vascular plants, we provide an updated list of 77 north boreal, alpine, and arctic taxa accepted as North Atlantic endemics. The degree of endemism is very low (0.0-1.9% single-region endemism). Forty endemics occur in more than one of the isolated Atlantic regions, indicating extensive migration and complicating inferences on the location of refugia. Thirty-four endemics are probably not hardy enough for nunatak survival and are explained by postglacial immigration (or in situ evolution). Among the 43 "hardy" endemics, there is not a single outcrossing diploid that could suggest long-term evolution. Most of the hardy endemics are asexual or self-fertilizing polyploids, some of postglacial hybrid origin. Others are preglacial polyploids which immigrated postglacially or survived in situ. Some ice-free areas, such as the extensive Greenlandic ones, may have supported survival of some hardy organisms. The evidence accumulated since the 1960s suggests, however, that endemism and disjunctions in the North Atlantic can be explained without invoking in situ glacial survival.