Laboratory of Protistology and Aquatic Ecology, Ghent University, Krijgslaan 281 - S8, 9000 Gent, Belgium.
Protist. 2013 Jan;164(1):101-15. doi: 10.1016/j.protis.2012.04.001. Epub 2012 May 2.
Recent morphology-based studies indicate that freshwater diatom floras in the Antarctic comprise a significant share of endemics among a majority of apparently cosmopolitan species. Given the widespread (pseudo)cryptic species diversity in diatoms, we assessed the molecular divergence and temperature-dependent growth characteristics between Antarctic and non-Antarctic strains for two presumed species with a cosmopolitan distribution, namely Pinnularia borealis and Hantzschia amphioxys. Molecular phylogenies based on the plastid gene rbcL and the nuclear 28S rDNA (D1-D3 region) revealed that both taxa consist of multiple lineages, each including a distinct Antarctic lineage. A molecular clock estimates the origin of P. borealis at 35.8 (30-47) million years (Ma) ago, making this the oldest known diatom species complex. The Antarctic P. borealis lineage is estimated to have diverged 7.8 (2-15) Ma ago, after the geographical and thermal isolation of the Antarctic continent. Despite not being psychrophilic, the Antarctic lineages of P. borealis and H. amphioxys have a lower optimal growth temperature and upper lethal temperature than most lineages from more temperate regions, indicating niche differentiation. Together, this suggests that many presumed cosmopolitan Antarctic diatom species are in fact species complexes, possibly containing Antarctic endemics with low temperature preferences.
最近基于形态的研究表明，南极淡水硅藻区系在大多数明显的世界性物种中包含了大量的特有种。鉴于硅藻中广泛存在（拟）隐种多样性，我们评估了两种假定具有世界性分布的物种，即北极海链藻和弯角藻的南极和非南极菌株之间的分子分歧和温度依赖性生长特征。基于质体基因 rbcL 和核 28S rDNA（D1-D3 区）的分子系统发育表明，这两个分类群都由多个谱系组成，每个谱系都包括一个独特的南极谱系。分子钟估计北极海链藻的起源是在 3580 万年前（30-47Ma），这使其成为已知最古老的硅藻物种复合体。南极北极海链藻谱系估计在 780 万年前（2-15Ma）发生分歧，此时南极大陆在地理和热隔离之后。尽管不是嗜冷的，但北极海链藻和弯角藻的南极谱系的最佳生长温度和最高致死温度都低于大多数来自温带地区的谱系，这表明存在生态位分化。总的来说，这表明许多假定的世界性南极硅藻物种实际上是物种复合体，可能包含对低温有偏好的南极特有种。
