Lowe Chris D, Day Adam, Kemp Stephen J, Montagnes David J S
School of Biological Sciences, University of Liverpool, BioSciences Building, Crown Street Liverpool, L69 7ZB, United Kingdom.
J Eukaryot Microbiol. 2005 May-Jun;52(3):250-7. doi: 10.1111/j.1550-7408.2005.00034.x.
Oxyrrhis marina, a widely distributed marine protist, is used to model heterotrophic flagellate responses in microbial food webs. Although clonal variability occurs in protists, assessments of intraspecific diversity are rare; such assessments are critical, particularly where species are used as models in ecological studies. To address the extent of intraspecific variation within O. marina, we assessed diversity among 11 strains using 5.8S rDNA and ITS sequences. The 5.8S rDNA and ITS regions revealed high divergence between strains: 63.1% between the most diverse. To compare O. marina diversity relative to other alveolates, 18S rDNA sequences for five strains were analysed with sequences from representatives of the major alveolate groups. 18S rDNA also revealed high divergence in O. marina. Additionally, consistent with phylogenies based on protein coding genes, maximum likelihood analysis indicated that O. marina was monophyletic and ancestral to the dinoflagellates. To assess ecophysiological differences, growth rates of seven O. marina strains were measured at 10 salinities (10-55 per thousand). Two salinity responses occurred: one group achieved highest growth rates at high salinities; the other grew best at low salinities. There was no clear correlation between molecular, ecophysiological, or geographical differences. However, salinity tolerance was associated with habitat type: intertidal strains grew best at high salinities; open-water strains grew best at low salinities. These data indicate the need to examine many strains of a species in both phylogenetic and ecological studies, especially where key-species are used to model ecological processes.
海洋尖鼻藻（Oxyrrhis marina）是一种广泛分布的海洋原生生物，被用于模拟微生物食物网中异养鞭毛虫的反应。尽管原生生物中存在克隆变异性，但种内多样性评估却很少见；这种评估至关重要，特别是在物种被用作生态研究模型的情况下。为了探究海洋尖鼻藻种内变异的程度，我们使用5.8S rDNA和ITS序列评估了11个菌株之间的多样性。5.8S rDNA和ITS区域显示出菌株之间的高度差异：差异最大的菌株之间为63.1%。为了比较海洋尖鼻藻相对于其他有孔虫类的多样性，我们将五个菌株的18S rDNA序列与主要有孔虫类群代表的序列进行了分析。18S rDNA也显示出海洋尖鼻藻的高度差异。此外，与基于蛋白质编码基因的系统发育一致，最大似然分析表明海洋尖鼻藻是单系的，并且是甲藻的祖先。为了评估生态生理差异，我们在10个盐度（千分之10 - 55）下测量了7个海洋尖鼻藻菌株的生长速率。出现了两种盐度反应：一组在高盐度下达到最高生长速率；另一组在低盐度下生长最佳。分子、生态生理或地理差异之间没有明显的相关性。然而，耐盐性与栖息地类型有关：潮间带菌株在高盐度下生长最佳；开阔水域菌株在低盐度下生长最佳。这些数据表明，在系统发育和生态研究中都需要检查一个物种的多个菌株，特别是在关键物种被用于模拟生态过程的情况下。
