Santoferrara Luciana F, Tian Michael, Alder Viviana A, McManus George B
Department of Marine Sciences, University of Connecticut, 1080 Shennecossett Rd., Groton 06340, Connecticut, USA.
Department of Marine Sciences, University of Connecticut, 1080 Shennecossett Rd., Groton 06340, Connecticut, USA.
Protist. 2015 Feb;166(1):78-92. doi: 10.1016/j.protis.2014.11.005. Epub 2014 Dec 8.
This study focuses on the utility of molecular markers for the discrimination of closely related species in tintinnid ciliates. We analyzed the ecologically important genus Helicostomella by sequencing part of the large-subunit rDNA (LSU rDNA) and the 5.8S rDNA combined with the internally transcribed spacer regions 1 and 2 (5.8S rDNA-ITS) from forty-five individuals collected in NW and SW Atlantic waters and after culturing. Although all described Helicostomella species represent a continuum of morphologies, forms with shorter or longer loricae would correspond to different species according to previous molecular data. Here we observed that long forms show both crypticity (i.e. two almost identical long forms with different DNA sequences) and polymorphism (i.e. some long forms develop significantly shorter loricae after culturing). Reviewing all available tintinnid sequences, we found that 1) three Helicostomella clusters are consistent with different species from a molecular perspective, although these clusters are neither clearly differentiated by their loricae nor unambiguously linked to described species, 2) Helicostomella is closely related (probably to the family or genus level) to four "Tintinnopsis-like" morphospecies, and 3) if considered separately, neither LSU rDNA nor 5.8S rDNA-ITS completely discriminate closely related species, thus supporting the use of multi-gene barcodes for tintinnids.
本研究聚焦于分子标记在辨别钟形虫类纤毛虫近缘物种方面的效用。我们通过对从北大西洋西北部和西南部水域采集并经培养的45个个体的大亚基核糖体DNA（LSU rDNA）部分、5.8S rDNA以及与内部转录间隔区1和2（5.8S rDNA - ITS）进行测序，分析了具有重要生态意义的螺旋口虫属。尽管所有已描述的螺旋口虫物种呈现出形态上的连续变化，但根据先前的分子数据，具有较短或较长外壳的形态应对应不同的物种。在此我们观察到，长形态既表现出隐匿性（即两种DNA序列不同但形态几乎相同的长形态）又表现出多态性（即一些长形态在培养后发育出明显更短的外壳）。回顾所有可用的钟形虫序列，我们发现：1）从分子角度来看，三个螺旋口虫类群与不同物种一致，尽管这些类群在外壳上既没有明显区分，也没有明确与已描述的物种相关联；2）螺旋口虫与四个“似铃壳虫属”形态种密切相关（可能在科或属的水平上）；3）如果单独考虑，LSU rDNA和5.8S rDNA - ITS都不能完全区分近缘物种，因此支持对钟形虫使用多基因条形码。
