Department of Biology, and Centre for Comparative Genomics and Evolutionary Bioinformatics, Dalhousie University, Halifax, Canada; Department of Botany, University of British Columbia, Vancouver, Canada(1).
Institute of Parasitology, Biology Centre, Czech Academy of Sciences, České Budějovice, Czech Republic.
Mol Phylogenet Evol. 2021 Jun;159:107088. doi: 10.1016/j.ympev.2021.107088. Epub 2021 Feb 2.
Euglenids are a well-known group of single-celled eukaryotes, with phototrophic, osmotrophic and phagotrophic members. Phagotrophs represent most of the phylogenetic diversity of euglenids, and gave rise to the phototrophs and osmotrophs, but their evolutionary relationships are poorly understood. Symbiontids, in contrast, are anaerobes that are alternatively inferred to be derived euglenids, or a separate euglenozoan group. Most phylogenetic studies of euglenids have examined the SSU rDNA only, which is often highly divergent. Also, many phagotrophic euglenids (and symbiontids) are uncultured, restricting collection of other molecular data. We generated transcriptome data for 28 taxa, mostly using a single-cell approach, and conducted the first multigene phylogenetic analyses of euglenids to include phagotrophs and symbiontids. Euglenids are recovered as monophyletic, with symbiontids forming an independent branch within Euglenozoa. Spirocuta, the clade of flexible euglenids that contains both the phototrophs (Euglenophyceae) and osmotrophs (Aphagea), is robustly resolved, with the ploeotid Olkasia as its sister group, forming the new taxon Olkaspira. Ploeotids are paraphyletic, although Ploeotiidae (represented by Ploeotia spp.), Lentomonas, and Keelungia form a robust clade (new taxon Alistosa). Petalomonadida branches robustly as sister to other euglenids in outgroup-rooted analyses. Within Spirocuta, Euglenophyceae is a robust clade that includes Rapaza, and Anisonemia is a well-supported monophyletic group containing Anisonemidae (Anisonema and Dinema spp.), 'Heteronema II' (represented by H. vittatum), and a clade of Neometanema plus Aphagea. Among 'peranemid' phagotrophs, Chasmostoma branches with included Urceolus, and Peranema with the undescribed 'Jenningsia II', while other relationships are weakly supported and consequently the closest sister group to Euglenophyceae remains unresolved. Our results are inconsistent with recent inferences that Entosiphon is the evolutionarily pivotal sister either to other euglenids, or to Spirocuta. At least three transitions between posterior and anterior flagellar gliding occurred in euglenids, with the phylogenetic positions and directions of those transitions remaining ambiguous.
眼虫是一类广为人知的单细胞真核生物，包含有光合型、渗透营养型和吞噬营养型成员。吞噬营养型代表了眼虫的大部分系统发育多样性，它们起源于光合型和渗透营养型，但它们的进化关系还知之甚少。与此相反，共生体是厌氧生物，它们被推断要么是衍生的眼虫，要么是一个单独的眼虫动物群。大多数眼虫的系统发育研究仅检查了 SSURNA，而该序列通常高度分化。此外，许多吞噬营养型眼虫（和共生体）尚未被培养，这限制了其他分子数据的收集。我们生成了 28 个分类群的转录组数据，主要使用单细胞方法，并进行了首次包括吞噬营养型和共生体的眼虫多基因系统发育分析。眼虫被重建为单系群，共生体在眼虫动物群中形成一个独立的分支。旋鞭毛类是包含光合型（眼虫纲）和渗透营养型（Aphagea）的柔性眼虫类群，得到了稳健的解决，其姐妹群是 ploeotid 属的 Olkasia，形成了新的分类群 Olkaspira。pleo 类是并系的，尽管 Ploeotiidae（以 Ploeotia spp.为代表）、 Lentomonas 和 Keelungia 形成了一个稳健的分支（新的分类群 Alistosa）。Petalomonadida 在基于外群的分析中作为其他眼虫的姐妹支分支得非常稳健。在旋鞭毛类中，眼虫纲是一个稳健的类群，其中包含 Rapaza，而 Anisonemia 是一个支持良好的单系群，包含 Anisonemidae（Anisonema 和 Dinema spp.）、“ Heteronema II”（以 H. vittatum 为代表）和 Neometanema 加上 Aphagea 的一个分支。在“peranemid”吞噬营养型中，Chasmostoma 与包含的 Urceolus 分支，而 Peranema 与未描述的“Jenningsia II”分支，而其他关系支持较弱，因此 Euglenophyceae 的最接近姐妹群仍未解决。我们的结果与最近的推断不一致，即 Entosiphon 是其他眼虫或旋鞭毛类的进化关键姐妹群。眼虫至少发生了三次前后鞭毛滑行的转变，这些转变的系统发育位置和方向仍然不明确。
