Reconsideration of the Phylogenetic Positions of Five Peritrich Genera, Vorticella, Pseudovorticella, Zoothamnopsis, Zoothamnium, and Epicarchesium (Ciliophora, Peritrichia, Sessilida), Based on Small Subunit rRNA Gene Sequences

Abstract

In order to re-evaluate the systematics of sessilid peritrich ciliates, small subunit (SSU) rRNA gene sequences were determined for 12 species belonging to five genera: Vorticella, Pseudovorticella, Epicarchesium, Zoothamnium, and Zoothamnopsis. Phylogenetic trees were deduced using Bayesian inference, maximum parsimony, and maximum likelihood methods. The phylogenetic analyses suggest that (1) sessilids which have stalks with continuous myonemes that contract in a zig-zag fashion form a separate clade from those which have stalks that contract independently and in a spiral fashion, supporting the separation of the family Zoothamniidae from the family Vorticellidae and (2) Epicarchesium and Pseudovorticella, both of which have reticulate silverline systems, are more closely related to each other than to other vorticellids, suggesting that differences in the silverline system (i.e. transverse vs. reticulate) may be the result of genuine evolutionary divergence among sessilid peritrichs. However, the newly sequenced Zoothamnopsis sinica, which has a reticulate silverline pattern, nests within the unresolved Zoothamnium species that have transverse silverline patterns. Thus, there were at least two evolutions of the reticulate silverline pattern character state from a plesiomorphic transverse state in the peritrichid ciliates. The molecular work demonstrates the genus Zoothamnium to be paraphyletic in relation to morphological studies, and suggests that Astylozoon, Opisthonecta, and Vorticella microstoma possibly share a SSU rRNA secondary structure in the helix E10-1 region.

Phylogenomics solves a long-standing evolutionary puzzle in the ciliate world: The subclass Peritrichia is monophyletic

“…Further analyses including more members of Peniculia will likely resolve the position of this taxon. Another very frequent relationship is that of the Hymenostomatia as sister taxon to the Sessilida (Li et al, 2008;Sun et al, 2011;Utz et al, 2010;Zhan et al, 2009). In contrast, our analyses show that Hymenostomatia is sister to Scuticociliatia, confirming the phylogenomic analyses of Feng et al (2015).…”

“…Even so, the monophyly of the Peritrichia could not be rejected when employing statistical tests (Utz and Eizirik, 2007). In all of the above analyses the sessilids consistently grouped as sister to the hymenostomes, while the mobilids grouped with the peniculines (Li et al, 2008;Miao et al, 2001Miao et al, , 2004Zhan et al, 2009). Thus, Zhan et al (2009) proposed that the mobilids be separated from the sessilids and established as the new subclass Mobilia.…”

“…Sequences of the 18S rRNA have confirmed the monophyly of each of the two orders. However, the monophyly of the subclass has been rigorously debated: numerous molecular studies throughout the years have failed to recover monophyly (Gong et al, 2006;Li et al, 2008;Miao et al, 2001Miao et al, , 2004Sun et al, 2011;Williams and Clamp, 2007;Utz and Eizirik, 2007;Zhan et al, 2009). Zhan et al (2012) critically evaluated various methods of alignment and removal of ambiguous positions.…”

“…At the time, it was suggested that the taxon sampling might be inadequate. Even with increased taxon sampling, investigations have failed to unite the two lineages (Gong et al, 2006(Gong et al, , 2010Li et al, 2008;Utz and Eizirik, 2007;Utz et al, 2010). Even so, the monophyly of the Peritrichia could not be rejected when employing statistical tests (Utz and Eizirik, 2007).…”

Temporal structure of the peritrich ciliate assemblage in a large Neotropical lake

“…Peritrich ciliates (subclass Peritrichia) are very common organisms found in the periphytic communities, being also one of the most diversified group in the phylum Ciliophora, with more than 50 genera and 1,000 species described so far (Li et al 2008;Lynn 2008). With easy sampling, recognition, and possible standardization for temporal and spatial comparisons, peritrich ciliates have been widely used to evaluate and monitor responses to contamination in ecological and ecotoxicological investigations (Gong et al 2005;Xu et al 2009).…”