Ciliophora, Spirotricha, Oligotrichida) Based on Somatic Ciliary Patterns and Ontogenetic Data Sabine Agatha∗

European Journal of Protistology 47 (2011) 51–56

Updated hypothesis on the evolution of oligotrichid ciliates (Ciliophora, Spirotricha, Oligotrichida) based on somatic ciliary patterns and ontogenetic data Sabine Agatha∗

University of Salzburg, Department of Organismic Biology, Hellbrunnerstrasse 34, A-5020 Salzburg, Austria

Received 23 January 2010; received in revised form 24 August 2010; accepted 6 September 2010

Abstract

The two recently established genera Apostrombidium Xu et al., 2009 and Varistrombidium Xu et al., 2009 and the analysis of ontogenetic data in Strombidium constrictum, S. montagnesi, S. wilberti, Omegastrombidium elegans, and Paratontonia gracillima necessitated a revision of the hypothesis about the somatic ciliary pattern evolution in oligotrichid ciliates. As a consequence, the species-rich genus Strombidium was split, establishing two genera for species with a horizontal girdle kinety posterior to the oral primordium: Opisthostrombidium nov. gen. with the extrusome attachment sites along the anterior margin of the girdle kinety and posterior to the oral primordium and Foissneridium nov. gen. with the extrusome attachment sites distinctly apart from the girdle kinety and anterior to the oral primordium. The ontogenetic data revealed that the -shaped girdle kinety pattern evolved convergently from the Pseudotontonia pattern with its horizontal girdle kinety in the tailed genus Paratontonia and from the Novistrombidium pattern with its dextrally spiralled girdle kinety in the tailless genus Omegastrombidium. The somatic ciliary pattern of the latter genus probably gave rise to the patterns of Apostrombidium and Varistrombidium. © 2010 Elsevier GmbH. All rights reserved.

Keywords: Ciliophora; New genera; Oligotrichida; Somatic ciliary pattern; Taxonomy

Introduction of somatic ciliary patterns suggested by Agatha (2004a),by including the genera and the ontogenetic data on Strombidium Although the somatic ciliature of the Oligotrichida (Cil- constrictum, S. montagnesi, S. wilberti, Omegastrombid- iophora, Spirotricha) typically comprises only a girdle and ium elegans, and Paratontonia gracillima. Thus, this study a ventral kinety, the diversity of ciliary patterns created by provides a better understanding of the diversity within the these two rows is considerable. Recently, Xu et al. (2009) Oligotrichida. published descriptions of two strombidiid genera with unique somatic ciliary patterns: Varistrombidium possessing ﬁve somatic kineties and Apostrombidium having two inverted U- shaped kinety fragments in the right and left cell halves. The Material and Methods present paper assigns positions for these two genera within the Strombidiidae and expands on the hypothesized evolution The original literature was used (references in Agatha 2004a; Agatha 2004c; Agatha et al. 2005; Liu et al. 2009; Skovgaard and Legrand 2005; Song 2005; Wilbert and Song ∗Fax: +43 662 8044 5698. 2005; Xu and Song 2006; Xu et al. 2005, 2006a,b,c, 2007, E-mail address: [email protected]. 2008, 2009) and the following genera were considered:

Apostrombidium Xu, Warren and Song, 2009; Cyrtostrom- Agatha (2004a) assumed a single origin of the -shaped bidium Lynn and Gilron, 1993; Laboea Lohmann, 1908; girdle kinety pattern derived from the Type II pattern. How- Limnostrombidium Krainer, 1995; Novistrombidium Song ever, ontogenetic data indicate that this only occurred in the and Bradbury, 1998; Omegastrombidium Agatha, 2004; Par- Type IV pattern of Omegastrombidium (Fig. 1), while the - allelostrombidium Agatha, 2004; Paratontonia Jankowski, shaped pattern of Paratontonia (Type VI pattern) probably 1978; Pelagostrombidium Krainer, 1991; Pseudotontonia evolved from the Type V pattern by the posterior migration Agatha, 2004; Spirostrombidium Jankowski, 1978; Spiroton- of both girdle kinety ends, as indicated by the position of tonia Agatha, 2004; Strombidium Claparède and Lachmann, the oral primordium posterior to the girdle kinety (Fig. 1). 1859; Tontonia Fauré-Fremiet, 1914; and Varistrombidium Accordingly, the -shaped girdle kinety pattern developed Xu, Warren and Song, 2009. Note, a description and diagno- not only convergently in the tailed (tontoniid) and tailless sis of Varistrombidium were given by Xu, Warren, and Song (strombidiid) taxa, as suggested by Agatha (2004b), but also (2009), referring to an original description by Xu, Yi, Song from different patterns. and others in press, but this latter publication does not exist; The Type X pattern of Apostrombidium and the Type XII hence, Xu, Warren, and Song (2009) were considered the pattern of Varistrombidium probably developed from such a authorities on this genus. -shaped girdle kinety pattern. It is more parsimonious to By regarding the somatic kineties in the Oligotrichida assume that these tailless genera originated from the Type IV as homologs of the dorsal kineties in the hypotrich and pattern of the tailless genus Omegastrombidium than from the stichotrich spirotrichs (Agatha 2004a,b; Agatha and Strüder- Type VI pattern of the tailed genus Paratontonia; however, Kypke 2007; Foissner et al. 2007), the evolution of the ciliary ontogenetic and/or molecular data are required to support this patterns can be inferred from the orientation of the somatic conjecture for Apostrombidium. While the Type X pattern of dikinetids (based on which basal body bears the cilium) Apostrombidium probably evolved from the Type IV pattern and the location of the oral primordium. The orientation by a dorsal split of the girdle kinety and an extension of the of the somatic dikinetids was inferred from a line drawing new kinety ends to the posterior cell pole, the development of of the ventral side in Apostrombidium and a micrograph of the Type XII pattern in Varistrombidium was more complex. the posterior ventral cell portion in Varistrombidium; both First, a hypothetical intermediate Type XI pattern was gen- patterns were verified by D. Xu (Department of Biology, erated by an elongation and sinistral torsion of the parallel North Carolina Central University, NC, USA) and W. Song girdle kinety ends, while the ventral kinety disappeared. Next, (Laboratory of Protozoology, Ocean University of China, the dorsal portion of the first whorl broke, and the new kinety Qingdao, China), using the type slides of A. pseudokielum ends extended to the posterior cell pole, cutting through the and the protargol slides of V. kielum. kinety spirals and producing the several ciliary row fragments Data on the ontogenesis of Strombidium montagnesi and characteristic of the Type XII pattern. A similar, but conver- S. wilberti were published by Xu et al. (2006c) and Song gent dorsal split of the girdle kinety occurred not only in the (2005), respectively. The position of the oral primordium Type X pattern of Apostrombidium, but also in the Type VIII was studied in S. constrictum, using protargol slides from pattern of Cyrtostrombidium. the type locality kindly provided by D.H. Lynn (Depart- Besides the Type VI pattern of Paratontonia (see above) ment of Integrative Biology, University of Guelph, Canada), and the Type VII pattern of Laboea and Spirotontonia,two and in Paratontonia gracillima, using protargol-impregnated further somatic ciliary patterns probably developed from the specimens from the North Pacific kindly provided by the Type V pattern: the Type VIII pattern of Cyrtostrombidium Tohoku University Museum (Sendai, Japan). In Omegastrom- (the pre-equatorial position of the girdle kinety suggests this bidium elegans, however, the position of the oral primordium origin) and the Type IX pattern of Strombidium constrictum, could only be inferred from micrographs, because of the two S. montagnesi, and S. wilberti. In contrast to the Type V pat- slides stated to be deposited in the Natural History Museum in tern, e.g., found in the type species Strombidium sulcatum London, one was inadequate to evaluate the target structures (Fauré-Fremiet 1912, 1953), the formation of the oral pri- and the other was not included into the collection. Hence, the mordium commences anteriorly to the girdle kinety in the information was taken from Figures 41 and 42 in Song et al. latter pattern (refer to Fig. 1; own data; Song 2005; Xu et al. (2000; p. 340). 2006c). Since the extrusome attachment sites usually form a stripe along the anterior margin of the girdle kinety in the olig- otrichids, the insertion of the extrusomes distinctly separate Results and Discussion from the girdle kinety and anterior to the oral primordium in S. constrictum (Fig. 7) suggests the former position and Evolution of the Somatic Ciliary Patterns course of the girdle kinety. Thus, it seems likely that the Type IX pattern evolved from the Type V pattern by a migration In Agatha (2004a), the hypothetical evolution of the of the horizontal girdle kinety below the oral primordium, oligotrichid somatic ciliature comprised six patterns: the as proposed by Agatha (2004b). However, this arrangement Types I–V, and VII. Below, five further patterns are recog- of the girdle kinety developed twice independently: in S. nized, viz., the Types VI, VIII–X, and XII (Fig. 1). montagnesi and S. wilberti, both the girdle kinety and the S. Agatha / European Journal of Protistology 47 (2011) 51–56 53

Fig. 1. Hypothetical evolution of oligotrichid somatic ciliary patterns. Small arrows mark the orientation of the kineties (from posterior to anterior). The dikinetidal somatic kineties of the ancestor (Type 0) were reduced to two and became dextrally spiralled, producing the Type I pattern. Next, the ventral kinety orientated longitudinally in the Type II pattern. The Type III pattern evolved by an elongation of the posterior girdle kinety end, which orientated inversely along the ventral kinety. The Type IV pattern developed by the posterior migration of the right girdle kinety portion, while in the Type V pattern, the left portion migrated anteriorly above the oral primordium. The Type VI pattern was generated by the posterior migration of both girdle kinety ends. In the Type VII pattern, the right girdle kinety end elongated and spiralled sinistrally. The horizontal girdle kinety split dorsally (arrowhead), producing the Type VIII pattern, while the Type IX pattern developed by the posterior migration of the horizontal girdle kinety below the oral primordium. The Type X pattern was generated by a dorsal split (arrowhead) of the girdle kinety and an elongation of the new kinety ends to the posterior pole. The evolution of the Type XII pattern commenced with an elongation and sinistral torsion of both kinety ends, producing the hypothetical Type XI pattern. Next, the ﬁrst kinety whorl split dorsally (arrowhead), and the new ends elongated to the rear end, breaking through the kinety spirals and producing several kinety fragments.0–Type 0 of the ancestor, I–XII – Types I–XII, GK – girdle kinety, OP – oral primordium, VK – ventral kinety. associated extrusome attachment sites migrated posteriorly, within the stripe of extrusome attachment sites (Foissner et while in S. constrictum, merely the girdle kinety migrated al. 1999). posteriorly. Accordingly, two new strombidiid genera must be established based on the differences in the position of the girdle kinety and the extrusome attachment sites (see ‘Taxo- Comparison with Molecular Phylogenies nomic Implications’). Probably, the pelagostrombidiid genus Limnostrombidium also belongs to the Type IX pattern, as the The hypothetical evolution of the oligotrichid somatic cil- neoformation organelle opens anteriorly to the girdle kinety iary patterns suggested above is tested by a comparison with 54 S. Agatha / European Journal of Protistology 47 (2011) 51–56

the maximum parsimony and neighbor-joining analyses (Gao et al. 2009a,b; Kim et al. 2010); thus, many polytomies were not resolved. Accordingly, the following comparison cannot be detailed. Within the monophyletic Oligotrichida, the genus Novistrombidium branches early, followed by the genus Parallelostrombidium and a cluster of Spirostrombidium species. Since the Parallelostrombidium species (GenBank FJ422988) sequenced by Gao et al. (2009a) was described as Novistrombidium orientale by Liu et al. (2009), the gene tree corroborates the present hypothesis, in which the Type II pattern of Novistrombidium gives rise to the Type III pattern of Spirostrombidium (Fig. 1). The paraphyly of the genus Strombidium in the SSrRNA gene trees might be due to the unresolved polytomies and/or undersampling. On the other hand, it cannot be excluded that future studies will reveal morphological features of the cell and/or the resting cyst, justifying further splits of the species- rich genus Strombidium. In the gene trees, the genus Pseudotontonia represents an adelphotaxon to a cluster formed by the genera Laboea and Spirotontonia, supporting the close relationship of the Type V and VII patterns (Fig. 1). In contrast to the proposal by Agatha (2004b), the sinistrally spiralled course of the girdle kinety (Type VII pattern) apparently did not evolve convergently in the tontoniids and strombidiids, but was apparently present in the tailed common ancestor of the genus Spirotontonia and the probably secondarily tailless genus Laboea (Gao et al. 2009a). Besides the somatic ciliary pattern, the absence of a tail, and the position of the oral primordium, the close relationship of the genera Omegastrombidium (Type IV pattern) and Varistrombidium (Type XII pattern) is indicated by the molecular data. In general, the evolution of the oligotrichid somatic ciliary patterns suggested above thus matches the recent gene trees.

Taxonomic Implications

The ontogenetic data provided by Song (2005) and Xu et al. (2006c) and those gathered by me necessitate the estab- Figs. 2–7. Ventral views of oligotrichid dividers (2, after Song et lishment of two new genera. al. 2000; 3, 7, originals; 4, 5, after Xu et al. 2006c; 6, after Song 2005; protargol impregnation; 2, 4, 5, combination of line draw- ings and micrographs). 2. Omegastrombidium elegans,43␮m long. Genus Opisthostrombidium nov. gen. 3. Paratontonia gracillima,37␮m long. 4–6. Opisthostrombidium montagnesi nov. comb. (4, 5) and O. wilberti nov. comb. (6),? ␮m. Diagnosis 7. Foissneridium constrictum nov. comb., 53 ␮m long. EX – extrusome attachment sites, GK – girdle kinety, OP – oral primordium, Strombidiidae with the oral primordium anterior to the hor- VK – ventral kinety. izontal girdle kinety and the associated extrusome attachment sites. Ventral kinety longitudinal. phylogenies inferred from the small subunit ribosomal RNA (SSrRNA) gene sequences. In the recently published SSr- Type Species RNA gene trees of the Oligotrichida, most basal nodes were not well supported, having bootstrap values less than 50% in Strombidium montagnesi Xu, Song and Warren, 2006. S. Agatha / European Journal of Protistology 47 (2011) 51–56 55

Etymology ever, the horizontal stripe of extrusome attachment sites is pre-equatorial in S. constrictum and thus not only distinctly Composite of the Greek preﬁx opistho (behind) and the separate from the subterminally located horizontal girdle genus-group name Strombidium, referring to the position of kinety, but also anterior to the oral primordium. These dif- the girdle kinety and the extrusome attachment sites posterior ferences in the position of the extrusome attachment sites to the oral primordium. Neuter gender. and the oral primordium relative to the girdle kinety justify a generic separation of the species from Strombidium and Comparison with Similar Genera and Species Opisthostrombidium. Since Jankowski (2007) subsequently designated Conocylis helix Meunier, 1910 as type of the Assignable genus Conocylis Meunier, 1910, which might also include C. striata Meunier, 1910, a new genus, viz., Foissneridium In Strombidium montagnesi and S. wilberti, the formation nov. gen., is established for S. constrictum, which becomes of the oral primordium commences anteriorly to the hori- Foissneridium constrictum (Meunier, 1910) nov. comb. zontal girdle kinety and its associated extrusome attachment sites (refers to Fig. 1). The species are thus separated on generic level from Strombidium (the oral primordium forms posteriorly to the horizontal girdle kinety in the type and fur- Acknowledgements ther species; Agatha 2003; Agatha et al. 2005; Fauré-Fremiet 1912, 1953; Kormos and Kormos 1958; Petz 1994; Song This study was supported by the Austrian Science Foun- and Wang 1996), becoming Opisthostrombidium montagnesi dation (FWF, Project P20461-B17). Many thanks are due to (Xu, Song and Warren, 2006) nov. comb. and Opisthostrom- Dapeng Xu (Department of Biology, North Carolina Central bidium wilberti (Song, 2005) nov. comb. University, North Carolina, USA) and Weibo Song (Labora- tory of Protozoology, Ocean University of China, Qingdao, China) for their help to ascertain the orientation of the somatic Genus Foissneridium nov. gen. dikinetids in the genera Apostrombidium and Varistrom- bidium. Thanks are also due to Denis Lynn (Department Diagnosis of Integrative Biology, University of Guelph, Canada) and the Tohoku University Museum (Sendai, Japan) for provid- Strombidiidae with the oral primordium posterior to the ing protargol slides. Furthermore, I wish to thank David horizontal stripe of extrusome attachment sites and anterior Montagnes for his helpful comments and some linguistic to the horizontal girdle kinety. Ventral kinety longitudinal. improvements.

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