Conjugation in the spirotrich ciliate Halteria grandinella (Müller, 1773) Dujardin, 1841 (Protozoa, Ciliophora) and its phylogenetic implications

Abstract

The conjugation of Halteria grandinella was studied in protargol preparations. The isogamontic conjugants fuse partially with their ventral sides to a homopolar pair. The first maturation division generates dramatic transformations: (i) the partners obtain an interlocking arrangement; (ii) the number of bristle kineties decreases from seven to four in each partner; and (iii) the right conjugant loses its buccal membranelles, the left the whole adoral zone. The remaining collar membranelles arrange around the pair's anterior end and are shared by both partners; finally, the couple resembles a vegetative specimen in size and outline. The vegetative macronucleus fragments before pycnosis. The micronucleus performs three maturation divisions, but only one derivative each performs the second and third division. The synkaryon divides twice, producing a micronucleus, a macronucleus anlage, and two disintegrating derivatives. Scattered somatic kinetids occur during conjugation, but disappear without reorganization. An incomplete oral primordium originates in both partners. The conjugation of Halteria grandinella resembles in several respects that of hypotrich spirotrichs; however, the majority of morphological, ontogenetical, and ultrastructural features still indicates an affiliation with the oligotrich and choreotrich spirotrichs. Accordingly, the cladistic analysis still contradicts the genealogy based on the sequences of the small subunit rRNA gene.

Reconciling Cladistic and Genetic Analyses in Choreotrichid Ciliates (Ciliophora, Spirotricha, Oligotrichea)

“…As Agatha and Strüder‐Kypke (), Foissner et al. (), and Agatha and Foissner () already discussed many of the characters analysed, only the new or newly coded features for choreotrichid ciliates are described here.…”

“…The characters and their states are summarized in Table 1, and their distribution among the taxa is shown in Table 2. As Agatha and Stru¨der-Kypke (2007), Foissner et al (2007), and Agatha and Foissner (2009) already discussed many of the characters analysed, only the new or newly coded features for choreotrichid ciliates are described here.…”

“…The consideration of the halteriids and oligotrichids in the present cladistic analysis of the choreotrichids allows not only the reconstruction of the last common ancestor, which entered the pelagial, but also the detection of convergences and adaptations to the planktonic life style. Besides the data already analysed by Agatha and Stru¨der-Kypke (2007), recent findings from live and silver-impregnated specimens and electron microscopic studies are included (Agatha 2008(Agatha , 2010a(Agatha , b, 2011Agatha and Foissner 2009;Agatha and Tsai 2008;Foissner et al 2007;Kim and Taniguchi 2007;Kim Y.-O. et al 2008Kim Y.-O.…”

“…Concerning the position of the halteriids, the genetic and morphologic data are inconsistent: the halteriids are located within the stichotrich outgroup and thus distinctly apart from the oligotrichids and choreotrichids in the molecular trees (Shin et al 2000;Snoeyenbos-West et al 2002;Weisse et al 2008), whereas the morphology and pattern of cell division indicate a sister-group relationship with a cluster formed by the oligotrichids and choreotrichids (Agatha 2004b;Agatha and Foissner 2009;Foissner et al 2007;Petz and Foissner 1992).…”

Phylogeny of the Order Tintinnida (Ciliophora, Spirotrichea) Inferred from Small‐ and Large‐Subunit rRNA Genes

“…The subclasses Stichotrichia, Oligotrichia, and Choreotrichia were found to be monophyletic, although this cannot be confirmed for Oligotrichia in the SSU + LSU rRNA analysis, as it was represented only by S. rassoulzadegani . The clustering of Halteria grandinella within the Stichotrichia is confirmed in the concatenated analysis, contrary to some cytological and morphogenetic features that suggest an affiliation with the Oligotrichia (Agatha and Foissner ). The monophyly of the order Tintinnida was poorly supported in the SSU rRNA‐based phylogeny (MLS = 65%; BPP ≤ 0.90).…”