Integrative taxonomy of five astome ciliates (Ciliophora, Astomatia) isolated from earthworms in Central Europe

Abstract

Four earthworm species, the endogeic Octolasion tyrtaeum (Savigny, 1826), the anecic Lumbricus terrestris Linnaeus, 1758 as well as the epigeic Eisenia fetida (Savigny, 1826) and Dendrobaena veneta (Rosa, 1886), were examined for the presence of astome ciliates. Based on the integrative taxonomic approach, five ciliate species were recognized in their gastrointestinal tracts: Metaradiophrya lumbrici (Dujardin, 1841), M. varians (de Puytorac, 1954), Anoplophrya lumbrici (Schrank, 1803), A. vulgaris de Puytorac, 1954 and A. nodulata (Dujardin, 1841). Their distinctness was assessed using the multivariate morphometric approach and molecular phylogenetic analyses. Although the two species of Metaradiophrya Jankowski, 2007 on the one hand and the two former species of Anoplophrya Stein, 1860 on the other, were not distinctly separated by the multivariate morphometric analyses, they were clearly delimited by the 18S rRNA gene sequences. Species within each genus also differed by their hosts, M. lumbrici and A. lumbrici occurred only in anecic earthworms while M. varians and A. vulgaris occured exclusively in epigeic earthworms. Only a single species, A. nodulata, was detected in endogeic earthworms. It was morphologically distinct from and did not cluster with the two other species of Anoplophrya but was nested within the paraphyletic assemblage containing other astomes from endogeic earthworms. This indicates that the evolution of endosymbiotic ciliates from earthworms has very likely proceeded through a specialization to various ecological groups of their host organisms.

Delimitation of five astome ciliate species isolated from the digestive tube of three ecologically different groups of lumbricid earthworms, using the internal transcribed spacer region and the hypervariable D1/D2 region of the 28S rRNA gene

“…This applies also to the species-rich astome genera Anoplophrya Stein, 1860 and Metaradiophrya Jankowski, 2007 [12]. Both have a difficult taxonomic history due to the paucity of morphologically diagnostic features available for sound species identification as well as due to the lack of information on intraspecific variability and host spectrum [12,[19][20][21][22][23]. The best way to obtain more robust species identification is an integrative approach that combines morphological and molecular data with ecological features [24].…”

“…Symbiotic ciliates are often thought of as rather promiscuous to their hosts [6,7], albeit the ciliate-animal symbiotic associations are only seldomly analyzed with the aid of sophisticated molecular taxonomic/systematic methods [8][9][10]. A part of the "promiscuity problem" might have been caused by a lack of reliable data on the associations of ciliate species with their hosts [11,12]. These issues can now be independently tested with molecular phylogenetic tools.…”

“…Recent phylogenetic studies have suggested that some endosymbiotic ciliates cluster according to associations with higher taxa of their hosts. For instance, astome ciliates originating from terrestrial oligochaetes form a clade that is sister to the cluster of astomes from marine polychaetes [11][12][13][14]; clevelandellid ciliates, which live in the hindgut of panesthiine cockroaches, form a monophyletic group [4,15]; and trichostome ciliates exhibit a clustering specific for higher taxa of their vertebrate hosts and individual gastrointestinal compartments [10,[16][17][18].…”

“…However, subtle morphological differences and their tiny sizes hinder proper species identification for many ciliates and molecular data are often required to corroborate the identity of the species. This applies also to the species-rich astome genera Anoplophrya Stein, 1860 and Metaradiophrya Jankowski, 2007 [12]. Both have a difficult taxonomic history due to the paucity of morphologically diagnostic features available for sound species identification as well as due to the lack of information on intraspecific variability and host spectrum [12,[19][20][21][22][23].…”

“…The best way to obtain more robust species identification is an integrative approach that combines morphological and molecular data with ecological features [24]. We adopted this strategy in order to examine species boundaries in five endosymbiotic ciliate species that had been isolated from the gastrointestinal tract of lumbricid earthworms in Western Slovakia, Central Europe [12]. Our previous multivariate morphometric analyses revealed an overlap between two Metaradiophrya species on one hand and two Anoplophrya species on the other one.…”