Molecular Phylogeny of the Family Ophryscolecidae (Ciliophora, Litostomatea) Inferred from 18S rDNA Sequences

Morphometric and Molecular Analysis of Five-Spine Epidinium Morphotypes Taken from the Rumen of European Bison, Bison bonasus

An important feature of ruminal ciliates is their phenotypic plasticity, which makes their identification difficult. The common manifestation of the phenotypic plasticity in rumen ciliates is a change in their cell size and caudal spination. We analyzed various morphotypes of Epidinium with five caudal processes (spines) taken from the rumen of European bison (Bison bonasus). In the study, the cluster analysis and K-means analysis of morphometric data could not distinguish very similar morphotypes of Epidinium with five caudal processes. However, the morphotype of E. parvicaudatum prevailed (70%). The DNA of four individual E. parvicaudatum was isolated successfully from formaldehyde-preserved samples. The partial 18S rDNA gene sequences (about 350-400 bp) were identical to Epidinium sequences in GenBank (E. caudatum, a one-spine morphotype, and E. cattanei, a five-spine morphotype). It can be assumed that these short sequences cannot distinguish the differences between the Epidinium morphospecies. Complete gene sequences from various hosts and various molecular markers are necessary to reveal the validity of the Epidinium five-spine species. In conclusion, classical morphology should be supplemented with molecular data when more morphotypes of the rumen ciliate species are present in samples.

Insights into the systematics of the family Ophryoscolecidae (Ciliophora, Entodiniomorphida)

The family Ophryoscolecidae currently comprises 225 species of trichostomatid ciliates, subdivided in three subfamilies (Entodiniinae, Diplodiniinae, and Ophryoscolecinae). The last taxonomic review of the family was performed 55 years ago, but recent morphological and molecular studies indicate the need of a profound review on the systematics of this taxon, since its current taxonomy is insufficient to organize the diversity of the group. Here, we briefly review the systematics of the family Ophryoscolecidae based on information recovered from the literature and new morphological and molecular data. We add four new 18S rDNA sequences of ophryoscolecids to molecular databases, which contributed to improve the comprehension about intrafamily relationships within this group. Finally, we discuss some systematic problems and suggest approaches to resolve such inconsistencies in the future.

Trichostomatid Ciliates (Alveolata, Ciliophora, Trichostomatia) Systematics and Diversity: Past, Present, and Future

The gastrointestinal tracts of most herbivorous mammals are colonized by symbiotic ciliates of the subclass Trichostomatia, which form a well-supported monophyletic group, currently composed by ∼1,000 species, 129 genera, and 21 families, distributed into three orders, Entodiniomorphida, Macropodiniida, and Vestibuliferida. In recent years, trichostomatid ciliates have been playing a part in many relevant functional studies, such as those focusing in host feeding efficiency optimization and those investigating their role in the gastrointestinal methanogenesis, as many trichostomatids are known to establish endosymbiotic associations with methanogenic Archaea. However, the systematics of trichostomatids presents many inconsistencies. Here, we stress the importance of more taxonomic works, to improve classification schemes of this group of organisms, preparing the ground to proper development of such relevant applied works. We will present a historical review of the systematics of the subclass Trichostomatia highlighting taxonomic problems and inconsistencies. Further on, we will discuss possible solutions to these issues and propose future directions to leverage our comprehension about taxonomy and evolution of these symbiotic microeukaryotes.

Helmet-shaped Body of Entodiniomorphid Ciliates (Ciliophora, Entodiniomorphida), a Synapomorphy or a Homoplasy?

Triadinium was created to include Triadinium caudatum. Further, four other species were included, T. minimum, T. galea, T. elongatum, and T. magnum, all sharing a characteristic helmet-shaped body. Wolska and Grain argued that the inclusion of T. minimum and T. galea into Triadinium was done based on superficial morphological aspects, and established two new genera to accommodate these species: Circodinium and Gassovskiella. Although the phylogenetic relationships within Entodiniomorphida have been investigated by multiple authors, none of them discussed the evolutionary relationship of helmet-shaped entodiniomorphids. We performed molecular phylogenetics and revisited old literature digging for morphological data to explain our results. According to our analyses, the helmet-shaped body is homoplastic and may have evolved from at least three different entodiniomorphid ancestors. Circodinium minimum is phylogenetically related to members of Blepharocorythidae, T. caudatum emerged within Spirodiniidae and G. galea within Polydiniellidae. This phylogenetic hypothesis is partially supported by information on infraciliature and ultrastructure of C. minimum and T. caudatum. However, such morphological information is not available for polydiniellids. In order to shed some light into the evolution of the helmet-shaped ciliates, future works should focus to collect information on the infraciliature and the ultrastructure of Polydiniella mysorea and of other Triadinium species.

Phylogenetic Analyses Support Validity of Genus Eodinium (Ciliophora, Entodiniomorphida, Ophryoscolecidae)

The validity of genus Eodinium has been historically disputed due to morphological similarities with Diplodinium (absence of skeletal plates as well as adoral and dorsal ciliary zones at the same body level). To address this issue, the 18S rDNA of four Eodinium posterovesiculatum morphotypes and four Diplodinium anisacanthum morphotypes were sequenced and phylogenetically analyzed. The different inference methods suggest the existence of a last common ancestor of Eodinium and Ostracodinium that is not shared with Diplodinium, strongly supporting the validity of genus Eodinium. Since skeletal plates are present in all members of genus Ostracodinium, the most parsimonious is a secondary loss of skeletal plates in E. posterovesiculatum. This work represents a breakthrough in the taxonomy and phylogeny of the family Ophryoscolecidae indicating that the skeletal plates may not reflect evolutionary divergence within this group of ciliates as traditionally proposed.