Techniques and tools for species identification in ciliates: a review

Abstract

Ciliates are highly divergent unicellular eukaryotic organisms with nuclear dualism and a highly specialized ciliary pattern. They inhabit all biotopes and play crucial roles in regulating microbial food webs as they prey on bacteria, protists and even on microscopic animals. Nevertheless, subtle morphological differences and tiny sizes hinder proper species identification for many ciliates. In the present review, an attempt has been made to elaborate the various approaches used by modern day ciliate taxonomists for species identification. The different approaches involved in taxonomic characterization of ciliates such as classical (using live-cell observations, staining techniques, etc.), molecular (involving various marker genes) and statistical (delimitation of cryptic species) methods have been reviewed. Ecological and behavioural aspects in species identification have also been discussed. In present-day taxonomy, it is important to use a 'total evidence' approach in identifying ciliates, relying on both classical and molecular information whenever possible. This integrative approach will help in the mergence of classical methods with modern-day tools for comprehensive species description in future.

Faunistic study on the freshwater ciliates from Delhi, India

“…Live cells were observed under high-power oil immersion objective with bright field, phase contrast and were complemented with protargol staining (Abraham et al 2019b) and Feulgen staining (Feulgen & Rossenbeck 1924;Gupta et al 2018). Measurements were done using eyepiece micrometer or measurement software with proper calibration.…”

“…And a few novel genera and species of ciliates have been reported from Delhi region (Arora et al 1999;Gupta et al , 2003Gupta et al , 2020Kamra et al 1994Kamra et al , 2008Kamra & Kumar 2010;Kaur et al 2019; Kumar et al 2015;Naqvi et al 2006Naqvi et al , 2016Singh & Kamra 2013. Knowledge of biodiversity of ciliates is becoming increasingly important for modelling and managing ecosystems as their significant role has become better known (Abraham et al 2019b;Basuri et al 2020; Dopheide et al 2008;Li et al 2010).…”

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

“…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].…”

Evolutionary Origin and Host Range of Plagiotoma lumbrici (Ciliophora, Hypotrichia), an Obligate Gut Symbiont of Lumbricid Earthworms

“…However, the majority of these alpha‐diversity data is based only on morphological observations and have not been tested by molecular methods, which can help to reveal the cryptic diversity or to detect misidentifications due to phenotypic plasticity (for a review, see Abraham et al. ).…”

“…On the other hand, astomes from earthworms represent a morphologically highly diverse and species-as well as genus-rich group accounting for about hundred taxa (for a review, see de Puytorac 1954de Puytorac , 1969de Puytorac , 1972. However, the majority of these alpha-diversity data is based only on morphological observations and have not been tested by molecular methods, which can help to reveal the cryptic diversity or to detect misidentifications due to phenotypic plasticity (for a review, see Abraham et al 2019).…”