Shedding light on the polyphyletic behavior of the genus Sterkiella: The importance of ontogenetic and molecular phylogenetic approaches.

Daizy Bharti,Komal Kamra,Antonietta La Terza,Govindhasamay R Varatharajan,Santosh Kumar

doi:10.1371/journal.pone.0207688

Daizy Bharti, Komal Kamra + Show 3 more

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https://doi.org/10.1371/journal.pone.0207688

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Abstract

Present study, investigates a poorly known species of the genus Sterkiella, i.e., S. tricirrata, based on two populations isolated from soil samples collected from the Colfiorito Regional Park, Umbria Region, Italy and from the Silent Valley National Park, India. Both populations showed a highly similar morphology, however different ontogenetic pattern in between. The study confirms the validity of the species S. tricirrata which was considered to be a species within the Sterkiella histriomuscorum complex. The main ontogenetic difference between S. tricirrata and other species of the genus Sterkiella is the different mode of formation of anlagen V and VI of the proter in the former. In the phylogenetic analyses, Sterkiella tricirrata clusters with Sterkiella sinica within the stylonychine oxytrichids, in a clade away from the type species (Sterkiella cavicola) of the genus Sterkiella. The study highlights the importance of ontogenetic as well as molecular data in shedding light on the polyphyletic behavior of the genus Sterkiella. A detailed description of S. tricirrata based on morphology, ontogenesis and molecular phylogenetic methods is presented. Further, the improved diagnosis has been provided for the genus Sterkiella and the poorly known species S. tricirrata.

Highlights

Recent studies, among the hypotrich and spathidiid ciliates, have shown that detailed observations of characters often resolve the discrepancy between the morphological and molecular analyses [1,2,3,4]
Comparison of Sterkiella tricirrata with related species and populations Sterkiella tricirrata can be compared with species of the genus Sterkiella having two macronuclear nodules, i.e., Sterkiella histriomuscorum (Foissner et al, 1991) Foissner, Blatterer, Berger & Kohmann, 1991; S. nova Foissner & Berger, 1999; S. subtropica Chen et al, 2015; S. sinica Chen et al, 2016, and S. ecuadoriana Foissner & Heber in Foissner, 2016
This, supports the validity of Sterkiella tricirrata at species rank and out of the S. histriomuscorum complex; this separation is in agreement with Kumar et al [1], who described a novel Sterkiella species with four macronuclear nodules mainly on the basis of four transverse cirri

Summary

Introduction

Among the hypotrich and spathidiid ciliates, have shown that detailed observations of characters often resolve the discrepancy between the morphological and molecular analyses [1,2,3,4]. This reiterates the need for an integrated approach to investigate in-depth ciliate diversity [5]. The identification of cryptic characters among hypotrich ciliates (e.g. cyst structures, morphology, details on the mode of division) has justified the separation of morphologically similar species reflecting distant relationships in molecular phylogeny [3, 6,7,8,9].

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