Biogeography and Character Evolution of the Ciliate Genus Euplotes (Spirotrichea, Euplotia), with Description of Euplotes curdsi sp. nov.

Mitchell J Syberg-Olsen,Vittorio Boscaro,Patrick J Keeling,Claudia Vannini,Nicholas A T Irwin,Fabrizio Erra,Graziano Di Giuseppe,Michael Schubert

doi:10.1371/journal.pone.0165442

Mitchell J Syberg-Olsen, Vittorio Boscaro + Show 6 more

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https://doi.org/10.1371/journal.pone.0165442

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Abstract

Ciliates comprise a diverse and ecologically important phylum of unicellular protists. One of the most specious and best-defined genera is Euplotes, which constitutes more than 70 morphospecies, many of which have never been molecularly tested. The increasing number of described Euplotes taxa emphasizes the importance for detailed characterizations of new ones, requiring standardized morphological observations, sequencing of molecular markers and careful comparison with previous literature. Here we describe Euplotes curdsi sp. nov., distinguishable by the combination of the following features: 45–65 μm length, oval or elongated shape with both ends rounded, narrow peristome with 25–34 adoral membranelles, conspicuous paroral membrane, double-eurystomus dorsal argyrome type, 6–7 dorsolateral kineties and 10 frontoventral cirri. Three populations of the novel species have been found in brackish and marine samples in the Mediterranean and the White Sea. We provide the SSU rRNA gene sequences of these populations, and an updated phylogeny of the genus Euplotes. Using the molecular phylogenetic tree, we inferred aspects of the biogeographical history of the genus and the evolution of its most important taxonomic characters in order to provide a frame for future descriptions. Ultimately, these data reveal recurrent trends of freshwater invasion and highlight the dynamic, yet convergent, morphological evolution of Euplotes.

Highlights

Ciliates are ubiquitous, abundant and eyecatching components of aquatic environments [1,2,3,4]
Specimens were characterized using a combination of differential interference contrast (DIC) microscopy, silver nitrate staining (Chatton-Lwoff method [39]), Feulgen staining, fluorescent microscopy of DAPI stained living and fixed cells and scanning electron microscopy (SEM)
The paroral membrane is conspicuous in silver stained specimens (Fig 2G), but the corresponding cilia rarely protrude outside the buccal cavity (Fig 2I)

Summary

Introduction

Ciliates (unicellular protists of the phylum Ciliophora) are ubiquitous, abundant and eyecatching components of aquatic environments [1,2,3,4]. Despite their large diversity and ecological importance, only a handful of ciliates have been intensively studied after their original description. These model species, including those belonging to the genera Paramecium [5,6,7] and Tetrahymena [8,9,10], are easy to grow under laboratory conditions and relatively common.

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