A Case Study of the Morphological and Molecular Variation within a Ciliate Genus: Taxonomic Descriptions of Three Dysteria Species (Ciliophora, Cyrtophoria), with the Establishment of a New Species

Hui Zhang,Qianqian Zhang,Di Wu,Xiangrui Chen,Alan Warren,Xuetong Zhao,Zhishuai Qu

doi:10.3390/ijms23031764

Abstract

Three Dysteria species, D. crassipes Claparède & Lachmann, 1859; D. brasiliensis Faria et al., 1922; and D. paracrassipes n. sp., were collected from subtropical coastal waters of the East China Sea, near Ningbo, China. The three species were studied based on their living morphology, infraciliature, and molecular data. The new species D. paracrassipes n. sp. is very similar to D. crassipes in most morphological features except the preoral kinety, which is double-rowed in the new species (vs. single-rowed in D. crassipes). The difference in the small ribosomal subunit sequences (SSU rDNA) between these two species is 56 bases, supporting the establishment of the new species. The Ningbo population of D. crassipes is highly similar in morphology to other known populations. Nevertheless, the SSU rDNA sequences of these populations are very different, indicating high genetic diversity and potentially cryptic species. Dysteria brasiliensis is cosmopolitan with many described populations worldwide and four deposited SSU rDNA sequences. The present work supplies morphological and molecular information from five subtropical populations of D. brasiliensis that bear identical molecular sequences but show significant morphological differences. The findings of this study provide an opportunity to improve understanding of the morphological and genetic diversity of ciliates.

Highlights

Ciliates are single-celled eukaryotes that are highly developed, ubiquitous in freshwater, marine and terrestrial as biotopes, speciose, and morphologically diverse [1,2,3,4,5]
Introduction of silver staining methods provided recognition of ciliary patterns and nuclear morphology; these detailed structures allowed a better taxonomy of ciliates [6,16]
Body 45–60 × 30–35 μm in vivo, oval in outline with both ends rounded; four right kineties including two frontoventral kineties, innermost row commencing below cytostome and terminating at level of podite; four to eight left kineties, densely arranged near equatorial area; two parallel circumoral kineties almost equal in length; one double-rowed preoral kinety, kinetosomes obliquely arranged in front of cytostome; three left frontal kineties between preoral kinety and circumoral kineties; brackish water habitat

Summary

Introduction

Ciliates are single-celled eukaryotes that are highly developed, ubiquitous in freshwater, marine and terrestrial as biotopes, speciose, and morphologically diverse [1,2,3,4,5]. In the first 200 years, the taxonomic identifications or descriptions of ciliates were mainly based on living morphology. Their morphological features can sometimes reflect certain aspects of prevailing environmental conditions, such as food abundance and the presence of predators [8,9,10,11]. Taxa with similar or even identical morphology show highly divergent molecular information, while diverse morphotypes share the same molecular information. These anomalies have brought new controversies to ciliate research [12,17]

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