Biodiversity of freshwater ciliates (Protista, Ciliophora) in the Lake Weishan Wetland, China: the state of the art

Abstract

Ciliates are core components of the structure of and function of aquatic microbial food webs. They play an essential role in the energy flow and material circulation within aquatic ecosystems. However, studies on the taxonomy and biodiversity of freshwater ciliates, especially those in wetlands in China are limited. To address this issue, a project to investigate the freshwater ciliates of the Lake Weishan Wetland, Shandong Province, commenced in 2019. Here, we summarize our findings to date on the diversity of ciliates. A total of 187 ciliate species have been found, 94 of which are identified to species-level, 87 to genus-level, and six to family-level. These species show a high morphological diversity and represent five classes, i.e., Heterotrichea, Litostomatea, Prostomatea, Oligohymenophorea, and Spirotrichea. The largest number of species documented are oligohymenophoreans. A comprehensive database of these ciliates, including morphological data, gene sequences, microscope slide specimens and a DNA bank, has been established. In the present study, we provide an annotated checklist of retrieved ciliates as well as information on the sequences of published species. Most of these species are recorded in China for the first time and more than 20% are tentatively identified as new to science. Additionally, an investigation of environmental DNA revealed that the ciliate species diversity in Lake Weishan Wetland is higher than previously supposed.

Supplementary information: The online version contains supplementary material available at 10.1007/s42995-022-00154-x.

Keywords: Environmental DNA; Protozoa; Species diversity; Taxonomy.

Fig. 1

Sampling sites and habitat characteristics in Lake Weishan Wetland. The insert figure of partial part of China (upper right) indicates the location of Lake Weishan Wetland

Fig. 2

A The variations of surface water temperature, electrical conductivity (EC) and OTU richness of Ciliophora (plankton community) from August 2020 to July 2021. B The variations of nitrate (NO₃⁻), pH and dissolved oxygen concentration (DO) from August 2020 to July 2021. C Temporal variations in the plankton community composition of Ciliophora based on the rank of order from August 2020 to July 2021

Fig. 3

The species distributions of the investigated groups. A The investigated groups. The leaves represent the families included in each group, and the different sizes of leaves represent different values of species number in each family. B, C Species distributions at order-level. D species distributions at family-level

Fig. 4

Selected heterotrichous ciliates found in Lake Weishan Wetland (original). A Spirostomum teres, arrowhead indicates the contractile vacuole, arrow indicates the macronucleus. B Stentor coeruleus. C Climacostomum virens, arrowheads indicate the cyrtos, arrow indicates the contractile vacuole. D, E Blepharisma sp., arrowheads indicate the cortical granules, arrows indicate the paroral membrane, double arrowheads indicate the adoral zone of membranelles. F Linostomella pseudovorticella. G Oral infraciliature of Stentor coeruleus. H Stentor spp., arrowheads indicate Stentor roeselii, arrows indicate Stentor coeruleus. I Stentor roeselii, arrow indicates the contractile vacuole. J Cortical granules (arrowheads) of Climacostomum virens. K Cortical granules (arrowheads) of Stentor roeselii. L Cortical granules (arrowheads) of Stentor coeruleus. M General infraciliature of Stentor coeruleus adjusted by the invert function via Photoshop. Ma Macronucleus. Scale bars 50 μm (C), 100 μm (A, D, F, I), 300 μm (B, H, M)

Fig. 5

Selected haptorid (A–H, J–L) and prorodontid (I, M–P) ciliates found in Lake Weishan Wetland (original). A, B Pseudomonilicaryon spp., arrowheads indicate the proboscis, arrow indicates the oral opening. C, J, K Enchelyotricha spp., arrow in J indicates the contractile vacuole, arrow in K indicates the oral bulge. D, E Paradileptus sp., arrows in D indicate the contractile vacuoles, arrow in E indicates the oral opening, arrowhead in E indicates the proboscis. F Trachelius ovum, arrow indicates the proboscis. G Didinium sp. H Homalozoon sp. I, O, P Holophrya sp. after protargol staining (I), in vivo (O), and after dry silver nitrate staining (P), arrow indicates the brosse, arrowhead indicates the oral opening. L Kamburophrys sp. M, N Coleps sp. in vivo (M) and after protargol staining (N), arrows indicate the spines. Scale bars 60 μm

Fig. 6

Selected pleurostomatid ciliates found in Lake Weishan Wetland. A Amphileptus sp. B–E Kentrophyllum spp., white arrows indicate the macronuclear nodules, red arrows indicate the contractile vacuoles. F Loxophyllum sp. G, N, P Amphileptus weishanensis, arrows in (P) indicate the macronuclear nodules. H, I Amphileptus sp., white arrows indicate the macronuclear nodules. J, L Protolitonotus sp. K Litonotus sp. M Amphileptus parapleurosigma. O Amphileptus sp., red arrow marks the extrusomes. Scale bars 100 μm (A, H, I, J, L–N), 75 μm (B–F), 200 μm (G, P), 50 μm (K), 60 μm (O)

Fig. 7

Selected peniculids and scuticociliates found in Lake Weishan Wetland (original). A Paramecium sp., arrow indicates the caudal cilia. B Frontonia sp., arrow indicates the buccal cavity, arrowhead indicates the postoral suture. C Myxophyllum sp. D, E Glauconema sp. after silver nitrate (D) and protargol staining (E), arrows in D indicate the contractile vacuole pores, arrow in E indicates the caudal complex. F Marituja sp. G Pleuronema sp., arrow indicates the paroral membrane. H Dexiotricha granulosa, arrow indicates the caudal cilium. I, J, N Lembadion lucens in vivo (I), after silver nitrate staining (J) and after protargol staining (N), arrow in (I) indicates the buccal cavity, arrow in (N) indicates macronucleus. K Cyclidium sp. L, M Uronema nigricans, in vivo (L) and after wet silver nitrate staining (M, image processed by the invert function via Photoshop). O Lembadion bullinum. Abbreviation: Ma, Macronucleus. Scale bars 100 μm (A, B, F), 40 μm (C), 30 μm (G, I, J, N), 20 μm (H), 10 μm (K–M), 70 μm (O)

Fig. 8

Selected peritrich ciliates found in Lake Weishan Wetland. A, H, P Epistylis spp. B Ophrydium crassicaule. C Campanella umbellaria. D Protargol-stained zooid of Epistylis hentscheli. E, F Vorticella spp. G Epicarchesium sinense, arrows mark the discontinuous spasmoneme. I Campanella sinica. J Dry silver nitrate-stained zooid of Epicarchesium granulitum, arrow marks the trochal band. K, O Pyxicola carteri, arrow marks the operculum, arrowhead marks the tube in lorica base. L Opercularia nutans. M Part of oral ciliature of Carchesium polypinum (image processed by the invert function via Photoshop). N Zoothamnium arbuscula. Q Opercularia sp. Scale bars 200 μm (A, B), 150 μm (G), 80 μm (H, I), 30 μm (K, L), 40 μm (O), 70 μm (P), 30 μm (Q)

Fig. 9

Selected parasitic/epibiotic peritrich ciliates found in Lake Weishan Wetland (original). A–D Epistylis spp., arrows indicate the zooids. E Trichodina pediculus (arrows) on Hydra sp. F Adhesive disk of Trichodina nobillis. G, K Carchesium cyclopidarum, protargol-stained specimen in G, arrows in K indicate colonies attached to the host. H Lagenophrys (?) sp. (arrows). I Adhesive disk of Trichodina sp. (after dry silver nitrate staining). J Trichodina sp. (arrows) on skin of a fish. Scale bars 0.5 cm in A; 100 μm (B); 60 μm (C, D); 20 μm (F, J)

Fig. 10

Selected hypotrichous ciliates found in Lake Weishan Wetland (original). A Cyrtohymena primicirrata. B Pleurotricha curdsi. C, J Stichotricha sp. D, E Kerona pediculus in vivo (D) and after protargol staining (E, image processed by the invert function via Photoshop). F Cortical granules of Pseudokeronopsis erythrina. G Euplotes muscicola. H Detail of silverline system on dorsal side of Euplotes sp. I Urosoma caudata. K, L Chaetospira sp. in vivo (K) and after protargol staining (L) Scale bars 50 μm (A, B, D, I–L), 20 μm (G)