Pleurostomatid ciliates,as a highly diverse and widely distributed unicellular eukaryote group,play a crucial role in the cycling of nutrients and energy in microbial food webs.However,research on pleurostomatids remains insufficient,resulting in a paucity of molecular information and substantial gaps in knowledge of their phylogenetic relationships.In recent years,we investigated pleurostomatid diversity in various Chinese habitats,including their systematic relationships and taxonomic circumscriptions,which were comprehensively analyzed using an integrative morphomolecular approach.Results revealed that:(1)pleurostomatids can be categorized into two suborders,Protolitonotina subord.nov.and Amphileptina Jankowski,1967;(2)Protolitonotina subord.nov.represents the ancestral pleurostomatid group and includes two genera,Protolitonotus and Heterolitonotus gen.nov.,characterized by right kineties progressively shortened along rightmost full kineties and absence of a left dorsolateral kinety;(3)Heterolitonotus gen.nov.represents an orphan lineage and is defined by an oral slit extending to its dorsal margin;(4)“Protolitonotus clampi”does not group with congeners but instead represents an orphan lineage,thus Novilitonotus gen.nov.is established to which P.clampi is transferred as Novilitonotus clampi comb.nov.;(5)three new species,Apoamphileptus paraclaparedii sp.nov.,Heterolitonotus rex gen.nov.,sp.nov.,and Loxophyllum apohelus sp.nov.,are described;and(6)helices 21es6a to 21es6d within the V4 region of small subunit ribosomal RNA(SSU rRNA)may serve as a useful tool for discriminating pleurostomatids.The evolutionary relationships among all main lineages of pleurostomatids are discussed and a key to the identification of pleurostomatid genera is provided.
Meiotic recombination is essential for sexual reproduction and its regulation has been extensively studied in many taxa.However,genome-wide recombination landscape has not been reported in ciliates and it remains unknown how it is affected by the unique features of ciliates:the synaptonemal complex(SC)-independent meiosis and the nuclear dimorphism.Here,we show the recombination landscape in the model ciliate Tetrahymena thermophila by analyzing single-nucleotide polymorphism datasets from 38 hybrid progeny.We detect 1021 crossover(CO)events(35.8 per meiosis),corresponding to an overall CO rate of 9.9 cM/Mb.However,gene conversion by non-crossover is rare(1.03 per meiosis)and not biased towards G or C alleles.Consistent with the reported roles of SC in CO interference,we find no obvious sign of CO interference.CO tends to occur within germ-soma common genomic regions and many of the 44 identified CO hotspots localize at the centromeric or subtelomeric regions.Gene ontology analyses show that CO hotspots are strongly associated with genes responding to environmental changes.We discuss these results with respect to how nuclear dimorphism has potentially driven the formation of the observed recombination landscape to facilitate environmental adaptation and the sharing of machinery among meiotic and somatic recombination.
Lu FuChen GuKazufumi MochizukiJie XiongWei MiaoGuangying Wang
The inland saltwater lakes harbor exceptional biodiversity.Here,two new species of solitary sessile peritrich ciliates were isolated from Qinghai Lake,the largest inland saltwater lake in China.Their morphology,ciliature,silverline system,and molecular phylogeny were investigated based on live observation,silver staining,and analysis of the small subunit ribosomal DNA(SSU rDNA).Vorticella paraglobosa sp.n.is characterized mainly by its obconical or elongate bell-shaped zooid,C-shaped macronucleus,single ventrally located contractile vacuole,two-rowed infundibular polykinety 3,and 28-38 silverlines between peristome and aboral tro-chal band and 10-15 between aboral trochal band and scopula.Vorticella cotyliformis sp.n.differs from its congeners mainly by its double-layered peristomial lip,cup-shaped zooid,J-shaped macronucleus,single ventrally positioned contractile vacuole,three-rowed infundibular polykinety 3,and 70-85 silverlines between peristome and aboral trochal band and 21-25 between aboral trochal band and scopula.The SSU rDNA sequences of the two new species were obtained,and the subsequent molecular phylogenetic analysis supported their taxonomic classification.
Species of the ciliate class Heterotrichea Stein,1859 are a cosmopolitan group of unicellular eukaryotic microorganisms,many of which have been widely used as models in various fields of research such as regenerative biology,functional ecol-ogy,environmental toxicology,and symbiotic behavior.However,species identification in the heterotrich family Condylos-tomatidae,especially the most species-rich and type genus Condylostoma Bory de Saint-Vincent,1824,remains challenging due to incomplete original descriptions,few reliable distinguishing characters,and overlapping features between different species.This study presents an updated revision of Condylostoma and its related genus Condylostomides da Silva Neto,1994 based on descriptions of five species,including nine populations collected from China,using both morphological and molecular methods.The main findings are as follows:(1)43 nominal species and about 130 populations are reviewed,result-ing in the recognition of 30 valid species of Condylostoma and eight valid species of Condylostomides;(2)keys,synonyms,biogeographic distributions and amended/improved diagnoses of all valid species are provided;(3)based on the available data,four new Condylostoma species(C.marinum sp.nov.,C.petzi sp.nov.,C.villeneuvei sp.nov.,and C.microstomum sp.nov.),one new combination(Condylostomides minimus(Dragesco,1954)comb.nov.&nom.corr.),and two corrected names(Condylostoma ancestrale Villeneuve-Brachon,1940 nom.corr.and Condylostomides nigrus(Dragesco,1960)nom.corr.)are suggested;(4)cryptic species are detected and proposed for the first time to form the Condylostoma curvum spe-cies complex;(5)three highly confusing Condylostoma species,C.kris,C.spatiosum,and C.minutum,are redefined for the first time based on modern taxonomic methods;(6)a‘flagship’species,Condylostomides coeruleus,is recorded for the first time from the continent of Asia,substantially expanding its biogeography;(7)ciliature adjacent to the distal end of the paroral membrane within the family Condylostomatidae is
Aquaculture of red swamp crayfish Procambarus clarkii is an emerging farming industry in China.As shown recently,one of the most significant diseases affecting the red swamp crayfish is caused by overabundance of epibiotic peritrichs,a group of ciliated protists that are commonly found living as epibionts on aquatic animals.Nevertheless,few studies focusing on this issue have been performed.As part of a faunal study carried out in the Lake Weishan Wetland,China,four colonial sessilid peritrichs,namely Epicarchesium granulatum,Epistylis bimarginata,Epistylis semiciculus,and Zoothamnium procerius,attached to P.clarkii are documented.For each species,redescriptions and improved diagnoses are supplied.As a further aid to identification,14 new rDNA sequences of these four and a closely related species were obtained.In addition,as an aid for future studies on epibiotic ciliates,we supply a list and information about recent integrative studies that document the geographic distributions of related taxa.