Taxonomic And Phylogenetic Study Of Torrenticolidae From China

Torrenticolidae belongs to Lebertioidea,Trombidiformes,Acari,and is one of the most abundant groups in species diversity with the most distinctive morphological characteristics in water mites.Meanwhile,it also can be utilized as bioindicators in the survey of water quality of their sensitivity to water pollution.At present,there are still some critical scientific problems required to be solved quickly in torrenticolid water mite taxonomy,such as unbalanced regional research levels,limited available morphological characteristics,short of classification methods,and divergent views on phylogenetic relationships.As far as China is concerned,taxonomic research work of Torrenticolidae started relatively late.As of December 2016,there are only 13 torrenticolid species in China belonging to 3 subgenera,3 genera and 2 subfamilies were identified,occupying only 2.61% of the known species in the world.The species composition and faunal characteristics of Chinese fauna are still unclear,and there are still a large number of new taxonomic categories to be discovered.Therefore,it is of great significance to carry out research on the taxonomy of Torrenticolidae for making clear the species composition and their distribution in China fauna,and understanding the phylogenetic relationship of Torrenticolidae.It is a particularly important research especially in the context of global bioextinction.In this study,integrative taxonomy including morphological taxonomy,molecular phylogeny,geometric morphometrics were used to carry out comprehensive systematic taxonomy of Chinese torrenticolid mites.The main research contents and results are as following:1.Morphological classification researchBased on the morphological characteristics,82 torrenticolid species,belonging to6 subgenera,4 genera and 2 subfamilies,were identified from more than 1,800 samples from 20 provinces,municipalities and autonomous regions in China,including 1 new record genus,3 new record subgenus,59 new species(including 2species misidentified),and 8 new record species.And the proportion of Chinese torrenticolid mites has increased from 2.61% to 12.91% of known species from the whole world.Besides,a total of 521 specimen slides,190 feature plates(including more than 1,200 features),and 41 colour feature photographs were produced.At the same time,a key to the species,the genera and subgenera of Chinese Torrenticolidae were compiled.Details are as follows:(1)One new record genus to Chinese fauna: Neoatractides Lundblad,1941.(2)Three new record subgenera to Chinese fauna: Allotorrenticola(Cook,1967),Heteratractides(Lundblad,1941),Megapalpis Halbert,1944;(3)60 new species to science:(1)29 published species: Neoatractides proclusteroseta Gu & Guo,2018;Torrenticola acrisarostrum Gu & Guo,2019;Torrenticola aduncrostrum Gu & Guo,2019;Torrenticola anziensis Gu & Guo,2020;Torrenticola changbaiensis Gu & Guo,2019;Torrenticola fodingensis Gu & Guo,2018;Torrenticola hainanensis Gu & Guo,2019;Monatractides hamatapodemus Gu& Guo,2019;Torrenticola postfusina Gu & Guo,2019;Torrenticola pseudosiamis Gu& Guo,2020;Torrenticola lushanensis Gu & Guo,2020;Torrenticola planusorostruma Gu & Guo,2020;Torrenticola rectrostrum Gu,Jin & Guo,2020;Torrenticola songhuaensis Gu & Guo,2020;Torrenticola spinextension Gu & Guo,2019;Torrenticola suptilisrostrum Gu & Guo,2019;Torrenticola tenuichelicera Gu& Guo,2018;Torrenticola triextensio Gu & Guo,2019;Torrenticola trigona Gu &Guo,2019;Torrenticola wuyiensis Gu & Guo,2020;Torrenticola yunnanensis Gu,Jin& Guo,2020;Monatractides cuspiscoxer Gu & Guo,2019;Monatractides dingi Gu,Jin & Guo,2020;Monatractides jinni Gu & Guo,2019;Monatractides macrocorpis Gu & Guo,2019;Monatractides sichuanensis Gu & Guo,2020;Monatractides trilaminatus Gu & Guo,2020;Monatractides vietusacoxer Gu & Guo,2019;Monatractides xiaoxiensis Gu & Guo,2019;(2)31 new species to be published(including corrections of 2 misidentified species): Testudacarus sinensis sp.nov.,Torrenticola chelicerapodeme sp.nov.;Torrenticola fusiformis sp.nov.;Torrenticola exiguusipalpi sp.nov.;Torrenticola euryides sp.nov.;Torrenticola pseudosemicolor sp.nov.(Originally identified as Torrenticola semicolor Viets K.O.,1977);Torrenticola gladiusirostrum sp.nov.;Torrenticola obrimo sp.nov.;Torrenticola apsentisprojection sp.nov.;Torrenticola pseudoalargada sp.nov.(Originally identified as Torrenticola alargada Goldschmidt,2007);Torrenticola heteroides sp.nov.;Torrenticola longavirisa sp.nov.;Torrenticola yii sp.nov.;Torrenticola brunusum sp.nov.;Torrenticola brevisuturae sp.nov.;Monatractides cylindrapodeme sp.nov.;Torrenticola digitusa sp.nov.;Monatractides pseudopinapalpis sp.nov.;Torrenticola wuae sp.nov.;Torrenticola rectuschelicera sp.nov.;Monatractides globosus sp.nov.;Torrenticola longsutura sp.nov.;Torrenticola luodianensis sp.nov.;Monatractides rotundalamina sp.nov.;Monatractides polusamargin sp.nov.;Monatractides multiplicisetae sp.nov.;Monatractides ambyoatus sp.nov.;Torrenticola lateralisprojectura sp.nov.;Torrenticola proprirostrum sp.nov.;Torrenticola rectognatha sp.nov.;Torrenticola repandorostrum sp.nov..(4)Nine new record species to Chinese fauna: Neoatractides malayensis(Wiles,1991);Torrenticola dentifera Wiles,1991;Torrenticola distans Viets K.O.,1981;Torrenticola neoungeri Pe?i?,Asadi & Smit,2019;Torrenticola nipponica(Enami,1940);Torrenticola siamis Pe?i? & Smit,2009;Torrenticola turkestanica(Sokolow,1926);Monatractides macrognatha(Viets K.,1935);Monatractides tuzovskyi Pe?i?,Kumar N.,Kumar K.& Kumar S.,2006.2.Analysis of Chinese faunal characteristicsThis research work analysed in detail the distribution of Chinese torrenticolid species and discussed their distribution types and faunal characteristics in zoogeographic divisions of the world and China,using the statistical method of every unitary pattern and accumulated patterns.The results showed that among 82 species of Torrenticolidae in China,63 species(76.83%)belong to the Oriental pattern only,and 74 species(90.24%)belong to the Oriental and accumulated patterns containing the Oriental.Thus,Chinese fauna of Torrenticolidae is the Oriental typically.In zoogeographic divisions of China,there are 43 species(52.43%)distributed in Central China Region only,and 52 species(63.41%)distributed in Central China and accumulated patterns containing Central China.Therefore,Chinese fauna of Torrenticolidae is Central China type.From the accumulated patterns,accumulated species numbers and accumulated proportions of Chinese torrenticolid mites with specified realm in zoogeographic region of the world,the Chinese fauna of Torrenticolidae has the strongest lineage with the Palearctic Realm,followed by African Realm,and there are only weak lineages with Nearctic Realm,Australian Realm,Neotropical Realm.In zoogeographic divisions of China,it has the strongest lineage with South China Region,followed by North China Region,and there is only weak lineage with Southwest Region,Qinghai-Tibet Region and Inner Mongolia-Xinjiang Region.3.Phylogeny research based on morphological charactersA phylogenetic analysis of Torrenticolidae was performed with 37 adult external morphological characters from 83 species in 11 subgenera,7 genera using the method of maximum parsimony by software TNT 1.5,and the Sperchon grigorievka Pe?i? &Smit,2020 was selected as the outgroup.The results supported the nowaday classification system of 11 subgenera,7 genera,2 subfamilies of Torrenticolidae.And their phylogenetic relationship is:(Testudacarus + Debsacarus)+((Monatractides +Pinquicola)+(Stygotorrenticola +((Torrenticola + Megapalpis)+((Allotorrenticola+(Heteratractides + Neoatractides))+ Pseudotorrenticola)))).4.Molecular phylogeny of Torrenticolidae from ChinaIn this study,two target gene fragments,COI and 28 S r DNA,were selected to explore the phylogeny relationship of Torrenticolidae,with the methods of Maximum Likelihood(ML)and Bayesian(BI)to construct its phylogenetic tree.The results of the single gene and combined gene trees all supported the monophyleticity of Testudacarinae and Torrenticolinae,and further verified the accuracy of the present classification system of 2 subfamilies of Torrenticolidae and 2 genera of Testudacarinae,which are consistent with the results of phylogenetic analysis of morphological characteristics.At the same time,it was clarified that the average genetic distance among species based on the COI gene of Torrenticolidae was 0.192,and 0.262 based on the 28 S r DNA gene.5.Geometric morphometricsThe morphological variations of features including Gland position of dorsoglandularia 1–4,the anterior margins of coxae,and infracapitulum in 129 torrenticolid mites,and gland position of ventroglandularia 1–4 in 88 torrenticolid mites were analyzed by the method of geometric morphometrics.And the variability trends of the above characteristics were clarified.At the same time,the differences of those features mentioned above between genera,subgenera and similar species were analyzed.And the results showed that there were varying degrees of differences between the genera,subgenera and similar species,which can be used as classification features available for the classification of Torrenticolidae.In summary,the results above showed that the anterior margins of coxae,infracapitulum,gland position of dorsoglandularia 1–4 and ventroglandularia 1–4 can be utilized to distinguish genera,subgenera and species of Torrenticolidae,which shows that geometric morphometrics can effectively distinguish Torrenticolidae rapidly and accurately,as a new method for the study of Torrenticolidae taxonomy.