Biodiversity And Distribution Pattern Of Genus Baetis In Headwater Streams Of The Ili River

The Ili River originates from the Tianshan Mountains in Xinjiang and flows into the Balkhash Lake in Kazakhstan.The length of the Ili River in China is 442 km.The Tianshan Mountains are rich in glacier and snow resources.Under the background of global warming,the headwater streams of Ili River,regulated by glaciers and snow,exhibit very sensitive and fragile to external changes.Changes in meltwater characteristics lead to changes in the spatial and temporal distribution of the water environment and frequent extreme events,which affect biodiversity to different degrees.Many species of the genus Baetis were found in these highaltitude and low-temperature aquatic habitats.Species of the genus Baetis are sensitive to environmental changes and spend most of their life history in the aquatic stage(nymphal stage).And they are also important indicator species for the health of headstream ecosystems and are the most abundant but difficult to identify among Ephemeroptera.In this study,we aimed to investigate the species compositions,phylogenetic status,key habitat factors,and historical and current factors of population differentiation and distribution changes of genus Baetis species in the headwater streams of the Ili River.In this study,samples were collected from the headwater streams of the Ili River in the Tianshan Mountains from 2018 to 2021.Five new species and one new record species of Baetis from the Tianshan Mountains,China were identified by morphological observation and molecular phylogenetic analysis based on COI gene.According to morphological identification,the antennae of these Baetis have stout setaes and the dorsal surface of the abdomen have scales.The K2 P genetic distance between five new species and Rhodobaetis subgenus was 0.2150 ± 0.0180～0.2293 ± 0.0190,which was close to the K2 P genetic distance within the Rhodobaetis subgenus 0.2272 ± 0.0171.At the same time,BI and ML phylogenetic tree results also showed that all the five new species clustered within the Rhodobaetis subgenus,so that all the five new species belonged to the Rhodobaetis subgenus.The five new species were named as: Baetis(Rhodobaetis)tianshanensis sp.nov.,Baetis(Rhodobaetis)yuwei sp.nov.,Baetis(Rhodobaetis)tekesiensis sp.nov.,Baetis(Rhodobaetis)mengketensis sp.nov.,Baetis(Rhodobaetis)tuergenensis sp.nov.;and one new recored species was Baetis(Rhodobaetis)braaschi Zimmermann 1980.Habitat conditions can affect the growth and development,distribution characteristics and genetic diversity of organisms.To explore the effects of environmental and geographical factors on the population structure and genetic diversity of six species of Baetis in Tianshan,Xinjiang.In April 2021,samples were collected from 27 headwater streams of the Ili River.It was found that environmental factors(water depth,river width,velocity,water temperature,dissolved oxygen,electrical conductivity,turbidity and p H)showed a downward trend with the increase in altitude.The most significant environmental factors affecting the population density of Baetis were water temperature,and electrical conductivity(P < 0.05),and significant geographical factors were altitude and latitude(P < 0.05).Environmental and geographical factors had different effects on the genetic diversity of six Baetis species.In general,electrical conductivity significantly affects the genetic diversity of Baetis(P < 0.05).At the same time,isolated by high mountains,Baetis species also showed that genetic distance increases with geographic distance.B.(R.)tianshanensis,B.(R.)mengketensis and B.(R.)tekesiensis were better adapted to the low temperature and high-altitude aquatic environment.B.(R.)tuergenensis and B.(R.)braaschi were mainly found in the headwater streams at lower elevations.B.(R.)yuwei was the most widely distributed in the headwater streams of the Ili River.B.(R.)yuwei,B.(R.)tianshanensis,B.(R.)tekesiensis and B.(R.)mengketensis prefer clean water and were sensitive to changes in water quality.The study of molecular systems geography showed that multiple COI gene haplotypes were detected in six Baetis species,indicating different degrees of genetic diversity.Based on the phylogenetic analysis of Bayesian inference and Maximum likelihood method and TCS haplotype network showed that B.(R.)yuwei population was divided into four branches(Clade A1～4);B.(R.)mengketensis population was divided into four branches(Clade B1～4);B.(R.)tekesiensis population was divided into four branches(Clade C1～4);the B.(R.)tianshanensis population was only one branch(Clade D);B.(R.)tuergenensis population was divided into two branches(Clade E1,E2);and B.(R.)braaschi(Clade F).The divergence times showed that,except for B.(R.)braaschi,which diverged during the Middle Pleistocene of the Quaternary,the other five Baetis species also diverged during the early Pleistocene of the Quaternary.In the history of the Ili River Valley in the Tianshan Mountains,species of Baetis were widely distributed and had gene communication among populations.However,after the late Tertiary,tectogenesis(ground uplifting to form mountains and subsidence to form basins),climate change,and glaciers have strongly altered the habitat of Baetis.Many geographic populations divided by mountains and basins.Although the populations of some species are geographically isolated,geographical haplotype groups have not yet been formed.Even the widespread species B.(R.)braaschi has the same haplotype distribution in the Altai and Tianshan Mountains of Xinjiang.Finally,the Geographic Information System(GIS)and Maximum Entropy model(Max Ent)were used to predict potentially suitable areas of Baetis species in Xinjiang province during current climatic data(1970～2000),Mid Holocene(6000 years ago,MH),Last Glacial Maximum(22,000 years ago,LGM),and Last interglacial(120,000～140,000 years ago,LIG),based on Baetis species sample sites and environmental data.The results showed that from the LGM to the MH,the suitable area gradually expanded and then retreated to the lowest historical trend in the current climate of B.(R.)yuwei,B.(R.)mengketensis,B.(R.)tekesiensis and B.(R.)tuergenensis.However,the trend of the suitable area shrinking from the LIG to the LGM,expanding in MH,and then shrinking to the lowest level in the current climate of B.(R.)tianshanensis and B.(R.)braaschi.Baetis of the headwater streams of the Ili River prefer to live in cold flowing water habitats.Since the LIG,Baetis has been restricted by historical climate and glacier changes,and its refuge was mainly distributed in mountainous headwater streams with high elevations.In conclusion,this study identified the species,distribution,phylogenetic status,and key factors affecting the population and genetic diversity of the species of genus Baetis in the headwater streams of the Ili River,Tianshan Mountains,China.In addition,this study explained the factors affecting the differentiation and distribution of Baetis species based on historical and current geological and climatic characteristics.This study may provide theoretical and data support for aquatic species resource data and biodiversity conservation of insects in high-latitude mountains and rivers in the Tianshan Mountains.