Using DNA Composite Barcode Technology To Study Zooplankton Diversity In Sanmenxia Reservoir

Zooplanktons are a series of extremely complicated heterotrophic aquatic animals that suspend in water and are weak in swimming or incapable of swimming.Zooplanktons in fresh water mainly include protozoons,rotifers,copepods and cladocera.They are fed with phytoplanktons,bacteria and debris.Meanwhile they are hunt by other aquatic animals,which play an important role in material circulation and energy flow water ecosystem.Traditional classification strategies are time-consuming and less accurate.Therefore,DNA metabarcoding,a technique based on next-generation genetic sequencing was introduced to identify species in environmental samples.Sanmenxia reservoir,an important habitat of rare birds in China,contains various species of aquatic organisms.Studies on biodiversity of zooplanktons based on DNA metabarcoding technique have not yet been conducted before.Water and zooplankton samples were collected in July and October,2017,January and April,2018 from 9 sites of Sanmenxia reservoir,respectively.18S rRNA and COI sequences were selected as molecular markers.By using DNA metabarcoding technique,systematic study on biodiversity of aquatic organisms was conducted.The aim of this research mainly focus on obtaining the preliminary information about the composition zooplankton community and key ecological factors that influence the seasonal variation of zooplanktons.The main results are as follows:(1)The amplicons of 18S rRNA gene were sequenced on an Illumina MiSeq PE250 platform.3245439 high quality sequences were obtained after quality control,pair-end assembly and filtering.334 OTUs were obtained via cluster and annotation,131 of which were annotated as zooplanktons.Using the same method,2028940 high quality sequences of COI amplicons were obtained,resulting in 512 OTUs and 188 of them were annotated as zooplanktons.(2)Results on community structure:Fauna composition:Classification via 18S rRNA revealed a result of 131 species in 82 families,which include 95 species of protozoons,13 species of rotifers,19 species of copepods and 4 species of cladocera.Classification via COI showed a result of 188 species in 83 families,which include 31 species of protozoons,83 species of rotifers.45 species of copepods and 29 species of cladocera.The combined result of 18S RNA and COI showed a result of 311species in 150 families,which include 126 species of protozoons,90 species of rotifers,60 species of copepods and 32 species of cladocera.The results suggested that in Sanmenxia reservoir,protozoons and rotifers are more abundant than copepods and cladocera.Seasonal distribution:Based on 18S rRNA analysis,in spring,summer,autumn and winter,58,92,82 and 76 species of zooplanktons were classified,respectively.Based on COI analysis,in spring,summer,autumn and winter,101,132,151and 89 species of zooplanktons were classified,respectively.The combined result showed that there were 156,219.229 and 161 species of zooplanktons in spring,summer,autumn and winter,respectively.The results indicated a higher percentage of zooplantons in summer and autumn,compared with spring and winter.Change of abundance:Copepoda and rotiferas in Sanmenxia reservoir showed a relatively high abundance,while protozoons and cladocera showed a relatively low abundance.(3)Analysis on biodiversity:Both biodiversity and abundance of zooplankton showed a significant seasonal variation.Both showed a higher percentage in summer and autumn,compared with spring and winter.(4)Cluster analysis showed that the community structure of winter and spring are similar and greatly different from that in summer.(5)Canonical correspondence analysis:water temperature,total nitrogen,pH and ammonia nitrogen are the key ecological factors that influe(6)nce the community structure of zooplanktons in Sanmenxia reservoir.The community structure in spring is closely related to total nitrogen and total phosphorus.The community structure in summer is closely related to water temperature and chemical oxygen demand.The community structure in autumn is closely related to water temperature and total nitrogen.The community structure in winter is closely related to ammonia nitrogen.