Phylogeny And Origin Study Of Marine Chironomid(Diptera:Chironomidae) Along The Eastern And Southern Coasts Of China

Marine chironomids is a group of chironomids living in the intertidal zone.Its life cycle is highly homologous with the tidal rhythm and the moon cycle.There are two main hypotheses about the origin of marine chironomids: the primitive hypothesis and the secondary hypothesis.At present,there are nearly 30 genera and more than 100 species of marine chironomids recorded around the world,but only 9 genera and 14 species are recorded in China.At present,there is no comprehensive taxonomic study on marine chironomids in China through the integrated model of morphology and molecular biology.In order to explore the biodiversity of chironomid in the eastern and southern coasts of China and study the phylogenetic relationship of marine chironomids and to evaluate the time of divergence of its main populations.This study carried out a study on the biological systematics of marine chironomids from 21 sites from the Yellow Sea,the East China sea and the South China Sea.Based on 593 gene sequences(COI-3P,COI-5P,18 S,28S,CAD1 and CAD4),the phylogenetic tree of marine chironomids was reconstructed by using maximum likelihood method and Bayesian inference method.Based on 453 gene sequences,the divergence time tree of marine chironomids Chironomidae was constructed.A total of 39 species of marine chironomids were identified,belonging to 19 genera of 3 subfamilies,including 4 species of 2 genera of Telmatogetoninae,13 species of 8genera of Orthocladiinae and 22 species of 9 genera of Chironominae.Based on the phylogenetic tree,the following conclusions are drawn: in the tribe Chironomini,the results showed that Zhouomyia and Ainuyusurika were sister groups to each other,and then formed sister groups with Polypedilum;Hanochironomus belongs to Chironomus complex;In the tribe Tanytarsini,Yaetanytarsus and Pontomyia are sister groups,and the first two genera and Tanytarsus are sister groups.The phylogenetic relationships of other subfamilies are basically consistent with previous studies.Based on the divergence time tree of marine chironomids,four different types of marine origin were proposed,but different types varied from group to group.Among them,Zhouomyia and Ainuyusurika are sister groups,which is a secondary atavistic evolution group from fresh water invasion to sea water invasion;Yaetanytarsus and Pontomyia are sister group,This group is a relict group of ancient marine species with abundant biodiversity and primitive characters;Clunio and Thalassosmittia are an independent group of marine chironomids,whose related genera marine chironomids live in dry coastal environment;Telmatogetoninae is a primitive marine species,which can be regarded as original marine habitants.Some species of Telmatogetoninae have invaded and will continue to invade into freshwater habitats with less competitive pressure.