The Diversity Of Symbiodinium In Scleractinian Corals In The Coastal Waters Surrounding Hainan Island

The special symbiosis between scleractinian corals and intracellular,photosynthetic dinoflagellates of the genus Symbiodinium usually regulates the nutrition,development and changes of coral reef ecosystem.Investigating the taxonomy and diversity of Symbiodinium is important in understanding how coral reefs will respond to envioronmental changes.We investigated the composition of the dinoflagellate genus Symbiodinium in the coastal waters surrounding Hainan island,by polymerase chain reaction of large subunit rRNA and restriction fragment length polymorphism(PCR-RFLP),sequencing of polymerase chain reaction amplified fragments of ITS rRNA(including direct and clone sequencing)and next-generation sequencing of the ITS2 maker gene.The mainly results as followed:1)The results of PCR-RFLP(with Rsal)of large subunit rRNA showed that Symbiodinium clade C and D were the dominant in scleractinian corals in the coastal waters surrounding Hainan island.In Wenchang and Wanning(on the eastern coast of Hainan)and Danzhou and Changjiang(on the western coast of Hainan),clade C was the dominant.but clade C and D were the mainly clades in Sanya located in the south of Hainan.2)Sequencing(including direct and clone sequencing)of ITS rRNA genes showed that the clade C were clustered with two previous studied groups Symbiodinium subclade(type)C1 and C15,and the clade D was consisted of subclade D1a.The Symbiodinium subclades of Wenchang and Changjiang(east coast)were C1,Wanning and Danzhou(west coast)were C1 and C15.However,in Sanya(south coast),the subclades C1,C15 or D1a were domainant in the scleractinian corals.3)The high-throughput sequencing of the ITS2 marker to assess Symbiodinium community composition and diversity showed that the clade C,presented highest diversity,and included 27 types of C1,C21 and C15 subclades and so on.The diversity of clade D was low,only containing D17,D1,D2 and D2.2 the four types.While,clade G contained only G3 subclade with the lowest diversity.The composition of Symbiodinium diversity were mainly with C1,C21,C15 and D17 subclades,which occupying a proportion up to 95%.According to the geographical region,C1,C21 and C3.14 were the primarily subclades in Wenchang.In Danzhou were C1,C21 and C15 subclades.However,in Sanya were C1,C21 and D17 subclades.4)This study suggested that most scleractinian hosts were not specific in forming coral-symbiosim symbionts on the levels of coral species/genera,such as Montipora truncates hosted the subclades Cl/C21 of Symbiodinium in Wenchang and Danzhou,however,which hosted the subclade C15 in Sanya.The mainiy subclades of Symbiodinium in the host-coral of the same species or genera usually were coincident in the same region,but which significantly vary in different species or genera of hosts.Furthermore,The corals of the same species or genera usually host similar domainant subclades in the eastern and western coast of Hainan,and which host different types of Symbiodinium in south Sanya.Therefore,for the majority of host genera or species,the composition of the dominant Symbiodinium was largely corresponded to the geographical environment factors of the hosts.5)The diversity distribution of symbiodinium in scleractinian corals in the coastal waters surrounding Hainan island had certain regional characteristics.In the eastern and western of Hainan,the diversities of Symbiodinium were both consistent and uneven geographically.Even if in similar latitude,the composition of primarily Symbiodinium types were also different,such as the Symbiodinium types of C1,C21 and C3.14 in Wenchang(eastern coast of Hainan),but C1,C21 and C15 in Danzhou(western coast of Hainan).Moreover,the Symbiodinium were gradually transformed from clade C clade to C and D clades.Moreover,the diversities of Symbiodinium increased gradually with the temperature increasing from the north to the south of Hainan island.This geographic distribution fully reflected the adaptability and plasticity of Symbiodinium to the diverse ecological environment.The multicopy marker showed a high level of resolution at the species level.6)PCR-RFLP method showed a high level to resolution at the clades level.Direct/cloning sequencing method in most cases was to measure the highest abundance type of the Symbiodinium.While,high-throughput sequencing method not only fully presented the Symbiodinium diversity of high abundance types,but also detected the low abundance types.Besides,the results of direct/cloning sequencing were basically consistent with the highest abundance Symbiodinium types of high-throughput sequencing,but there were still some differences.For instance,the results of direct/cloning sequencing were C1 subclades in M.truncate in Wenchang,whereas the results of high-throughput sequencing were C21 subclades;For Acropora rosaria,in Sanya,the results of direct/cloning sequencing were D1a subclades,the results of high-throughput sequencing were D17 subclades.There were 3 mainly reasons for this discrepancy:the first was that the ITS maker gene with larger quantities of information than ITS2;the Second was that the blast clustal databases used in the two methods of sequencing results were different.The third was that the two sequencing methods had different primer-preferences.