Phylogenetic And Morphological Evolution Of Green Euglenophytes

In this paper,based on the sequences of 16 S rRNA,18 S rRNA and 23 S rRNA gene,the means of morphology,taxonomy,molecular biology and bioinformatics were used to build phylogenetic trees of green euglenophytes by Neighbor-joining method,Maximum Parsimony method and Bayesian method and reconstruct their ancestor on the base of 8 morphological characters by Bayesian tree.It will be helpful in clearing phylogenetic relationships among green euglenophytes and providing theoretical basis for researching their origin.The results are as follows:(1)Phylogenetic relationships among green euglenophytes: Phacus and Lepocinclis are sister groups and the support rate is high in phylogenetic trees except for the NJ tree based on 18 S rRNA sequences.Eutreptia and Eutreptiella gather to the same clade in all phylogenetic trees and have high support rate,indicating that they are close relatives.As both Trachelomonas and Strombomonas have lorica,they tend to form a single clade in phylogenetic trees and have high support rate.Euglena,Euglenaria,Cryptoglena,Monomorphina and Colacium usually gather together,so they have close relatives.Discoplastic mostly gathers in a clade with the genus Phacus and gets high support rate,indicating that they are closely related.All phylogenetic trees show that Euglena is not a monophyletic group.(2)The results of ancestor reconstruction based on 8 morphological characters by 16 S rRNA,18 S rRNA and 23 S rRNA sequences were almost identical,and they showed that ancestor reconstructions of green euglenophytes were the same which were based on six characters: degree of surface hardening,superficial stripe,shape of posterior end,lorica and flagellar pore,shape of chloroplast,shape and quantity of paramylon grains.Corresponding 6 relatively original states included cuticula soft and easy deformation,spirally striated,posterior end slightly narrowing or sharp elongated cauda,without lorica,chloroplasts show sheet,shield,or plate,with many small grains are primitive traits.The two characters length of flagella and pyrenoid of chloroplast can not infer possible ancestral states because of states frequency close to each other or showing none certain states.(3)The results of ancestral reconstruction based on 8 morphological characters by three genes showed that Euglena and Euglenaria which have original characters may be the ancestor of green euglenophytes who appear earliest.