Study On Complete Mitochondrial Genome Of Cypridopsis Vidua And Molecular Phylogeny Of Ostracoda

Ostracod is one group of Crustacea (Arthropoda) and is aquatic animal with small size. It play an important role in ecology, geology, paleobiology and evolutionary biology, and were called as "the model species which have great potential in evolutionary biology". However, its roles in above mentioned field has been limited because of a poor reseach on ostracods. The aim of this study is to reveal the evolutionary relationships and provide molecular evidences for further study of Ostracoda.1. The complete mitochondrial genome of Cypridopsis vidua and the phylogenetic analysis of OstracodaThe mitochondrial genome of C. vidua was 16,783 bp which contains 13 PCGs, two rRNAs,22 tRNAs and one non-coding region. The genome of C. vidua have an overall A+T content of 73.75%(A=36.72%, C=15.74%, G=10.51%, T=37.03%). The AT and GC skews for the mitochondrial genome of C. vidua were-0.004 and-0.199, respectively, illustrating the occurrence of more T than A, and C than G. All the 13 PCGs used the conventional start codon (ATG, ATA and ATT). The coding regions of the COI, COII, ATP6, ATP8, ND3, ND6, CYTB, ND4L and ND2 genes were terminated by TAA, while COIII and ND5 were TAG. Two incomplete stop codons (T--) were found on the ND1 and ND4 gene ends.Comparing the gene arrangements of C. vidua with other two ostracods (Fabaeformiscandona kushiroensis and Vargula hilgendorfii) and the typical arthropod gene arrangement, it was clear that the gene order and orientation of F. kushiroensis was the most similar to that of the typical arthropod, followed by C. vidua and V. hilgendorfii. This interesting transform could give us useful information about the molecular evolution of ostracods, e.g., the evolutionary trajectory of C. vidua was more complex than that of F. kushiroensis in the subclass Podocopa, while this podocopan species might be more conservative than myodocopan (V. hilgendorfii) in evolution. To detect phylogenetic position of C. vidua, the mitochondrial genome amino acid sequences of individual PCGs of C. vidua and other 58 "Pancrustacea" were selected from GenBank to be used in the study. The Maximum Parsimony (MP) tree was constructed by PAUP 4.0. The phylogenetic tree in this study showed that hexapods had a close relationship with crustaceans and these two groups could not be separated from each other. This result supported the view of "Pancrustacea". Although! C. vidua and F. kushiroensis belong to two different family (Cyprididae and Candonidae, respectively) in the subclass Podocopa, our MP phylogenetic tree showed a close phylogenetic relationship between C. vidua and F. kushiroensis with the bootstrap value of 100%, indicating that cypridid and candonid ostracods might originate from a common ancestral ostracod.2. Molecular phylogeny of Ostracoda inferred from 18S ribosomal DNAWe sequenced the 18S ribosomal DNA of five ostracods (Heterocypris salina, Cypretta turgida, Cypria kraepelini, Limnocythere inopinata and Darwinula stevensoni) and 140 sequences of other ostracods and "Pancmstacea" were obtained from NCBI to construct the phylogenetic trees. The results showed that (1) the traditional classification of Myodocopa was supported, in which Cladocopina and Halocypridinae belong to Halocyprida and the Myodocopida contains Cypridinoidea, Sarsielloidea and Cylindroleberididae; (2) podocopa is a monophyletic group, and the Cytherellidae was moved to Podocopida from Platycopida, while Platycopida contains Punciidae only and the phylogenetic relationships of ((((Bairdiocopina+ Darwinulocopina)+Cytherellocopina)+Cypridocopina)+Cytherocopina) were formed within Podocopida. Meanwhile, the relationships of three superfamily within Cypridocopina is ((Macrocypridoidea+Pontocypridoidea)+Cypridocopina).