The Phylogenetic Analyses Of Entomobryidae, Entomobryoidea And Collembola

Collembolans are small arthropods with furcula. So it is also called springtail. And it is the most abundant group of the basal Arthropoda as well as Diplura and Protura. Six hundred and eighty six genera and over 8000 species belong to this class have been reported from all over the world. The morphology of Collembola has been widely studied. However, the controversies about the taxonomy and the phylogeny of it are existent. In this study, some reviews which focus on the history of the study and some important morphologic characters (chaetotaxy and body scales, etc.) were made to give a brief introduction. And we also discussed both the mitochondrion and mitochondrial genome of Collembola. After that, we provided the phylogenetic analysis of this class.This study provided the description of the complete mitochondrial genome of two species of Collembola. And we showed the methods of sampling, amplification, sequencing and annotation to assemble the two complete mitochondrial genomes. After that, we took phylogenetic analyses based on both nucleotide and amino acid sequences of the 13 PCGs by the means of MrBayes. The topology of the phylogenetic trees showed a normal relationship about the major groups among Collembola, but at some specific nodes, the results challenged the traditional taxonomy by morphology. In this phylogenetic analysis, Arthropleona and Entomobryomorpha are paraphyletic and the observed phylogenetic grouping [Onychiuridae+(Poduridae+(Hypogastruridae+ Neanuridae))], obtained in both nucleotide tree and amino acid tree is in strong disagreement with the morphological analyses taken by other researchers who prefer the relationship like [Onychiuridae+ (Hypogastruridae+(Poduridae+Neanuridae))]. Discrepancies between different analyses may be resolved with a denser taxon sampling for both Hypogastruridae and Neanuridae.In this study, a molecular phylogeny was also reconstructed using the nuclear 18S rRNA and partial 28S rRNA and the mitochondrial 16S rRNA to examine relationship across Entomobryidae subfamilies. These datasets were analyzed with parsimony, likelihood and Bayesian algorithms. Monophyly of Orchesellinae was not recovered, and it was split into a scaled clade and an unscaled clade, contradicting to all recent taxonomic conceptions. The monophyly of most groups is well supported with some other groups are not (within Entomobryinae, the monophyly of Entomobryini was not recovered as well as Willowsiini of Orchesellinae) which implies that classification using the presence/absence of scales is not valid. Analyses of ancestral character state reconstruction in Entomobryidae were taken to provide some detail about the evolution of body scales. The result of this analyses indicate that the presence of body scales have evolved independently at least five times, with a loss of scales occurring independently at least twice. A revision of the family Entomobryidae on molecular and morphological basis is clearly needed. At the same time, the phylogeny of Entomobryoidea was reconstructed here based on mitochondrial and ribosomal fragments. The trees as well as topology tests, which use the likelihood and Bayesian approaches both rejected the traditional hypotheses relying on furcula morphology. Further ancestral character reconstructions were carried out and phylogenetic signals of tergal, specialized chaetae (S-chaetae) together with some other important morphological characters were examined. And furcula together with body scales were turned to be multiple independent origins in Entomobryoidea whereas tergal, specialized chaetae (S-chaetae) exhibited strong phylogenetic signals.