The Phylogeny Of Basal Hexapods Based On Ribosomal RNA Gene Sequences

Controversies about the phylogenetic relationships of basal hexapods have keptgrowing in recent years, with the monophyly of Diplura and the phylogenetic positionsof Protura, Diplura, and Collembola being the hot spots of dispute. These questions arecritical for understanding the early steps of the evolution of Insecta and the phylogenyof Arthropoda. The complete 18S rDNA (~2000bp) and partial 28S rDNA (~400bp) sequences of10 proturan species (from Acerentomata, Eosentomata, and Sinentomata), 11 dipluranspecies (from Campodeoidea, Japygoidea and Projapygoidea), and 8 collembolanspecies (from Arthropleona and Symphypleona) were analyzed in this study.Combining related sequences of insects (species from aptergotan silverfish,palaeopteran mayfly, and neopteran locust) and other arthropods (species fromCrustacea, Myriapoda, and Chelicerata), the phylogenetic trees were obtained by usingMP (Maximum Parsimony), ML (Maximum Likelihood), and BI (Bayesian Inference)methods. The results indicated that: I. The monophyly of Diplura, Protura, Collembola, and Insecta s.str. was well supported, respectively; II. The phylogenetic analyses of proturan species confirmed the monophyly of Acerentomata and Eosentomata. Sinentomidae and Fujientomidae were independent groups in Protura; III中科院博士论文 通过核糖体 RNA 基因序列分析探讨低等六足动物的系统发生 III. Projapygoidea occupied an intermediate position between Campodeoidea and Japygoidea in the phylogenetic trees and was closer to Japygoidea than to Campodeoidea. To our knowledge, this is the first report that analyzed DNA sequence from the third group in Diplura. IV. In the phylogenetic trees of collembolan species, Poduromorpha [(Poduridae + Neanuridae) + Onychiuridae + Hypogastruridae] was monophyletic; Podura aquatica consisted of a sister group of Neanuridae and nested within Arthropleona. Symphypleona was paraphyletic; V. Diplura had a close phylogenetic relationship to Protura instead of to Insecta s.str.. The monophyly of Ellipura (=Parainsecta, Protura+Collembola) gained no support in our analyses; VI. Our results suggested that Hexapoda was not monophyletic and the basal hexapods might be in parallel with Insecta s.str.. On the other hand, our results provided evidence for a Crustacea + Hexapoda clade (Pancrustacea), thus arguing against the monophyly of the traditionally defined Atelocerata (Myriapoda + Hexapoda).