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MBE Advance Access published online on April 20, 2005
Molecular Biology and Evolution, doi:10.1093/molbev/msi148
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© The Author 2005. Published by Oxford University Press on behalf of the Society for Molecular Biology and Evolution. All rights reserved. For permissions, please e-mail: journals.permissions@oupjournals.org
Accepted April 7, 2005

Research Article

The Phylogenetic Positions of Three Basal Hexapod Groups (Protura, Diplura & Collembola) Based on Ribosomal RNA Gene Sequences

Yunxia Luan 1*, Jon M. Mallatt 2, Rongdong Xie 1, Yiming Yang 1, and Wenying Yin 1

1 Institute of Plant Physiology & Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200032, China
2 School of Biological Sciences, Washington State University, Pullman, WA 99164-4236, USA

* To whom correspondence should be addressed.
Yunxia Luan, E-mail: yxluan{at}sibs.ac.cn


  Abstract

This study combined complete 18S with partial 28S rRNA gene sequences (~2000 nt total) to investigate the relations of basal hexapods. Ten species of Protura, 12 of Diplura, and 10 of Collembola (representing all subgroups of these three clades) were sequenced, along with five true insects and eight other arthropods, which served as outgroups. Trees were constructed with maximum parsimony, maximum likelihood, Bayesian analysis, and minimum-evolution analysis of LogDet-transformed distances. All methods yielded strong support for a clade of Protura plus Diplura, here named Nonoculata, and for monophyly of the Diplura. Parametric-bootstrapping analysis showed our data to be inconsistent with previous hypotheses (P <0.01) that joined Protura with Collembola (Ellipura), that said Diplura are sister to true insects or are diphyletic, and that said Collembola are not hexapods. That is, our data are consistent with hexapod monophyly, and Collembola grouped weakly with ‘Protura+Diplura’ under most analytical conditions. As a caveat to the above conclusions, the sequences showed nonstationarity of nucleotide frequencies across taxa, so the CG-rich sequences of the diplurans and proturans may have grouped together artifactually; however, the fact that the LogDet method supported this group lessens this possibility. Within the basal-hexapod groups, where nucleotide frequencies were stationary, traditional taxonomic subgroups generally were recovered: i.e., within Protura the Eosentomata and Acerentomata (but Sinentomata was not monophyletic); within Collembola the Arthropleona, Poduromorpha and Entomobryomorpha (but Symphypleona was polyphyletic); and in Diplura the most complete data set (>2100 nt) showed monophyly of Campodeoidea and of Japygoidea, and most methods united Projapygoidea with Japygoidea.

Keywords: Protura; Diplura; Collembola; Ribosomal RNA Genes; Molecular Phylogeny.
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