Molecular phylogeny of the major arthropod groups indicates polyphyly of Crustaceans and a new hypothesis for the origin of Hexapods

Abstract

A phylogeny of the arthropods was inferred from analyses of amino acid sequences derived from the nuclear genes encoding elongation factor-1α and the largest subunit of RNA polymerase II using maximum-parsimony, neighbor- joining, and maximum-likelihood methods. Analyses of elongation factor-1α from 17 arthropods and 4 outgroup taxa recovered many arthropod clades supported by previous morphological studies, including Diplopoda, Myriapoda, Insecta, Hexapoda, Branchiopoda (Crustacea), Araneae, Tetrapulmonata, Arachnida, Chelicerata, and Malacostraca (Crustacea). However, counter to previous studies, elongation factor-1α placed Malacostraca as sister group to the other arthropods. Branchiopod crustaceans were found to be more closely related to hexapods and myriapods than to malacostracan crustaceans. Sequences for RNA polymerase II were obtained from 11 arthropod taxa and were analyzed separately and in combination with elongation factor-1α. Results from these analyses were concordant with those derived from elongation factor-1α alone and provided support for a Hexapoda/Branchiopoda clade, thus arguing against the monophyly of the traditionally defined Atelocerata (Hexapoda + Myriapoda).