The aberrant millipede genus Pteridoiulus and its position in a revised molecular phylogeny of the family Julidae (Diplopoda : Julida)

Abstract

A phylogenetic analysis of 62 species (32 genera) of the Palaearctic millipede family Julidae, including the aberrant alpine genus Pteridoiulus Verhoeff, 1913, was made based on partial sequences of the mitochondrial 16S rRNA (16S) gene and the nuclear 28S rRNA (28S) gene, respectively. The two datasets (16S rDNA and 28S rDNA) were analysed in combination but treated as different partitions using direct optimisation as implemented in POY. The 16S rDNA and the 28S rDNA sequences vary from 410 to 449 bp and from 467 to 525 bp in length, respectively. All searches were performed under six different gap opening costs, an extension gap cost of 1, and a substitution cost of 2. Based on previous investigations the optimal gap opening cost was set to 4, and the robustness of different gap opening costs ranging from 1 to 6 investigated. Additionally, the two data partitions were aligned individually using MAFTT and run in TNT both with gaps treated as a fifth state, and as missing, and finally the alignments were used as input in a maximum likelihood (ML) analysis. The order Julida and the family Julidae were recovered as monophyletic under all weight sets in POY, as well as in the TNT and ML analyses. Likewise, in all analyses Pteridoiulus was found to be sister to another monotypic alpine genus, Heteroiulus Verhoeff, 1897. The Pteridoiulus + Heteroiulus clade is robust to parameter changes but lacks morphological support. The distribution pattern of the clade, Pteridoiulus in the eastern Alps (mainly Austria), Heteroiulus in the southern Alps (Italy) seems unique, since similar patterns all involve very similar, closely related species pairs.