Phylogeny, taxonomics, and ovipositor length variation of the Pteromalus albipennis species group (Hymenoptera: Chalcidoidea: Pteromalidae: Pteromalinae)

The Pteromalus albipennis species group currently comprises 29 Palaearctic parasitoid wasp species associated with tephritid fly larvae developing in flower heads of Asteraceae. The species group is taxonomically challenging, because its putative species are morphologically extremely similar to each other except for some conspicuous differences in gaster length, which is a reliable proxy for the ovipositor length. Ovipositor length dictates the accessibility of host larvae to the parasitoid female and thus largely determines the host range of a species. In this study, we infer the phylogenetic relationships of currently recognized species of the P. albipennis species group by analyzing the nucleotide sequences of 124 protein-coding genes spanning more than 310,000 bp. The data were analyzed by applying the maximum likelihood optimality criterion (concatenated sequence data) as well as a multispecies coalescent approach (analyzing gene trees). Based on the inferred species trees, we (a) re-evaluate previous species hypotheses in comparison with the new phylogenomic results and (b) assess whether or not ovipositor length variation is phylogenetically constrained. Our results show some incongruence between morphology-based and phylogenomics-based species delimitations and suggest the existence of paraphyletic species. Furthermore, our study suggests that ovipositor length is no reliable predictor of phylogenetic relatedness, but a labile trait, possibly reflecting rapid evolution of host range differences. Taxonomic ambiguities and the scarce knowledge on the biology of the analyzed species highlight the difficulties of studying parasitoid wasps, even in the Western Palaearctic, and despite the application of integrative taxonomics approaches (i.e., the use of hundreds of genes for taxonomy).