Molecular phylogeny of the bumble bee subgenus Pyrobombus (Hymenoptera:Apidae:Bombus) with insights into gene utility for lower-level analysis

Abstract

Comprising nearly 20% of all bumble bees, the subgenus Pyrobombus is distributed across diverse habitats in the Northern Hemisphere and exhibits considerable morphological and behavioural variation relative to other subgenera. Its size and variation have led to questions concerning its monophyly and intrasubgeneric relationships, but too few known morphological synapomorphies and insufficient taxon sampling have precluded robust answers to these questions. To obtain a robust phylogeny of the group, we obtained DNA sequences for 36 of the 43 species from four genes (mitochondrial 16S rRNA and three nuclear genes: elongation factor – 1α (EF-1α), long wavelength rhodopsin (LW Rh or opsin) and arginine kinase (ArgK)). Both Bayesian and parsimony phylogenies are well resolved and indicate a monophyletic Pyrobombus when assessed against representatives of 20 additional subgenera. The more conserved nuclear genes, especially EF-1α and ArgK, provided good support across all of the taxonomic levels examined, whereas support of the more rapidly evolving mt16S was restricted mostly to close relationships at the tips of the tree. The exon regions of ArgK were the most conserved and may be promising for higher-level phylogenetics. We discuss species relationships within Pyrobombus and its sister-group, Bombus s.s. + Alpinobombus, in relation to previous taxonomic studies.