Phylogeny of the bee genus Lasioglossum (Hymenoptera: Halictidae) based on mitochondrial COI sequence data

The bee genus Lasioglossum Curtis is a model taxon for studying the evolutionary origins of and reversals in eusociality. This paper presents a phylogenetic analysis of Lasioglossum species and subgenera based on a data set consisting of 1240 bp of the mitochondrial cytochrome oxidase I (COI) gene for seventy-seven taxa (sixty-six ingroup and eleven outgroup taxa). Maximum parsimony was used to analyse the data set (using paup *4.0) by a variety of weighting methods, including equal weights, a priori weighting and a posteriori weighting. All methods yielded roughly congruent results. Michener’s Hemihalictus series was found to be monophyletic in all analyses but one, while his Lasioglossum series formed a basal, paraphyletic assemblage in all analyses but one. Chilalictus was consistently found to be a basal taxon of Lasioglossum sensu lato and Lasioglossum sensu stricto was found to be monophyletic. Within the Hemihalictus series, major lineages included Dialictus + Paralictus, the acarinate Evylaeus + Hemihalictus + Sudila and the carinate Evylaeus + Sphecodogastra. Relationships within the Hemihalictus series were highly stable to altered weighting schemes, while relationships among the basal subgenera in the Lasioglossum series (Lasioglossum s.s., Chilalictus, Parasphecodes and Ctenonomia) were unclear. The social parasite of Dialictus, Paralictus, is consistently and unambiguously placed well within Dialictus, thus rendering Dialictus paraphyletic. The implications of this for understanding the origins of social parasitism are discussed.