Barcoding cryptic bumblebee taxa: B. lucorum, B. crytarum and B. magnus, a case study (Hymenoptera: Apidae: Bombus).

Abstract

Spring queens of five taxa of the subgenus Bombus sensu stricto (Bombus sporadicus, B. terrestris, B. lucorum, B. cryptarum and B. magnus) were collected from different localities throughout Europe to rear artificial colonies. The mitochondrial cytochrome oxidase subunit I of 40 specimens was sequenced (partial sequence of 1005 bp length). Interspecific sequence divergence was about 30 to 60 base substitutions and the Tamura-Nei genetic distance was approximately 0.05 to 0.25, whereas the intraspecific sequence divergence was only 1 to 6 base substitutions and the Tamura-Nei genetic distance was about 0.002 to 0.007. In addition to the B. sporadicus and B. terrestris cluster, three clusters were obtained in the phylogenetic tree: cluster α for B. lucorum, cluster β for B. cryptarum and cluster γ for B. magnus. The three clusters α, β and γ, which represent taxa of the so-called lucorum-complex, were well separated, with low variability, no intergrading and no terminal units of unclear position. As there are no gaps in the alignments of the cytochrome oxidase subunit I sequences single nucleotide sites can be used as positional homologies. Each taxon is characterised by about 8 to 12 substitutions, which are unique (“private”) and can be used as diagnostic characters to define and identify that taxon. Using the classical tools of cladistics, a tree was built on the basis of these diagnostic characters. The Barcode engine successfully identified all critical specimens. The topological position of GenBank sequences of misidentified specimens and sequences with potentially degraded DNA is discussed. Museum specimens of three Asiatic taxa of the lucorum-complex with unknown relationships were sequenced to investigate the possibility of identifying specimens with degraded DNA by diagnostic positions. Identification based on morphological and molecular characters is discussed and the identification of critical specimens by tree building (= genetic distance) and by diagnostic characters is compared.