Characterizing the Genome of the Bumblebee Bombus haematurus – A Range-Expanding Pollinator

Over the past two decades, the blood-tailed bumblebee Bombus haematurus has expanded its range from Western Asia into Central Europe. It is among several members of the Pyrobombus subgenus of bumblebees to have undergone recent population expansions. A number of studies have investigated these other species for genomic signatures that might be associated with expansions. Currently there are no published studies describing whole genome resources for B. haematurus and no whole genome data from regions near the edge of the expanding front. Here, we sequenced samples of B. haematurus from part of its recently expanded range in Northern Italy to generate the first whole genome data for this species. The genome size of B. haematurus is in a similar range to that reported for closely related Pyrobombus species (∼300 mega base pairs), with a predicted ∼ 13,500 genes. At the location sampled, there was a comparatively low nucleotide diversity, low inbreeding evidenced through a negative inbreeding coefficient, F _IS (-0.14), and low percentage of genome covered by long runs of homozygosity, LROH (∼0.03%), compatible with a recent history of population expansion. Using nucleotide diversity and Tajima’s D, we also detected evidence of positive and balancing selection in developmental biology and signalling genes. Comparison with other members of the Bombus genus and Pyrobombus subgenus revealed similar biological processes to be associated with signatures of selection across the genus. Our comparison also identified similar trends of F _IS and LROH between B. haematurus and other Pyrobombus species.