Discovery of a Nearctic vicariant bumblebee (Hymenoptera: Apidae) in Eurasia uncovers secondary trans-Beringian exchanges of insect faunas

Repeated emergence and disappearance of the Bering Land Bridge during the Quaternary triggered multiple faunal exchanges between northeast Asia and North America. Older (Early to Middle Pleistocene) dispersal events through the bridge followed by its submergence often lead to the vicariant origin of sister species, whose allopatric ranges are currently separated by the Bering Strait. Among bumblebees, examples of these pairs include Bombus balteatus Dahlbom 1832 – B. kirbiellus Curtis 1835, B. pyrrhopygus Friese 1902 – B. polaris Curtis 1835, and B. hyperboreus Schönherr 1809 – B. natvigi Richards 1931. However, integrative taxonomic analyses of new bumblebee samples from hard-to-reach areas of the Chukotka Peninsula (Russian Far East) reveal that the Nearctic B. kirbiellus is present at the north-eastern margin of Asia and that its Asian specimens share the COI haplotype with populations from Alaska. Although B. kirbiellus originated as a Nearctic relative of B. balteatus and was thought to be an endemic to North America, there was a Late Pleistocene (or more recent) expansion of this species from Alaska to Chukotka. Our findings indicate the possibility of secondary expansion of vicariant species through the Beringia during the Last Glacial Maximum or via a more recent migration event across the Bering Strait.