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Whilst the Arctic and boreal bumblebee fauna is increasingly studied worldwide, information is missing about the genetic connections between circum-boreal populations of some widespread species, especially those living in remote regions like North-East Siberia and Alaska. Here, we study one of the most common boreal bumblebee species, Bombus (Pyrobombus) jonellus (Kirby, 1802), as a model to investigate current circum-boreal genetic connections and relations with relictual populations in its post-glacial refugia in Southern Europe. Our haplotype network analysis based on a fragment of the cytochrome oxidase 1 gene reveals two main conspecific lineages, one in Europe including the Southern relictual populations from the Pyrenees and the second comprising Eastern Palearctic and Nearctic populations. However, West-Siberian populations of Bombus jonellus share haplotypes with the two distinct lineages. These results could indicate a postglacial, multidirectional and circum-boreal recolonization both in Europe and East-Palearctic from refugia in Siberia, in addition to other recolonization ways from Southern European refugia and Beringia. These findings highlight that a priori distant and isolated conspecific populations of B. jonellus could presently remain connected or have only presented a recent break in gene flow.

Bombus glacialis Friese, 1902 is an Arctic bumblebee that was thought to have a disjunctive range on the Arctic Ocean Islands, i.e., on Novaya Zemlya and Wrangel Island, with a 3600 km gap between these isolates. While the species status of the Novaya Zemlya’s population was recently confirmed using a molecular approach, its close affinities to the Wrangel’s isolate were proposed by a morphological similarity alone. Here, we report that B. glacialis samples from Wrangel share three unique COI haplotypes, which are closely related to each other and to those inferred from samples from Novaya Zemlya. Based on a combination of diagnostic morphological and molecular characters, the Wrangel’s population is described here as a new subspecies, Bombus glacialis marinae ssp. nov. Our novel data indicate that this species can be considered a polar relict that had had a much broader distribution along the continental margin of Eurasia during the Pleistocene. The two subspecies of B. glacialis were likely separated in the Middle Pleistocene (mean age = 0.27 Myr, 95% CI = 0.12–0.46 Myr) due to increasing of the sea level during an interglacial. The Novaya Zemlya Archipelago supported a B. glacialis population in the Late Pleistocene. Hence, this insular land was not covered completely by ice sheet during the Last Glacial Maximum. Our findings highlight that relict cold-adapted Pleistocene lineages still survive on remote islands in the Arctic Ocean and that such lineages are highly threatened by recent climate warming.

The evolutionary biogeography of the Arctic Ocean islands is a relatively little-known topic. The Novaya Zemlya Archipelago, a severe mountain land of glaciers, rocks, Arctic deserts and tundra, is among the most enigmatic places in the world because it was a closed area for more than half a century. Here, we report the results of an integrative study of Bombus glacialis Friese, 1902, which has been described from the archipelago. We found that this island lineage has a high level of mtDNA COI gene divergence and a unique nucleotide substitution in the nDNA EF-1α gene but is a sister taxon of B. lapponicus and B. sylvicola. A redescription of the species using Friese’s syntype and newly collected topotypes from Novaya Zemlya is presented. Our results confirm the species status of B. glacialis from Novaya Zemlya, although its relationships with morphologically similar lineages inhabiting other High Arctic areas (Kolguev Island, Kanin Peninsula and Wrangel Island) should be determined in the future. Overall, new findings highlight that the Arctic Ocean archipelagos could preserve cold-tolerant Quaternary relict lineages of invertebrates, which currently may be on the brink of extinction due to climate warming.