Phylogeny and biogeography of the cleptoparasitic bee genus Nomada revisited

The cleptoparasitic bee genus Nomada (Hymenoptera: Apidae) is the most diverse lineage of cleptoparasitic bees and is found on every continent except Antarctica. We used molecular data to validate 13 of the original 16 species groups found in Nomada and uncovered a formerly unknown group. We also estimated divergence dates using fossil calibration points and inferred the origin and diversification of this genus around the globe. Our phylogeny provided support for 14 of the 16 previously established species groups, with two groups needing to be unified into a single group and another found to be paraphyletic. All remaining species groups were found to be monophyletic. Historical biogeographic reconstruction indicates that Nomada originated in the Holarctic ~65 Mya. Geodispersal into the southern hemisphere occurred three times; once during the Eocene into the Afrotropics, once during the Oligocene into the Neotropics, and once during the Miocene into Australasia. Geodispersal across the Holarctic was most frequent and occurred repeatedly throughout the Cenozoic era, using the De Geer, Thulean, and the Bering Land Bridges. This is the first instance of a bee using both the Thulean and De Geer land bridges and has implications of how early bee species dispersed throughout the Palearctic in the late Cretaceous and early Paleogene.