Phylogenomic and morphological reevaluation of the bee tribes Biastini, Neolarrini, and Townsendiellini (Hymenoptera: Apidae) with description of three new species of Schwarzia

Authors: BOSSERT, SILAS - Cornell University; COPELAND, ROBERT - Smithsonian Institute; SLESS, TREVOR - Cornell University; BRADY, SEAN - Smithsonian Institute; DANFORTH, BRYAN - Cornell University; Branstetter, Michael; GILLUNG, JESSICA - McGill University - Canada; STRAKA, JAKUB - Charles University, Czech Republic

Submitted to: Insect Systematics and Diversity
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/24/2020
Publication Date: 11/12/2020
Citation: Bossert, S., Copeland, R.S., Sless, T.J., Brady, S.G., Danforth, B.D., Branstetter, M.G., Gillung, J., Straka, J. 2020. Phylogenomic and morphological reevaluation of the bee tribes Biastini, Neolarrini, and Townsendiellini (Hymenoptera: Apidae) with description of three new species of Schwarzia. Insect Systematics and Diversity. 4(6). https://doi.org/10.1093/isd/ixaa013.
DOI: https://doi.org/10.1093/isd/ixaa013

Interpretive Summary: Bees include over 20,000 species and are vital to pollination in natural and agricultural environments. Due to their immense diversity, the task of discovering and describing all bee species remains far from complete. In a new study led by researchers from Cornell University, the diversity of a small group of enigmatic bees that parasitize other bee species was investigated. We report the discovery of three new bee species from eastern Africa and estimate the evolutionary relationships among these species and several closely related bee groups using genomic data. Based on the evolutionary results, this research makes significant improvements to bee nomenclature and provide novel insights into the age and geographic origin of the studied bees. Overall this work improves foundational knowledge of global bee diversity and provides new resources for identifying and communicating about bees.

Technical Abstract: Bees of the tribes Biastini, Neolarrini, and Townsendiellini are cleptoparasites in nests of solitary bees. Understanding their phylogenetic relationships has proven difficult for many decades. Previous research yielded ambiguous results because of conflicting phylogenetic signals of larval and adult morphological characters. Molecular data settled some of this disparity but our knowledge remains fragmented due to limited taxon sampling and the discovery of a new lineage associated with Biastini: the enigmatic Schwarzia. Schwarzia has unusual morphological features and seems transitional between previously established taxa. This puts limits on our ability to diagnose the groups, understand their antiquity and biogeography, and study the evolution of host-choice in a comparative framework. To address this, we integrate phylogenomics and morphology to establish a fossil-calibrated phylogeny for the tribes Biastini, Neolarrini, and Townsendiellini. We show that Schwarzia is indeed closely related to Biastes, but Biastes itself is paraphyletic in respect to Neopasites, and even Biastini is paraphyletic due to Townsendiella, which is sister to Rhopalolemma. To ensure monophyly, we lower Neopasites to subgeneric rank within Biastes and resurrect Melittoxena as a third subgenus. We then assess the diagnosability of different tribal concepts and establish an expanded tribe Neolarrini that includes Biastini and Townsendiellini. Neolarrini in the new, expanded sense likely originated in the Nearctic in the mid-Eocene and is, as far we know, composed exclusively of parasites of oligolectic hosts. Lastly, our continued efforts to find the rare Schwarzia in Eastern Africa led to the discovery of three new species, which are extensively treated herein.