Acknowledgements
The authors acknowledge Steve Bogdanowicz, the Cornell Evolutionary Genetics Core Facility, the Cornell Lab of Ornithology, Bronwyn Butcher, and the Lovette Lab for help in method development and for providing lab space and time. Dave Moeller and Indrani Singh helped with bee identification and provided helpful natural history knowledge, and Amy Hastings helped in DNA extraction methods. We thank Julia Brokaw, who was instrumental in the field collections of bees and pollen, as well as Alyssa Anderson, who aided in data preparation. This work was supported by the National Science Foundation Doctoral Dissertation Improvement Grant program, grant number 1701675 awarded to ARMJ and MAG, and NSF DEB-1754299 awarded to MAG.