Phylogenomics, biogeography, and host-plant evolution in Callandrena (Hymenoptera: Andrenidae), a group of specialist bees on Asteraceae

Callandrena is a subgenus within the genus Andrena (Hymenoptera: Andrenidae), comprising 86 species. It is recognized as the largest entirely Nearctic subgenus, ranging from southern Canada to Panama and across the United States. All Callandrena species are specialists on Asteraceae, utilizing plants from five different tribes. Despite their interesting biology as host-plant specialists, understanding of the group’s evolutionary history is hindered by taxonomic and phylogenetic uncertainty within Andrena. Recent evidence suggests that the subgenus is non-monophyletic and that specialization on Asteraceae evolved several times, convergently. To better understand host-plant transitions and diversification in the subgenus, we aimed to create a comprehensive phylogeny of Callandrena species using new and publicly available phylogenomic data. Using the phylogeny, we estimated divergence times and explored the timing of Asteraceae specialization in Andrena. Within Callandrena we further explored host-plant transitions to different tribes of Asteraceae and correlations with diversification and biogeography.