Abstract
Most bees collect pollen and nectar for their larvae, while some also collect other resources. We investigated the evolution of floral oil-collecting behaviour in the Apidae and the evolutionary effects of floral oils on host brood cells for cuckoo bees.
Focusing on apid bee phylogeny, we reconstructed the evolution of floral oil collection by females, use of floral oils in cell construction and the inclusion of oils in provisioning immatures. Ancestral character reconstruction demonstrates that floral oil-collecting behaviour arose four times independently.
We also found that in cuckoo bees, parasitization of oil-collecting bees arose three times (including one secondary return) in Apidae. Except for Ctenoplectrina, oil cuckoo bees are all closely related to each other, forming an independent clade within the Nomadinae.
Analysis of evolutionary transition rates indicates that there is a greater tendency for switching from an oil-collecting host to a non-oil-collecting host than the reverse. In apid bees, evolutionary transition rates are higher for switching to cuckoo behaviour from an ancestral lineage in which females collect floral oils than from other pollen-collecting lineages.
We conclude that adaptation to oil collection is advantageous for pollen-collecting bees, and that the origin of oil cuckoo bees from non-oil cuckoo bees is constrained.