Chemosensory evolution across populations of a specialised bee pollinator are associated with shifts from wild to agricultural plants

Crop domestication exerts powerful selective forces on both the cultivated species and the ecological networks within which it is embedded. Selection on human-beneficial traits during domestication can also alter other traits due to epistasis and complex gene-environment interactions that lead to domesticated plants having unique sets of phenotypes compared to wild plants. Here, we investigate olfactory system evolution across populations of a specialist bee, Eucera pruinosa, that restricts pollen collection to the plant genus Cucurbita that comprises a large number of domesticated species (pumpkins, squashes, gourds). E. pruinosa has experienced a recent range shift from xeric environments to mesic areas where they encounter only domesticated plants. We show that this transition from wild and agricultural environments is associated with the expansion of olfactory genes and signatures of adaptive selection on odorant receptors. This study demonstrates the ways in which crop domestication can rapidly alter the evolutionary trajectories of species dependent on crop plants.