Behavioral and genomic divergence between a generalist and a specialist fly

The evolution of feeding habits leads to speciation in insects. Bactrocera true fruit flies display diverse feeding habits across species. We combine behavioral and functional genomic studies to probe the divergence between the specialist B. minax and the generalist B. dorsalis. We find that both vision and olfaction contribute to their respective host preferences, with a dominant effect of vision over the olfaction in short range. Correspondingly, host location-related genes are significantly enriched in the phototransduction pathway, of which the long-wavelength rhodopsin confers the color preference in both species and has been subject to selection in the specialist. We also find a massive expansion of olfactory receptors in the generalist, along with signatures of conditional expression and positive selection. The phylogenetic context suggests an ancestrally important role of vision in the host location of Bactrocera, as well as the increased performance and plasticity of olfaction alongside the arising of generalism.