Functional conservation and diversification in the Lepidoptera ionotropic receptor IR75q.2 lineage

In insects, antennal ionotropic receptors (IRs) play a crucial role in the detection of airborne chemicals. However, little functional information is available beyond drosophilids, particularly in terms of their functional evolution. In the present study, we functionally assayed IR75q.2 orthologues from eight moth species and found that three of them primarily responded to nonanoic acid, with secondary responses to octanoic acid, while the others showed no response to any of the tested acids. Further, molecular docking showed that the key amino acids directly interacting with the ligand are conserved across different species, indicating that the functional divergence among IR75q.2 orthologues is driven by amino acid substitutions that do not directly interact with target compounds but may alter the shape of the binding pocket or overall protein configuration. Evolutionary analysis revealed that subfunctionalization following gene duplication contributed to the specialization of IR75q.2 in Lepidoptera. These findings highlight the evolutionary plasticity of chemosensory receptors and advance our understanding of the molecular basis of olfactory adaptation in moths.