Evolutionary dynamics of insect odorant receptors reveal ecological tuning shaping olfactory perception

Insect olfaction is facilitated by a heterotetrameric odorant receptor–odorant receptor co-receptor (OR-Orco) complex, which is distinct from that of vertebrate ORs. However, extreme sequence divergence among insect ORs has hindered a unified understanding of their evolutionary history and ecological importance. In this study, we present a multiscale analysis of OR genes across 115 insect species. We overcome the limitations of traditional phylogenetic approaches by applying a protein similarity network-based strategy and introduce a "trunk–branch" framework to systematically describe the evolutionary trajectories of insect ORs across sequence, structural, and predicted olfactory potential levels. Although they possess different sequences and structural communities, all sampled insect orders contained ORs assigned to all six docking-derived functional communities. Notably, extant insect lineages with order-level origins spanning the end-Permian mass extinction (EPME) differed in docking-derived functional OR repertoires, and early-and late-diverging lineages differed in OR sequence-community diversity. The emergence of Orco represents a key evolutionary transition point, marking the shift from a homomeric to a heteromeric complex accompanied by specialization of the extracellular domain and binding pocket. Furthermore, we established robust associations between potential olfactory recognition breadth and ecological variables, including diet, circadian rhythm, and habitat. Our findings provide a class-level framework for investigating insect OR evolution and generate testable hypotheses about how receptor repertoire diversification may relate to ecological adaptation.