Abstract
Odorant-binding proteins (OBPs) and chemosensory proteins (CSPs) serve as carriers for signal molecules within the insect olfactory system, playing a crucial role in detecting chemical cues related to feeding and reproduction. However, their roles in host shift and environmental adaptation remain poorly understood. This study identified the OBP and CSP gene families across 32 Drosophila species, revealing their adaptive evolutionary trajectory. It was found that the gene number of the OBP family varied widely between species, ranging from 37 to 66 genes, while the gene number of the CSP family was conserved. The OBP family experienced two major gene expansion events on the ancestral branches of the diet-diverse melanogaster lineage, leading to an increased number. Positive selection occurred during evolution in the orthologous groups of Obp22a, Obp57e and Obp83ef. Homology modeling and molecular docking revealed that variation in the positively selected sites across different Drosophila species resulted in significant changes to free binding energy and affinity for plant odors and insecticides. Our findings highlight gene expansion and functional diversification within the Drosophila OBP family may contribute to shaping the dietary spectrum and promoting adaptation to toxic substances.
