Evolution of the α-Glucosidase Gene Family in Apoidea.

With more than 20,000 recognized species, the Apoidea is one of the most significant groups of pollinating insects, and their living environment is complex and diverse. The composition of nectar-producing plants for Apoidea varies across different geographical regions, prompting this group to evolve a variety of adaptive traits at the morphological and physiological levels to enhance their survival. The adaptive evolution of digestive enzymes is crucial for efficient nutrient absorption in Apoidea; however, the molecular basis underlying the diversification of bee digestive enzymes remains unclear. This study analyzed 63 α-glucosidase sequences from the GH13 family, representing the three subfamilies Hbg1, Hbg2, and Hbg3, across six families within Apoidea. Phylogenetic analysis indicates that the α-glucosidase gene family underwent two divergence events during the early evolution of the Apoidea superfamily, giving rise to the GH13 family members Hbg1, Hbg2, and Hbg3; compared to the ancestral lineage, these three members exhibit significant divergence in both expression patterns and enzymatic functions. The GH13 genes in honeybees exhibit substantial structural diversity. Furthermore, clear functional divergence was observed among the subfamilies, accompanied by signatures of positive selection in specific lineages and codon sites. Twenty-eight sites near the ligand-binding region of α-glucosidase are subject to positive selection and functional divergence, which may be related to the ligand-binding and hydrolytic properties of α-glucosidase. Overall, the α-glucosidase gene family has undergone adaptive evolution driven by positive selection in Apoidea, leading to the expansion and diversification of this gene family.