Evolutionary Novelty of Apolipoprotein D Facilitates Metabolic Plasticity in Lepidopteran Wings.

Understanding metabolic plasticity of animal evolution is a fundamental challenge in evolutionary biology. Owing to the diversification of insect wing morphology and dynamic energy requirements, the molecular adaptation mechanisms underlying the metabolic pathways in wing evolution remain largely unknown. This study reveals the pivotal role of the duplicated Apolipoprotein D (ApoD) gene in lipid and energy homeostasis in the lepidopteran wing. ApoD underwent significant expansion in insects, with gene duplication and consistent retention observed in Lepidoptera. Notably, duplicated ApoD2 was highly expressed in lepidopteran wings and encoded a unique C-terminal tail, conferring distinct ligand-binding properties. Using Bombyx mori as a model organism, we integrated evolutionary analysis, multiomics, and in vivo functional experiments to elucidate the way duplicated ApoD2 mediates lipid trafficking and homeostasis via the AMP-activated protein kinase pathway in wings. Moreover, we revealed the specific expression and functional divergence of duplicated ApoD as a key mechanism regulating lipid homeostasis in the lepidopteran wing. These findings highlight an evolutionary scenario in which neofunctionalization conferred a novel role of ApoD in shaping adaptive lipid metabolic regulatory networks during wing phenotypic evolution. Overall, we provide in vivo evidence for the functional differentiation of duplicate genes in shaping adaptive metabolic regulatory networks during phenotypic evolution.