Evolutionary Analysis of Sex-Biased Gene Suggests Functional Conservation of Lifespan-Related Genes in Insecta

Sex-biased gene expression is a fundamental driver of sexual dimorphism and plays an important role in evolutionary divergence across species. Here, we conducted a comparative evolutionary analysis of sex-biased genes (SBGs) in 13 insect species spanning four major orders: Hemiptera, Diptera, Lepidoptera, and Coleoptera. In total, 42,488 SBGs were identified, with low interspecific conservation—86.5% of orthogroups were shared by six or fewer species. Phylogenetic analyses showed that SBGs generally follow evolutionary trajectories similar to other protein-coding genes but show branch length differences suggestive of accelerated evolution in Drosophila virilis and Tribolium castaneum. Male-biased genes were more conserved than female-biased genes, which often showed reversed expression patterns, particularly in T. castaneum. Functional annotation of three rapidly evolving orthogroups in T. castaneum indicates possible associations with sex-specific traits such as lifespan, muscle development, and immunity, which should be considered hypotheses for future functional validation. These findings highlight the complex evolutionary dynamics of sex-biased genes and their contributions to phenotypic diversity and adaptive evolution in insects, providing a basis for future studies on the molecular mechanisms of sexual dimorphism and lineage-specific adaptations.