Recently Evolved, Stage-Specific Genes Are Enriched at Life-Stage Transitions in Flies.

Understanding how genomic information is selectively utilized across different life stages is essential for deciphering the developmental and evolutionary strategies of metazoans. In holometabolous insects, the dynamic expression of genes enables distinct functional adaptations at embryonic, larval, pupal, and adult stages, likely contributing to their evolutionary success. While Drosophila melanogaster (D. melanogaster) has been extensively studied, less is known about the evolutionary dynamics that could govern stage-specific gene expression. To address this question, we compared the distribution of stage-specific genes, that is, genes expressed in temporally restricted developmental stages, across the development of D. melanogaster and Aedes aegypti (A. aegypti). Using tau-scoring, a computational method to determine gene expression specificity, we found that, on average, a large proportion of genes (20%-30% of all protein-coding genes) in both species exhibit restricted expression to specific developmental stages. Phylostratigraphy analysis, a method to date the age of genes, further revealed that stage-specific genes fall into two major categories: highly conserved and recently evolved. Notably, many of the recently evolved and stage-specific genes identified in A. aegypti and D. melanogaster are restricted to Diptera order (20%-35% of all stage-specific genes), highlighting ongoing evolutionary processes that continue to shape life-stage transitions. Overall, our findings underscore the complex interplay between gene evolutionary age, expression specificity, and morphological transformations in development. These results suggest that the attraction of genes to critical life-stage transitions is an ongoing process that may not be constant across evolutionary time or uniform between different lineages, offering new insights into the adaptability and diversification of dipteran genomes.