Abstract
Complete metamorphosis of holometabolous insects is a complex biological process characterized by profound morphological, physiological, and transcriptional changes. To reveal the temporal dynamics of gene expression during this critical developmental transition, we conducted a detailed analysis of the developmental transcriptomes of two Drosophila species, Drosophila melanogaster and Drosophila virilis. We confirmed partial recapitulation of the embryonic transcriptional program in pupae, but unlike the traditional hourglass model, suggesting maximal conservation at mid-embryonic stages, at different stages of pupae we observed a more complicated pattern of alternating low and high diversity, resembling an inverted hourglass, or "spindle". This underscores the complexity of developmental processes during complete metamorphosis. Notably, recently formed genes (specific to insects) exhibit pronounced expression peaks during mid-pupal development, indicating their potential role in developmental transitions.