Análise da morfologia e do transcriptoma dos ovários no desenvolvimento de operárias da abelha sem ferrão Melipona quadrifasciata

Abstract

Eusocial bees exhibit a division of labor between queens and workers, in which the queen is primarily responsible for colony reproduction. However, in some species, workers retain the ability to produce viable haploid eggs and contribute to colony offspring, as observed in Melipona quadrifasciata. This characteristic raises questions about the molecular mechanisms and transcriptional programs that allow workers to reach adulthood with developed and functional ovaries. In this context, the present study aimed to characterize the ovaries of M. quadrifasciata workers throughout the pupal stage by integrating morphological and transcriptomic analyses. Ovaries were examined using cellular labeling and fluorescence microscopy, while the transcriptome was investigated through RNA sequencing (RNA-seq), employing differential gene expression and gene co-expression analyses to identify genes and modules associated with ovarian development. Morphological characterization revealed that the basic ovarian structures are already established during the early pupal stages, including the organization into four ovarioles, the presence of a terminal filament, and a germarium region containing polyfusomes and ring canals. Developmental progression was marked by major structural changes beginning with the onset of body pigmentation, when the vitellarium became distinguishable and contained developing oocytes associated with nurse cell chambers. Differential expression analyses corroborated this pattern, indicating that the final developmental stage exhibited the highest number of differentially expressed genes, including genes related to ecdysteroid biosynthesis, juvenile hormone pathways, and reproductive processes. Co-expression analyses revealed modules characterized by a progressive decrease in expression throughout development, with hub genes potentially involved in gene repression, chromatin remodeling, ubiquitination, and ecdysteroid biosynthesis. In contrast, a module displaying an antagonistic expression profile showed peak expression at the final developmental stage and contained genes associated with hormonal response, cell signaling, and tissue maturation. Together, these results indicate that ovary development during pupal stage in M. quadrifasciata is characterized by coordinated transcriptional reorganization associated with metamorphic hormone dynamics and the sequential activation of distinct genetic programs. This study expands current knowledge of ovarian development in stingless bees and provides evidence for the integrated involvement of hormonal, epigenetic, and cell signaling mechanisms in the formation of fertile ovaries in worker bees.