Age, Caste, and Social Context Shape Ovarian Morphology and Transcriptomic Profiles in Red Harvester Ants (Pogonomyrmex barbatus)

Reproductive division of labor defines eusocial insects like ants, where queens reproduce and workers remain mostly sterile. Yet, some workers retain rudimentary ovaries, raising questions about their reproductive potential. We examined morphological and transcriptomic differences in ovaries of Pogonomyrmex barbatus queens and workers of varying ages and social contexts. Queens had large, yolk-rich oocytes, while worker ovaries showed signs of degeneration. Callow workers had more developed ovaries than mature ones, suggesting reproductive decline with age. Queenless workers showed more ovarian regression compared to queenright ones. Transcriptomic analyses revealed over 2,000 differentially expressed genes between castes, including those involved in metabolism, hormonal signaling, and epigenetic regulation. Notably, queenless workers upregulated a fertility-linked gene and downregulated lipid metabolism genes. Our results show that both age and social environment constrain worker reproductive potential, highlighting the queen’s role in maintaining worker sterility and offering insights into reproductive senescence in eusocial systems.