Queen Loss Remodels Brain Dopamine and Hormonal Pathways During Worker Ovary Activation in Apis mellifera

In honey bees, reproductive division of labor is maintained by social suppression of worker fertility, yet queen loss can trigger ovary activation in workers. Here, we tested whether endogenous dopaminergic signaling is progressively remodeled across successive stages of ovarian activation and how these changes relate to key hormone pathways. Newly emerged Apis mellifera workers were introduced into queenright or queenless colonies, collected after 14 days, and classified as having inactive, partially activated, or fully activated ovaries. We quantified brain dopamine and measured expression levels of genes involved in dopamine synthesis, transport, metabolism, and reception in both brain and ovary tissues, together with transcriptional markers of juvenile hormone (JH) and 20-hydroxyecdysone (20E) signaling. Brain dopamine increased with ovary activation and peaked in fully activated workers, coincident with elevated transcripts of tyrosine hydroxylase, dopa decarboxylase, dopamine transporter, and arylalkylamine N-acetyltransferase in the brain. Dopamine receptor genes were stable in the brain but were remodeled in the ovary, with Amdop1 increasing and Amdop3 decreasing during activation. Markers of JH signaling and ovarian 20E pathway activity also rose with ovarian development, consistent with early endocrine priming following queen loss. Collectively, these results support an integrated neuroendocrine framework in which dopaminergic remodeling and hormone pathway activation jointly accompany worker reproductive activation under queenless conditions.