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

## TL;DR

When the queen bee is lost, worker bees activate their ovaries, and this process involves changes in brain dopamine and hormone pathways.

## Contribution

This study reveals how dopamine and hormone signaling change in worker bees as they activate their ovaries after queen loss.

## Key findings

- Brain dopamine levels increase as worker ovaries become more active.
- Dopamine receptor genes in the ovary shift during activation, suggesting reorganized sensitivity.
- Juvenile hormone and 20-hydroxyecdysone signaling also increase with ovarian development.

## Abstract

In honey bee colonies, a single queen usually produces most of the eggs, while worker bees typically do not reproduce. When the queen is lost, some workers can activate their ovaries and begin laying eggs, helping the colony persist. However, the biological signals that connect queen loss to worker reproduction are not fully understood. We studied worker bees from colonies with and without a queen and compared individuals at three stages of ovary development, from inactive to fully active. We found that workers with fully active ovaries had higher levels of dopamine, a chemical messenger in the brain. At the same time, key genes that support dopamine production and movement in the brain increased. In the ovary, two dopamine receptors shifted in opposite directions as ovaries became active, suggesting that the ovary’s sensitivity to dopamine is reorganized during reproduction. We also observed increased activity of two major insect hormone systems that regulate reproduction. Together, these results show how brain signaling, ovarian sensitivity, and hormone-related changes may work together to enable worker reproduction after queen loss.

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.