Loss of the queen activates the dopaminergic pathway in worker bees.

The loss of the queen induces neuroendocrine changes in worker bees. Apis mellifera and promotes ovarian activation. Research has identified a progressive increase in dopamine in the brain, alterations in receptors in the ovary, and greater activity of hormonal pathways associated with reproduction. Results indicate integration between neural and endocrine signaling during the onset of egg laying by worker bees.

The study evaluated worker bees kept in colonies with and without queens. Researchers collected individuals after 14 days and classified them into three ovarian stages: inactive, partially active, and fully active. Samples allowed for the quantification of brain dopamine and analysis of gene expression related to the synthesis, transport, and metabolism of this neurotransmitter, as well as genes linked to juvenile hormones and the 20-hydroxyecdysone pathway.

Elevated dopamine

Results indicated an increase in cerebral dopamine during the progression of ovarian development. Worker bees with fully active ovaries showed levels 1,50 times higher compared to the intermediate stage and 1,11 times higher compared to the initial stage. No difference was observed between worker bees with inactive ovaries in colonies with or without a queen.

Molecular analyses showed increased expression of genes involved in the production and regulation of dopamine in the brain. These include tyrosine hydroxylase (Amth), dopa decarboxylase (Amddc), dopamine transporter (Amdat), and arylalkylamine N-acetyltransferase (Amnat). These genes showed higher expression in worker bees with active ovaries.

Dopamine receptors exhibited a distinct pattern between the brain and the ovary. In the brain, there was no relevant variation between ovarian stages. In the ovary, there was a reorganization in sensitivity to the neurotransmitter. The Amdop1 receptor showed an increase during ovarian activation. The Amdop3 receptor showed a reduction with the advancement of the reproductive process.

Hormonal pathways

Research also detected increased activity in hormonal pathways linked to reproduction. Genes associated with the juvenile hormone, such as JHAMT, MFE, Met, and Kr-h1, showed higher expression in worker bees with active ovaries. Markers of the 20-hydroxyecdysone pathway—Neverland, Shadow, EcR, and E75—also increased as ovarian development progressed.

Some hormonal genes showed elevation even in worker bees without active ovaries within queenless colonies. The pattern suggests early endocrine preparation after the queen's absence. This process may precede the morphological changes observed in the ovary.

The set of results indicates dopaminergic remodeling associated with the reproductive activation of worker bees. Changes in neural and hormonal signaling form an integrated network linked to ovarian development in the absence of the queen.

Further information at doi.org/10.3390/insects17030308