Abstract
Simple SummaryIn this review, we describe sex-specific differences in the regulatory systems for dopamine production in the brains of social insects, focusing on the honey bee. Dopamine has a crucial role in the promotion of reproduction in both sexes of the honey bee and is a key substance for understanding the mechanisms underlying the reproductive division of labor in females. Studies associated with dopamine regulation have been performed mainly in females, with less of a focus on its regulation in males. In social insects, males are specialized for reproduction and do not exhibit division of labor; however, they have evolved to adapt their social system and have acquired/discarded physiological and behavioral characteristics. Therefore, studies exploring the dopaminergic system in males can contribute to our understanding of social adaptation in males. We integrate findings related to dopamine in both honey bee sexes and provide insights into the physiology involved in dopaminergic systems in social insects.Dopamine has multiple functions in the modulation of social behavior and promotion of reproduction in eusocial Hymenoptera. In the honey bee, there are sex-specific differences in the regulation of dopamine production in the brain. These different dopaminergic systems might contribute to the maintenance of sex-specific behaviors and physiology. However, it is still not fully understood how the dopaminergic system in the brain is regulated by endocrinal factors and social stimuli in the colony. In this review, we focus on the regulation of dopamine production in queens, workers, and males in the honey bee. Dopamine production can be controlled by queen substance, juvenile hormone, and exogenous tyrosine from food. Queens can control dopamine production in workers via queen substance, whereas workers can manipulate the supply of tyrosine, a precursor of dopamine, to queens and males. The regulation of dopamine production through social interaction might affect the reproductive states of colony members and maintain sex-specific behaviors in unpredictable environments.
Highlights
Introduction iationsThe division of labor in eusocial insects is fundamental to the organization of insect societies
The effects of dopamine production by queen mandibular pheromone (QMP) are unknown, but such details are required for a complete picture of sex-specific dopamine production in the honey bee
These findings led to the ‘brain amine manipulation hypothesis’, whereby the brain levels of dopamine and other biogenic amines synthesized from tyrosine in males can be manipulated by workers
Summary
Caste differences in the brain levels of dopamine have been reported in adult honey bees [29,30]. Emerged queens have higher expression levels of genes encoding tyrosine hydroxylase (Amth) and DOPA decarboxylase (Amddc) compared with newly emerged workers [30]. Queens are fed ‘royal jelly’ by nurse bees; this contains the dopamine precursor, tyrosine [32,33,34] They are fed royal jelly during the late larval stages and when they are adults, whereas adult workers feed on honey and pollen [2]. It has been reported that female larvae fed larger amounts of royal jelly become adult females with higher levels of dopamine, tyrosine, and DOPA in the brain [31]. The differences in the dopamine levels are smaller in the bumble bee (approximately two-fold) than in the honey bee (approx. four-fold)
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