Changes in biogenic amine levels and physiological traits of the reproductive caste during caste-specific life events in temperate paper wasps

Abstract

In temperate paper wasps, members of the reproductive caste undergo drastic environmental and behavioral changes throughout their life history. In this study, we aimed to clarify the changes in the biogenic amine levels and physiological traits in the reproductive caste in the periods of emergence, mating, during and after overwintering, nest founding, and colony establishment (i.e., becoming the colony queen). In addition, we analyzed the relationships between biogenic amines in the brain and ovarian development or lipid stores in the abdomen during each life event for reproductive females. The amounts of lipids were highest in females during the mating period and gradually decreased until becoming the colony queen. Brain levels of dopamine increased toward the nest-founding period and correlated with egg maturation in the ovary, indicating that dopaminergic reproductive control may have played a key role in the reproductive caste. Changes in the brain levels of tyramine coincided with changes in day length as tyramine levels decreased when the day-length was short. In addition, tyramine was associated with ovarian development in reproductive castes, as also found in reproductive workers, suggesting it may have played a role in gonadotropic functioning through day length information. Thus, we characterized the physiological changes in response to caste-specific events in the reproductive castes of temperate paper wasps.