Abstract
Colony sociobiology in social Hymenoptera is shaped by multiple factors including the queen, colony size, worker demography, and other environmental and genetic factors. The production of sexuals, particularly of gynes, often marks the climax of colony development and the ultimate purpose for building the worker force. However, the mechanisms regulating this process are largely unknown in most species.
Here we examined the role of the brood in regulating sexual production and shaping colony development using colonies of the social bumble bee Bombus impatiens. In this species, the impact of the queen on worker reproduction and aggression is stronger when combined with the brood, and young larvae are able to reduce egg-laying in workers. However, these studies were conducted using small female groups, and how the brood regulates colony-level events, such as the onset of worker reproduction and gyne production, remained unexplored. To address this, we examined the development of young colonies containing double amount of brood (db), no brood (nb), and unmanipulated control colonies for 26 days. We show that following brood manipulation, db colonies produced significantly more gynes whereas nb colonies produced significantly more males. Additionally, we found that worker reproduction started sooner in nb colonies and was delayed in db colonies, while aggression overall was the highest in the db colonies. Overall, our findings indicate that the brood effect is not limited to small groups and has significant implications on colony development and sociobiology. The mechanisms determining female castes in social species are still mostly unknown and brood may be a key to understanding how demographical changes throughout the colony development shape social behavior and may also explain the variation in reproductive strategies across bumble bee colonies and other social species.
Competing Interest Statement
The authors have declared no competing interest.