Social interactions and their connection to aggression and ovarian development in orphaned worker bumblebees (Bombus impatiens)

This study examines the social dynamics of reproductive conflict. Orphaned worker bumblebees (Bombus impatiens) with comparatively high or low levels of social activity were paired to determine whether aggression and reproduction could be traced to earlier social interactions. The workers were paired according to their levels of social activity (a socially active + another socially active worker, socially active + socially inactive, and two socially inactive workers). The presence or absence of brood was also manipulated. The absence of brood increased both aggression and ovarian development, suggesting that aggression and reproduction are associated or that there is a third variable that affects both. Socially active pairs were significantly more aggressive: here, social activity can be taken as an early indicator of aggression. No such effect, however, was obtained on ovarian development as the socially active pairs did not differ on their degree of ovarian development compared to the others. Within the socially active + socially inactive pairs, the socially active worker did not have more developed ovaries and was not more aggressive than her socially inactive partner. Results highlight that environmental conditions (the absence of brood) can predict ovarian development and although social activity can be observed prior to aggression, differences in aggression do not translate into differences in ovarian development under these conditions.