Queen–worker aggression in the facultatively eusocial bee Megalopta genalis

Abstract

The establishment of reproductive division of labor in primitively eusocial insects is typically based on dominance interactions from the queen toward her worker daughters. We used a standardized behavioral assay, the circle tube, to observe aggressive and other behaviors between the queen and workers of field-collected social colonies of the sweat bee, Megalopta genalis. Queens generally expressed higher levels of aggressive and dominant behaviors than workers. Workers performed two behaviors, ‘C-posture’ and ‘reverse’, more frequently than queens. Our data suggest a defensive function for C-posture in workers, as it correlated with the expression of queen aggression. Within queens, the aggressive behaviors ‘nudge’, ‘bite’, ‘push’, and ‘chase’ correlated with each other in their frequencies of expression; the other two behaviors that were performed more often by queens (‘back up’ and ‘back into’) did not. The two behaviors performed more often by workers, ‘C-posture’ and ‘reverse’, were not correlated in workers. Queen and worker activity levels were correlated. Body size correlated with increased expression of queen-like behavior in both the queen and worker castes. Queens generally were bigger and had larger ovaries than workers. Queen–worker body size and ovary size differences correlated with behavioral differences. The effects of body size suggest an influence of developmental nutrition on adult behavior.