Reproductive aggression and nestmate recognition in a subsocial bee

Abstract

In social contexts, the ability to recognize and discriminate among individuals is advantageous, because it allows individuals to adjust their behaviour so as to enhance both individual and group fitness. Eusocial insects have finely developed mechanisms of discrimination that promote many kinds of social interactions, but discrimination may also be adaptive in noneusocial species, including solitary ones. Physical traits such as reproductive status influence rates of aggression and discrimination, permitting individuals to share common resources and nesting sites and to cooperatively care for offspring, while excluding potential aggressors or social parasites. In this study, we examined reproductive aggression and nestmate recognition in a subsocial species of small carpenter bee, Ceratina calcarata, using circle tube behavioural assays. Not only does this subsocial bee show nestmate recognition, but there is seasonal variation in aggression that correlates with seasonal variation in reproductive status, illustrating that both aggressive behaviour and the consequences of nestmate recognition are context dependent. Females that were actively reproductive (ovaries fully developed) were more aggressive than pre-reproductive (ovaries undeveloped) or post-reproductive females (ovaries resorbed). Females altered their behaviour when interacting with nestmates versus non-nestmates. As in most social Hymenoptera, agonistic behaviour was observed to be greatest between unfamiliar, reproductively active individuals. However, post-reproductive females were tolerant towards unfamiliar females. During the natural adult cohabitation phase of the nesting cycle (the mature brood phase), mothers were aggressive towards daughters, whereas same generation pairs of nestmates or non-nestmates showed no signs of aggression. These results indicate that this subsocial bee species does possess the ability to recognize nestmates but the consequences of recognition vary seasonally, sometimes resulting in greater aggression towards nestmates than towards non-nestmates.