The influence of social environment on cooperation and conflict in an incipiently social bee, Ceratina calcarata

Abstract

How mutual tolerance is produced, and the role of social environment in inducing cooperation in social groups, remains unstudied in many simple societies. In particular, maternal and sibling care and conflict are challenging to manipulate experimentally for many species. Most bees are solitary, but mothers of the eastern small carpenter bee, Ceratina calcarata, engage in prolonged care of offspring, and are therefore subsocial. Females form social associations of parents and a single generation of offspring, including a smaller dwarf eldest daughter (DED) who forages and feeds her adult siblings. Adult assemblages of C. calcarata present a unique opportunity to study the effect of social environment on cooperation and sibling care in an otherwise subsocial bee. To study how social environment influences foraging and intranidal behaviors, observation nests were constructed, and unaltered as a control, or treated by removing either only mothers or both mothers and DEDs. Nests were video-recorded for 464 h during summer (July–August) parent-adult offspring cohabitation. Individual and interactive behaviors were scored. In the absence of mothers, offspring were more tolerant, suggesting that a hierarchy between mother and offspring produces less tolerance between offspring. Aggression was only significantly greater in the absence of both mother and DED. We found that foraging was the lowest in the absence of mothers, and persisted in the absence of both mother and DED. This study provides the first detailed account of the intranidal behaviors of this species and experimentally reveals how social environment influences cooperative behavior. Understanding how particular life histories, such as extended parental care, may set the stage for more complex social behaviors, such as sibling cooperation, is critical to understanding how alloparental care evolves in group living organisms. Most species exhibiting parental care and sibling cooperation are difficult to manipulate experimentally. Though relatively uncommon in invertebrates, extended parental care is frequently found in small carpenter bees that can be carefully observed within their nests and foraging. Here, we examine how the absence of mothers and worker-like daughters influences the social behavior of related adults living in close group association of such bees. This experiment presents an intranidal study of a subsocial bee’s behavior, and our results suggest that mothers play a dramatic role regulating social behavior. Furthermore, our results show that siblings are more tolerant in the absence of mothers, suggesting that mothers may maintain social hierarchies among offspring. Siblings may interact more aggressively and more frequently as they negotiate intranidal and foraging tasks in the absence of maternal care.