Behavioural plasticity in the fanning response of bumblebee workers: impact of experience and rate of temperature change

Keywords: behavioural plasticity Bombus terrestris bumblebee division of labour experience response threshold model self-organization self-reinforcement thermoregulation Flexible division of labour is a key feature of social insects. Our understanding of individual response behaviour and how it is integrated into a functioning colony is still patchy. Most theoretical studies addressing this question are based on the assumption that workers have intrinsic and often fixed response thresholds for task related stimuli. Here, we investigated the plasticity in worker fanning response behaviour in a bumblebee, Bombus terrestris. Using a temperature controlled brood dummy, we first asked whether the fanning response is modulated by rate of temperature change. Second, we examined to what extent the fanning response is influenced by recent fanning experience. Our results show that the individual fanning response is modulated by both the rate of temperature increase and recent experience. Workers responded at lower temperatures and with a higher probability when the temperature of the brood dummy increased slowly compared with more rapid temperature increases. Workers that repeatedly responded to an increase in brood dummy temperature with fanning showed a significant decrease in their response thresholds, whereas the response thresholds of control workers that experienced the same treatment but did not gather fanning experience remained unchanged. The decrease in response threshold was pronounced when the time interval between two successive fanning events was less than 6 h. When 16 h or more separated fanning events, individual fanning responses returned to higher threshold levels. We suggest that experience dependent modulation of response thresholds plays an important role in the behavioural differentiation of workers and the flexibility of insect colonies. Division of labour is a key property of insect societies. Workers perform different subsets of all tasks necessary for colony func tioning and are allocated to those tasks without any central control. It is commonly assumed that division of labour among the workers of a colony is the primary reason for the unsurpassed ecological success of social insects (Oster & Wilson 1978; Hölldobler & Wilson 1990). One of the most remarkable features of division of labour is that colonies display an amazing degree of plasticity and resiliency. They respond to external changes and internal demands by adjusting the ratios of workers allocated to the various tasks; and they are able to compensate quickly for the removal of a substantial proportion of their workforce by rapid reallocation of workers from Our understanding of the …