Abstract
Physiological state profoundly influences the expression of the behaviour of individuals and can affect social interactions between animals. How physiological state influences food sharing and social behaviour in social insects is poorly understood. Here, we examined the social interactions and food sharing behaviour of honeybees with the aim of developing the honeybee as a model for understanding how an individual's state influences its social interactions. The state of individual honeybees was manipulated by either starving donor bees or feeding them sucrose or low doses of ethanol to examine how a change in hunger or inebriation state affected the social behaviours exhibited by two closely-related nestmates. Using a lab-based assay for measuring individual motor behaviour and social behaviour, we found that behaviours such as antennation, willingness to engage in trophallaxis, and mandible opening were affected by both hunger and ethanol intoxication. Inebriated bees were more likely to exhibit mandible opening, which may represent a form of aggression, than bees fed sucrose alone. However, intoxicated bees were as willing to engage in trophallaxis as the sucrose-fed bees. The effects of ethanol on social behaviors were dose-dependent, with higher doses of ethanol producing larger effects on behaviour. Hungry donor bees, on the other hand, were more likely to engage in begging for food and less likely to antennate and to display mandible opening. We also found that when nestmates received food from donors previously fed ethanol, they began to display evidence of inebriation, indicating that ethanol can be retained in the crop for several hours and that it can be transferred between honeybee nestmates during trophallaxis.
Highlights
Homeostatic mechanisms for the maintenance of physiological state regulate many important behavioural processes in animals including foraging for and consuming food
On the other hand, inebriated bees, and in particular the 10% ethanol-fed bees, were more likely to repeatedly open and close their mandibles without performing trophallaxis (1-way ANOVA, F3,142 = 2.82, P = 0.041)
The second function accounted for 35.5% of the variation and significantly separated the donor bees fed 1.0 M sucrose from the hungry, unfed bees (CDA, x242 = 40.9, P = 0.017; Table 1). This function was largely represented by data from factors 3 and 4 in the PCA (Table S1); F3 was characterized by the fact that bees that exhibited mandible opening were less likely to beg for food whereas F4 predominantly represented a correlation between trophallaxis and upside down behaviour
Summary
Homeostatic mechanisms for the maintenance of physiological state regulate many important behavioural processes in animals including foraging for and consuming food. In social insect societies such as bee or ant colonies, food seeking behaviour is largely carried out by specialist foragers who continually forage such that they collect food and return to share it with other colony members. Adult bees feed directly from colony stores of pollen or honey, foraging worker honeybees use a portion of the food they collect or they are often given food from nestmates (e.g. nurses) rather than eating honey reserves (reviewed in Crailsheim, 1998) [5]. Food sharing is an important way that nestmates communicate their own hunger state to other nestmates to aid in the regulation of foraging within the colony [7,10]. Whether or not hunger state influences the dynamic of food sharing beyond an increase in food solicitation is not wellunderstood
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