Ovarian regulation of foraging division of labour in Africanized backcross and pollen-hoarding honeybees

Division of labour (i.e. differential task performance) is the hallmark of social insects. One highly studied component of honeybee division of labour is foraging specialization through collection of protein (pollen) or carbohydrates (nectar). The reproductive ground plan hypothesis proposes that this foraging division of labour is regulated by the same physiological control networks that controlled foraging behaviour during the reproductive life cycle of solitary honeybee ancestors. Based on observed differences in foraging behaviour and reproductive anatomy between bees selected for storing high and low quantities of pollen (high and low pollen-hoarding strains) and observed differences between wild-type pollen and nectar foragers, the reproductive ground plan hypothesis suggests that ovary size in facultatively sterile worker honeybees has a regulatory effect on variation in foraging division of labour, with increased protein bias correlated with increased ovary size (measured as ovariole number). An alternative explanation for the link between ovary size and foraging behaviour is that genes for ovarian development and foraging are inherited together because of genetic linkage or chance gene associations in the selected and natural populations. To address this alternative explanation, we investigated the relationship between ovary size and foraging bias in honeybees where genetic linkage was broken using a backcross mating design. We also studied high- and low-strain bees where ovary size effects were partitioned from other potential linkage effects. We found that ovariole number was related to foraging bias in the backcross bees and in the selected strains, as predicted by the reproductive ground plan hypothesis. An interaction effect between nectar sugar concentration and ovariole number was observed in the backcross and high-strain bees. This result suggests a potential mechanism by which the ovary affects sucrose perception, which in turn influences foraging behaviour.