Osnat Malka, Shiri Shnieor, Tamar Katzav-Gozansky, and Abraham Hefetz. Department of Zoology, Tel Aviv University, Ramat Aviv, Tel Aviv, Israel
The honeybee (Apis mellifera) constitutes a classical example of reproductive skew whereby the queen is the major egg layer, while workers are largely sterile. Under queenright conditions workers maximize their inclusive fitness by selectively rearing the queen-born males. However, under queenless-hopeless conditions, workers gain maximal fitness by rearing sons, and consequently develop ovaries and lay unfertilized, male eggs. This transition from cooperation and sterility to selfish behavior and egg-laying encompasses all levels of organization, from competition through aggression, via mass egg-laying to biochemical shift in pheromone biosynthesis from worker- to queen-like chemical bouquet. Here we investigated the behavioral, reproductive and pheromonal plasticity in workers, and their possible role in queen-worker and worker-worker competition. To assess worker-worker competition we observed callow workers reared as queenless groups for two weeks. Soon after group establishment aggression erupted, and was directed towards workers with developed ovaries mainly by workers with undeveloped ovaries. Analyses of Dufour’s and mandibular gland secretions revealed that the attacked workers had higher levels of queen-like secretion compared to the attacking or passive workers. This indicates that either or both pheromones disclose the fertility and perhaps hierarchical status of the attacked workers. To assess whether worker fertility and royal pheromone production are reversible we induced ovary activation and queen pheromone production in workers by rearing them as queenless groups, and subsequently reintroduced them into micro-colonies of different social structures for one week. Such workers if reintroduced into queenright, but not queenless colonies showed a clear regression in ovary development and reversion to worker-like pheromones. These results emphasize the robustness of the coupling between ovary activation and royal pheromone production. It further emphasizes the powerful effect of the queen and her pheromones on worker physiology and behavior.
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