Data from: Chemical communication is not sufficient to explain reproductive inhibition in the bumblebee Bombus impatiens

Reproductive division of labour is a hallmark of eusociality, but disentangling the underlying proximate mechanisms can be challenging. In bumblebees, workers isolated from the queen can activate their ovaries and lay haploid, male eggs. We investigated if volatile, contact, visual or behavioural cues produced by the queen or brood mediate reproductive dominance in Bombus impatiens. Exposure to queen-produced volatiles, brood-produced volatiles and direct contact with pupae did not reduce worker ovary activation; only direct contact with the queen could reduce ovary activation. We evaluated behaviour, physiology and gene expression patterns in workers that were reared in chambers with all stages of brood and a free queen, caged queen (where workers could contact the queen, but the queen was unable to initiate interactions) or no queen. Workers housed with a caged queen or no queen fully activated their ovaries, whereas ovary activation in workers housed with a free queen was completely inhibited. The caged queen marginally reduced worker aggression and expression of an aggression-associated gene relative to queenless workers. Thus, queen-initiated behavioural interactions appear necessary to establish reproductive dominance. Queen-produced chemical cues may function secondarily in a context-specific manner to augment behavioural cues, as reliable or honest signal.

生殖劳动分工（reproductive division of labour）是真社会性（eusociality）的标志性特征，但解析其背后的近因调控机制仍颇具挑战。在熊蜂（bumblebees）中，与蜂后隔离的工蜂可激活卵巢并产下单倍体雄性卵（haploid male eggs）。本研究探究了蜂后或蜂子产生的挥发性线索（volatile cues）、接触性线索（contact cues）、视觉线索（visual cues）或行为线索（behavioural cues）是否介导了光亮熊蜂（Bombus impatiens）的生殖支配地位（reproductive dominance）。
研究发现，暴露于蜂后分泌的挥发性物质、蜂子产生的挥发性物质，以及直接接触蛹态个体，均未抑制工蜂的卵巢激活；仅直接接触蜂后才能有效抑制卵巢激活。后续实验中，我们将工蜂饲养于分别搭载各发育阶段蜂子与自由活动蜂后、笼养蜂后（工蜂可接触蜂后，但蜂后无法主动发起互动）或无蜂后的饲养舱内，对工蜂的行为、生理及基因表达模式进行评估。结果显示，饲养于笼养蜂后或无蜂后环境中的工蜂卵巢完全激活，而饲养于自由蜂后环境中的工蜂卵巢激活则被完全抑制。相较于无蜂后工蜂，笼养蜂后仅小幅降低了工蜂的攻击行为与攻击相关基因（aggression-associated gene）的表达水平。
由此可见，蜂后主动发起的行为互动似乎是建立生殖支配地位的必要条件。蜂后产生的化学线索或许仅在特定情境下发挥辅助作用，用以强化行为线索的可靠信号或诚实信号效应。