Abstract
Honeybee workers develop from fertilised eggs, but those reared in a queenless colony develop into ‘rebel’ workers, which are more queen-like than typical workers. Rebels develop after an old queen leaves with a swarm and before a new queen hatches. We hypothesised that larval food lacking queen mandibular pheromones trigger the rebel phenotype. Larvae reared under queenright or queenless conditions were additionally fed with water or a drop of macerated queen mandibular glands. After following development of the bees and subjecting them to dissection, we found that those reared with a queen or fed the macerated glands under queenless conditions developed into typical workers. Only those workers reared without a queen and without macerated glands added to their food developed into rebels; these rebels had more ovarioles, smaller hypopharyngeal glands, and larger mandibular and Dufour’s glands than did typical workers. This is the first evidence that larval perception of the presence or absence of queen pheromones causes an alternative development strategy.
Highlights
Reproductive division of labour and the development of a non-reproductive worker caste are the most important features of eusocial insects and fundamental problems in evolutionary biology (Toth and Robinson 2007; Van Oystaeyen et al 2014)
We examined in this study whether cues indicating the presence or absence of a queen are detected from food by worker larvae directly and whether these larvae adjust their strategy namely by developing into normal workers if queen mandibular pheromones (QMPs) are present in the food or into rebels if these pheromones are absent
We found that in each of the colonies, the anatomical characters of the workers that had developed from the larvae with QMPs in their food, that is, those reared under the queenright condition and those reared in the queenless subunits that had macerated queen mandibular glands added to their food, did not differ from each other (Figure 1)
Summary
Reproductive division of labour and the development of a non-reproductive worker caste are the most important features of eusocial insects and fundamental problems in evolutionary biology (Toth and Robinson 2007; Van Oystaeyen et al 2014). The best model for investigating these issues is the honeybee (Apis mellifera ) colony, where queen mandibular pheromones (QMPs) play a crucial regulatory role in inhibiting ovarian development in adult workers and suppressing their reproduction (Van Oystaeyen et al 2014). Honeybee queen signals are transferred via trophallaxis, i.e. the exchange of liquid food among colony members (Seeley 1979). These cues can change the feeding strategy of nurses towards larvae (Kuwabara 1948; Woyke 1999). We examined in this study whether cues indicating the presence or absence of a queen are detected from food by worker larvae directly and whether these larvae adjust their strategy namely by developing into normal workers if QMPs are present in the food or into rebels if these pheromones are absent
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