Abstract
The “reproductive ground plan” hypothesis (RGPH) proposes that reproductive division of labour in social insects had its antecedents in the ancient gene regulatory networks that evolved to regulate the foraging and reproductive phases of their solitary ancestors. Thus, queens express traits that are characteristic of the reproductive phase of solitary insects, whereas workers express traits characteristic of the foraging phase. The RGPH has also been extended to help understand the regulation of age polyethism within the worker caste and more recently to explain differences in the foraging specialisations of individual honey bee workers. Foragers that specialise in collecting proteinaceous pollen are hypothesised to have higher reproductive potential than individuals that preferentially forage for nectar because genes that were ancestrally associated with the reproductive phase are active. We investigated the links between honey bee worker foraging behaviour and reproductive traits by comparing the foraging preferences of a line of workers that has been selected for high rates of worker reproduction with the preferences of wild-type bees. We show that while selection for reproductive behaviour in workers has not altered foraging preferences, the age at onset of foraging of our selected line has been increased. Our findings therefore support the hypothesis that age polyethism is related to the reproductive ground plan, but they cast doubt on recent suggestions that foraging preferences and reproductive traits are pleiotropically linked.
Highlights
Two of the most challenging questions to students of social insects are the evolutionary origins of the worker caste [e.g., 1–6] and the regulation of division of labour within the worker caste [e.g., 7–13]
The ‘‘reproductive ground plan’’ hypothesis (RGPH) suggests that social insects evolved their queen and worker castes by modifying a gene network that once regulated the foraging and reproductive phases of solitary ancestors
We evaluated the RGPH by studying a line of honey bees selected for high rates of worker reproduction
Summary
Two of the most challenging questions to students of social insects are the evolutionary origins of the worker caste [e.g., 1–6] and the regulation of division of labour within the worker caste [e.g., 7–13]. Hunt and Amdam [18] proposed a modification of this idea, arguing that in Polistes wasps at least, queens and workers arise from two developmental pathways that characterise the bivoltine lifecycle of some solitary species (bivoltine RGPH, Table 1). They suggest that queens evolved via cooption of the gene regulatory networks that are switched on in late-emerging, second-generation individuals that diapause, and the worker caste from networks switched on in early-emerging first generation individuals that do not enter diapause
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