Do Bumble Bee, Bombus impatiens, Queens Signal their Reproductive and Mating Status to their Workers?
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Reproduction in social insect societies reflects a delicate balance between cooperation and conflict over offspring production, and worker reproduction is widespread even in species showing strong reproductive skew in favor of the queen. To navigate these conflicts, workers are predicted to develop the means to estimate the queen’s fecundity - potentially through behavioral and/or chemical cues - and to adjust their reproduction to maximize their fitness. Here, we introduced bumble bee, Bombus impatiens, workers to queens of different mating and reproductive status and examined worker reproduction and expression levels of two genes which were previously shown to be sensitive to the presence of the queen, vitellogenin and Krüppel-homolog 1. We further explored whether the queen’s chemical secretion alone is sufficient to regulate worker reproduction, aggression and gene expression. We found that worker ovary activation was inhibited only in the presence of egg-laying queens, regardless of their mating status. Workers reared in the presence of newly-mated queens showed intermediate vitellogenin expression levels relative to workers reared with mated egg-laying and virgin queens. However, none of the whole-body chemical extracts of any of the queen treatment groups affected ovary activation, aggressive behavior, or gene expression in workers. Our findings indicate that only the presence of a freely-behaving, egg-laying queen can fully inhibit worker reproduction. It remains to be determined if workers detect differences in queen mating status and fecundity through differences in the queens’ behavior alone or through the queen’s behavior in concert with fertility signals.
KeywordsReproduction Pheromones Signals Aggression Gene expression
We would like to thank the Grozinger lab for helpful discussions and Nate McCartney (Tumlinson Lab, Penn State University) for assistance in designing the equipment used in Experiment 2. M. P. was supported by a Bunton-Waller Graduate Award from Penn State University. E.A. was supported by a United States - Israel Binational Agricultural Research and Development Fund Vaadia–BARD Postdoctoral Fellowship (FI-49113). This research was supported by funding from the United States–Israel Binational Science Foundation (grant #2013104) to C.M.G., N.A. and A.H.
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