Regulation of Reproduction in the Primitively Eusocial Wasp Ropalidia marginata: on the Trail of the Queen Pheromone
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Queens and workers are not morphologically differentiated in the primitively eusocial wasp, Ropalidia marginata. Upon removal of the queen, one of the workers becomes extremely aggressive, but immediately drops her aggression if the queen is returned. If the queen is not returned, this hyper-aggressive individual, the potential queen (PQ), will develop her ovaries, lose her hyper-aggression, and become the next colony queen. Because of the non-aggressive nature of the queen, and because the PQ loses her aggression by the time she starts laying eggs, we hypothesized that regulation of worker reproduction in R. marginata is mediated by pheromones rather than by physical aggression. Based on the immediate loss of aggression by the PQ upon return of the queen, we developed a bioassay to test whether the queen’s Dufour’s gland is, at least, one of the sources of the queen pheromone. Macerates of the queen’s Dufour’s gland, but not that of the worker’s Dufour’s gland, mimic the queen in making the PQ decrease her aggression. We also correctly distinguished queens and workers of R. marginata nests by a discriminant function analysis based on the chemical composition of their respective Dufour’s glands.
Key WordsRopalidia marginata Queen pheromone Potential queen Dufour’s gland Reproductive monopoly
We thank the Department of Science and Technology, the Department of Biotechnology, the Council for Scientific and Industrial Research and the Ministry of Environment and Forests, Government of India for financial assistance, and Robin Crewe for helpful comments and encouragement. We also thank Anjali Rajasekharan, Pooja Muralidharan and Gautam Pramanik, Centre for Ecological Sciences, Indian Institute of Science, Bangalore, for technical assistance with the GC-MS analyses and, Prasanta Das, Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore, for providing useful suggestions regarding interpretation of mass spectra. AB carried out the behavioral observations. SAD, KC, and AM did the dissections and prepared the extracts. AM carried out the chemical analysis, with help and guidance from DGN and AH. The paper was co-written by AB, AM, and RG, and RG supervised the overall work. All experiments reported here comply with the current laws of the country in which they were performed.
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