Size-correlated division of labour and spatial distribution of workers in the driver ant, Dorylus molestus
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Driver ants (Dorylus spp.) show a high degree of worker polymorphism. Previous reports suggest that large Dorylus workers are specialised for defensive tasks. In this study, we first quantitatively tested whether there is a size-correlated division of defensive labour among workers. Second, we determined whether the spatial distribution of workers outside the nest can be predicted based on such size-specific differences in task allocation. We show that the division of defensive behaviour among different-sized workers is not strict. However, there is a significant correlation between worker size and the tendency to carry out defensive tasks. First, workers of larger size were more likely than smaller workers to participate in colony defence. Second, larger workers were more frequent near the nest containing the reproducing individuals and the brood. Finally, large workers were more common in open sections of the trail than in covered sections, which are likely to be less exposed to predators.
KeywordsNest Site Head Width Large Worker Small Worker Work Size
This study was conducted during a Darwin Course in Tropical Biology organised by the Tropical Biology Association (TBA). We thank the TBA, in particular Rosie Trevelyan, for their support. William Gotwald, Jr., kindly identified the ant specimens. We thank Thomas Flatt for helpful comments on earlier versions of the manuscript. C.B. was funded by the Swiss Study Foundation, the Olga and Joseph-Tomscik Foundation, and the British Ecological Society (BES). T.B. was supported by funds from the University of Oslo via Nils Christian Stenseth, and the BES. L.K. was funded by grants from the Swiss NSF.
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