The function of polydomy: the ant Crematogaster torosa preferentially forms new nests near food sources and fortifies outstations
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Many ant species are polydomous, forming multiple spatially segregated nests that exchange workers and brood. However, why polydomy occurs is still uncertain. We investigated whether colonies of Crematogaster torosa form new polydomous nests to better exploit temporally stable food resources. Specifically, we tested the effect of food presence or absence and distance on the likelihood that colonies would form a new nest. Because this species also forms little-known structures that house only workers without brood (outstations), we also compared the function of this structure with true nests. Laboratory-reared colonies were connected to a new foraging arena containing potential nest sites with or without food for 4 months. When food was present, most colonies formed polydomous nests nearby and the remainder formed outstations. When food was absent, the behavior of colonies differed significantly, frequently forming outstations but never polydomous nests. Distance had no effect on the type of structure formed, but when food was present, a larger proportion of the workforce moved shorter distances. Workers often fortified the entrances to both structures and used them for storage of dried insect tissue (“jerky”). In an investigation of spatial fidelity, we found that workers on the between-nest trail were associated with the original nest, whereas workers collecting food were more likely to be associated with the new nest or outstation. C. torosa appears to have a flexible colony structure, forming both outstations and polydomous nests. Polydomous nests in this species were associated with foraging and were only formed near food resources.
KeywordsAnts Polydomy Outstations Social insects Collective behavior Foraging
We thank Mary Price, Emily Jones, Jenny Jandt, Tuan Cao, Nhi Duong, Kim Franklin, Anne Estes, Margaret Couvillon, Aimee Dunlap, Martha Hunter, Dan Papaj, Cédric Devigne, and two anonymous reviewers for comments on this manuscript, and Emily Kaleugher for laboratory assistance. We would also like to thank the Center for Insect Science at the University of Arizona and National Science Foundation grant no. IOS 0841756 for funding this research.
Declaration of integrity
These experiments comply with the current laws of the United States of America. The authors declare that they have no conflict of interest.
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