Age-related division of labor occurs in ants at the earliest stages of colony initiation

Abstract

Mature colonies of many social insect species exhibit division of labor (DOL) where individual workers specialize in doing only a subset of the multiple tasks needed to maintain homeostasis. In newly initiated ant colonies, however, the first workers (called nanitics) are few in number and much smaller in size than those in mature colonies. This limited workforce must perform most of the tasks of mature colonies, but it is unknown if they also exhibit DOL. In this study, we tracked several inside-nest and outside-nest behaviors of nanitics in incipient Pogonomyrmex rugosus colonies. DOL arises in these colonies, whereby the relatively oldest workers (even if only by a few hours) are biased towards foraging, while younger nanitics concentrate on brood care. The addition of new nanitics shifts behavior in the oldest individual away from brood care but does not immediately increases its foraging. Conversely, nanitics left alone due to mortality of nest-mates forage more, but do not reduce brood care. The results suggest P. rugosus nanitics follow an age-related task specialization pattern that is broadly similar to mature colonies. The nanitic life stage may be, however, unique for ants in how fine-grained the DOL is in terms of absolute age differences and flexibility for task switching.

Significance statement

The ecological success of ants is thought to be facilitated by workers dividing their labor across tasks. Commonplace in mature colonies is that individuals will perform safer, within-nest tasks such as brood care when young, and shift as they age towards riskier, outside-nest tasks such as foraging. Because many do the same task, the death of any single worker has minimal effect. We show, for the first time, a similar age-related, task specialization pattern also occurs in newly founded colonies. In this earliest life, history stage workers are small and few in number, precluding the massive task redundancy that characterizes mature colonies. Nevertheless, a division of labor correlating with relative age differences arises even when workers differ in age by only a few hours. This supports the hypothesis that a similar developmental pathway for task allocation in worker behavior occurs at all stages in colony life history.

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Data availability

Data for each colony and observation will be submitted to Dryad upon manuscript acceptance. Data can be provided upon request.

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Acknowledgments

We thank Robert A. Johnson and Juergen Gadau for generously supplying us with P. rugosus foundresses from Arizona and Jennifer Fewell for supplying the lab space to carry out observations. We extend our appreciation to Kelsey Cozzolino and Jennifer DePew who conducted many of the behavioral observations for this study.

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BLE and PN both conceived the idea. BLE designed the experiment and collected the data. PN did the statistical analyses. BLE and PN both wrote the paper.

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Correspondence to Peter Nonacs.

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Enzmann, B.L., Nonacs, P. Age-related division of labor occurs in ants at the earliest stages of colony initiation. Behav Ecol Sociobiol 75, 35 (2021). https://doi.org/10.1007/s00265-021-02974-w

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Keywords

  • Pogonomyrmex
  • Harvester ant
  • Nanitic
  • Age polyethism