Abstract
Task partitioning allows for efficient coordination of behavior in social insect colonies. Many task allocation studies focus on social insect species with discrete morphological worker subcastes, such as those possessing major and minor workers with strongly differentiated body plans. Much less is known about task partitioning among size-variable workers lacking discrete morphological subcastes. We investigated task fidelity and its correlation with worker size in Formica species with differing degrees of body size variation. During a mark-recapture study that focused on three worker tasks (honeydew collection, nest building, and protein foraging) across 2 days, 98.6% of 3570 recaptured workers exhibited task fidelity. In species with high levels of worker size variation, worker size is strongly correlated with task performance. This size-task correlation is weaker, but still present, in species with less variably sized workers. Our results suggest that Formica use size-based task partitioning, a form of morphological polyethism. We expect social insects with and without discrete morphological worker subcastes to differ in ontogeny, evolutionary history, and degree of behavioral flexibility. Identifying the scope of variation in task partitioning mechanisms will facilitate comparative studies, thereby elucidating evolutionary histories and outcomes of alternative strategies.
Significance statement
Division of labor is thought to increase the efficiency and success of animal societies by allowing the performance of multiple tasks in parallel, rather than sequentially. We investigated the task partitioning strategy employed by an ecologically dominant ant genus characterized by continuous worker size variation but lacking discrete morphological worker subcastes. We show that several species employ a form of morphological polyethism, wherein individuals specialize in tasks according to body size. Size-mediated morphological polyethism in the absence of discrete morphological worker subcastes has been demonstrated in a few other social insects. However, this task allocation strategy is likely more common than previously recognized, as most insect societies display natural worker size variation. Further, we argue that it is important to distinguish between size- and subcaste-based morphological polyethism. Alternative task partitioning strategies are likely to impact animal societies’ resilience to environmental perturbations, which are becoming increasingly common in the face of global change.
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Data availability
The behavioral and morphological data generated and analyzed for this study are available on Dryad, https://doi.org/10.6086/D1D965. The genomic data generated and analyzed for this study are available on NCBI GenBank, https://www.ncbi.nlm.nih.gov/bioproject/SUB6698223.
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Acknowledgments
We express sincere gratitude for the field assistance provided by Christine Sosiak, without whom this work would not have been possible. We thank Alan Brelsford, Daniel Pierce, Madison Sankovitz, Aldo de la Mora Rodríguez, Amaranta Fontcuberta, S. Hollis Woodard, and two anonymous reviewers for their thoughtful comments and suggestions. We also thank the University of Calgary Biogeoscience Institute’s Barrier Lake Field Station and Kananaskis Emergency Service for accommodation and support throughout our field season.
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This research was funded by the ACA Grants in Biodiversity (supported by the Alberta Conservation Association) and MW was supported in part by a fellowship from UCR NICE (NRT for Integrated Computational Entomology) National Science Foundation Award 1631776.
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Both authors conceived and designed the study and contributed to writing. MW carried out the fieldwork and analyses, with contributions and guidance from JP. Both authors contributed critically to writing and revising the manuscript and gave final approval for submission.
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West, M., Purcell, J. Task partitioning in ants lacking discrete morphological worker subcastes. Behav Ecol Sociobiol 74, 66 (2020). https://doi.org/10.1007/s00265-020-02845-w
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DOI: https://doi.org/10.1007/s00265-020-02845-w