Abstract
Several ant species vary in the number of queens per colony, yet the causes and consequences of this variation remain poorly understood. In previous experiments, we found that Formica selysi workers originating from multiple-queen (=polygyne) colonies had a lower resistance to a fungal pathogen than workers originating from single-queen (=monogyne) colonies. In contrast, group diversity improved disease resistance in experimental colonies. This discrepancy between field and experimental colonies suggested that variation in social structure in the field had antagonistic effects on worker resistance, possibly through a down-regulation of the immune system balancing the positive effect of genetic diversity. Here, we examined if workers originating from field colonies with alternative social structure differed in three major components of their immune system. We found that workers from polygyne colonies had a lower bacterial growth inhibitory activity than workers from monogyne colonies. In contrast, workers from the two types of colonies did not differ significantly in bacterial cell wall lytic activity and prophenoloxidase activity. Overall, the presence of multiple queens in a colony correlated with a slight reduction in one inducible component of the immune system of individual workers. This reduced level of immune defence might explain the lower resistance of workers originating from polygyne colonies despite the positive effect of genetic diversity. More generally, these results indicate that social changes at the group level can modulate individual immune defences.
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Acknowledgments
We thank Céline Fioravanti and Antoine Burnier for their important contribution to this study during their undergraduate training, Yannick Moret for help with immunological techniques, Laurent Keller and an anonymous reviewer for comments on the manuscript. This research was supported by grants 3100A0-104118, 3100AO-108263 and 31003A_125306 from the Swiss National Science Foundation.
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Castella, G., Christe, P. & Chapuisat, M. Covariation between colony social structure and immune defences of workers in the ant Formica selysi . Insect. Soc. 57, 233–238 (2010). https://doi.org/10.1007/s00040-010-0076-3
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DOI: https://doi.org/10.1007/s00040-010-0076-3