Ant queens are among the most long-lived insects known1,2. They mate early in adult life and maintain millions of viable sperm in their sperm storage organ until they die many years later3,4. Because they never re-mate, the reproductive success of queens is ultimately sperm-limited, but it is not known what selective forces determine the upper limit to sperm storage. Here we show that sperm storage carries a significant cost of reduced immunity during colony founding. Newly mated queens of the leaf-cutting ant Atta colombica upregulate their immune response shortly after completing their nest burrow, probably as an adaptive response to a greater exposure to pathogens in the absence of grooming workers. However, the immune response nine days after colony founding is negatively correlated with the amount of sperm in the sperm storage organ, indicating that short-term survival is traded off against long-term reproductive success. The immune response was lower when more males contributed to the stored sperm, indicating that there might be an additional cost of mating or storing genetically different ejaculates.
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We thank D. R. Nash for advice on statistical issues; C. Andersen and S. Mathiasen for assistance with DNA work; S. Mathiasen and D. J. C. Kronauer for advice on DNA work; S. P. A. den Boer, M. Poulsen, A. M. Schmidt, J. Thomas and L. V. Ugelvig for assistance in the field, and P. D'Ettorre, D. R. Nash, J. S. Pedersen, B. Baer-Imhoof and L. W. Simmons for comments on the manuscript. This study was supported by the Swiss National Science Foundation (stipend for advanced scientists to B.B.), the EU Research-Training Network INSECTS, the Carlsberg Foundation and a Marie Curie Intra-European Fellowship (postdoctoral stipends to S.A.O.A.), the Danish Natural Science Research Council (B.B. and J.J.B.) and the Danish National Research Foundation (J.J.B. and S.A.O.A.). We thank the Smithsonian Tropical Research Institute in Panama for facilities and logistical support, and the Autoridad Nacional de Ambiente (ANAM) of Panama for issuing collection and export permits.
Reprints and permissions information is available at npg.nature.com/reprintsandpermissions. The authors declare no competing financial interests.
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Baer, B., Armitage, S. & Boomsma, J. Sperm storage induces an immunity cost in ants. Nature 441, 872–875 (2006). https://doi.org/10.1038/nature04698
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