Abstract
In ants, winged queens that are specialized for independent colony foundation can be replaced by wingless reproductives better adapted for colony fission. We studied this shift in reproductive strategy by comparing two Mystrium species from Madagascar using morphometry, allometry and dissections. Mystrium rogeri has a single dealate queen in each colony with a larger thorax than workers and similar mandibles that allow these queens to hunt during non-claustral foundation. In contrast, Mystrium ‘red’ lacks winged queens and half of the female adults belong to a wingless ‘intermorph’ caste smaller and allometrically distinct from the workers. Intermorphs have functional ovaries and spermatheca while those of workers are degenerate. Intermorphs care for brood and a few mate and reproduce making them an all-purpose caste that takes charge of both work and reproduction. However, their mandibles are reduced and inappropriate for hunting centipedes, unlike the workers’ mandibles. This together with their small thorax disallow them to perform independent colony foundation, and colonies reproduce by fission. M. rogeri workers have mandibles polymorphic in size and shape, which allow for all tasks from brood care to hunting. In M. ‘red’, colonial investment in reproduction has shifted from producing expensive winged queens to more numerous helpers. M. ‘red’ intermorphs are the first case of reproductives smaller than workers in ants and illustrate their potential to diversify their caste system for better colonial economy.
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Acknowledgements
We thank M. Beekman, F. Ito and D. Wheeler for the helpful comments on the manuscript. F. Ito provided unpublished data about M. camillae. We are grateful to Brian Fisher’s team in Madagascar for the field assistance and the warm welcome. This work was supported in part by the National Geographic Society grant n° 7617-04, National Science Foundation grant n° DEB-0344731 to B.L. Fisher and P.S. Ward and Laboratoire d’Ecologie CNRS UMR 7625. Research and export permits were issued by the Association Nationale pour la Gestion des Aires Protégées, République de Madagascar.
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Molet, M., Peeters, C. & Fisher, B.L. Winged queens replaced by reproductives smaller than workers in Mystrium ants. Naturwissenschaften 94, 280–287 (2007). https://doi.org/10.1007/s00114-006-0190-2
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DOI: https://doi.org/10.1007/s00114-006-0190-2