UNEXPLAINED SPLIT SEX RATIOS IN THE NEOTROPICAL PLANT-ANT, ALLOMERUS OCTOARTICULATUS VAR. DEMERARAE (MYRMICINAE): A TEST OF HYPOTHESES

Authors

  • Gabriel D. G. Debout,

    1. Ecology, Conservation, and Environment Center (ECEC), State Key Laboratory of Genetic Resources and Evolution, Kunming Institute of Zoology, Chinese Academy of Science, Kunming, Yunnan, 65022 China
    2. Centre for Ecology, Evolution, and Conservation (CEEC), School of Biological Sciences, University of East Anglia, Norwich NR4 7TJ, United Kingdom
    3. Department of Behavioural and Evolutionary Ecology, Université Libre de Bruxelles, 50 Av. F. Roosevelt, B-1050 Brussels, Belgium
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  • Megan E. Frederickson,

    1. Department of Biological Sciences, Stanford University, Stanford, California 94305
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    • 5

      Current address: Society of Fellows and Museum of Comparative Zoology, Harvard University, 26 Oxford Street, Cambridge, Massachusetts 02138.

  • Serge Aron,

    1. Department of Behavioural and Evolutionary Ecology, Université Libre de Bruxelles, 50 Av. F. Roosevelt, B-1050 Brussels, Belgium
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  • Douglas W. Yu

    1. Ecology, Conservation, and Environment Center (ECEC), State Key Laboratory of Genetic Resources and Evolution, Kunming Institute of Zoology, Chinese Academy of Science, Kunming, Yunnan, 65022 China
    2. Centre for Ecology, Evolution, and Conservation (CEEC), School of Biological Sciences, University of East Anglia, Norwich NR4 7TJ, United Kingdom
    3. E-mail: douglas.yu@uea.ac.uk
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Abstract

We investigated sex allocation in the Neotropical ant Allomerus octoarticulatus var. demerarae. Because Allomerus is a plant symbiont, we could make geographically extensive collections of complete colonies and of foundresses in saplings, allowing us to estimate not only population- and colony-level sex allocation but also colony resource levels and the relatednesses of competing ant foundresses. This species exhibits a strongly split sex ratio, with 80% of mature colonies producing ≥90% of one sex or the other. Our genetic analyses (DNA microsatellites) reveal that Allomerus has a breeding system characterized by almost complete monogyny and a low frequency of polyandry. Contrary to theoretical explanations, we find no difference in worker relatedness asymmetries between female- and male-specialist colonies. Furthermore, no clear link was found between colony sex allocation and life history traits such as the number of mates per queen, or colony size, resource level, or fecundity. We also failed to find significant support for male production by workers, infection by Wolbachia, local resource competition, or local mate competition. We are left with the possibility that Allomerus exhibits split sex ratios because of the evolution of alternative biasing strategies in queens or workers, as recently proposed in the literature.

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