Diploid male production in a leaf-cutting ant

Authors

  • SOPHIE ARMITAGE,

    1. Department of Biology, Centre for Social Evolution, University of Copenhagen, Universitetsparken 15, 2100 Copenhagen, Denmark
    Search for more papers by this author
    • *

      Current address: Institute for Evolution and Biodiversity, Westfälische Wilhelms University, Hüfferstrasse 1, 48149 Münster, Germany.

  • JACOBUS BOOMSMA,

    1. Department of Biology, Centre for Social Evolution, University of Copenhagen, Universitetsparken 15, 2100 Copenhagen, Denmark
    Search for more papers by this author
  • BORIS BAER

    Corresponding author
    1. Department of Biology, Centre for Social Evolution, University of Copenhagen, Universitetsparken 15, 2100 Copenhagen, Denmark
    Search for more papers by this author
    • Current address: Centre for Evolutionary Biology, School of Animal Biology (MO92), The University of Western Australia, 6009 Crawley, Australia.


Boris Baer, ARC Centre of Excellence in Plant Energy Biology, The University of Western Australia, 6009 Crawley, Australia.

Abstract

1. In haplodiploid social insects where males are haploid and females are diploid, inbreeding depression is expressed as the production of diploid males when homozygosity at the sex-determining locus results in the production of diploid individuals with a male phenotype. Diploid males are often assumed to have reduced fitness compared with their haploid brothers.

2. While studying the reproductive biology of a leaf-cutting ant, Atta sexdens, in Gamboa, Republic of Panama, we detected the presence of a larger male morph. Using microsatellite markers we were able to confirm that the large male morph was diploid in 87% of cases.

3. We infer that the Gamboa population of A. sexdens experiences inbreeding depression because diploid males were found in three out of five mature colonies. However, their frequencies were relatively low because queens were multiply mated and our estimates suggest that many diploid male larvae may not survive to adulthood.

4. We measured two traits potentially linked to male reproductive success: sperm length and sperm number, and showed that diploid males produced fewer but longer sperm. These results provide indirect evidence that diploid male reproductive success would be reduced compared with haploid males if they were able to copulate.

5. We conclude that diploid male production is likely to affect the fitness of A. sexdens queens with a matched mating, as these males are produced at the cost of workers and, if the colony survives to reach mature size, also gynes.

Ancillary