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Random sperm use and genetic effects on worker caste fate in Atta colombica leaf-cutting ants

Authors

  • LUKE HOLMAN,

    1. Centre for Social Evolution, Department of Biology, University of Copenhagen, Universitetsparken 15, 2100 Copenhagen, Denmark
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    • These authors contributed equally to the work.

    • Present address: Ecology, Evolution & Genetics, Research School of Biology, Australian National University, Canberra, ACT 0200, Australia.

  • MARLENE STÜRUP,

    1. Centre for Social Evolution, Department of Biology, University of Copenhagen, Universitetsparken 15, 2100 Copenhagen, Denmark
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    • These authors contributed equally to the work.

  • KALEVI TRONTTI,

    1. Department of Biosciences, PO Box 65, Viikinkaari 1, University of Helsinki, Helsinki 00014, Finland
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  • JACOBUS J. BOOMSMA

    1. Centre for Social Evolution, Department of Biology, University of Copenhagen, Universitetsparken 15, 2100 Copenhagen, Denmark
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Luke Holman, Fax: 61255573; E-mail: luke.holman@anu.edu.au

Abstract

Sperm competition can produce fascinating adaptations with far-reaching evolutionary consequences. Social taxa make particularly interesting models, because the outcome of sexual selection determines the genetic composition of groups, with attendant sociobiological consequences. Here, we use molecular tools to uncover some of the mechanisms and consequences of sperm competition in the leaf-cutting ant Atta colombica, a species with extreme worker size polymorphism. Competitive PCR allowed quantification of the relative numbers of sperm stored by queens from different males, and offspring genotyping revealed how sperm number translated into paternity of eggs and adult workers. We demonstrate that fertilization success is directly related to sperm numbers, that stored sperm are well-mixed and that egg paternity is constant over time. Moreover, worker size was found to have a considerable genetic component, despite expectations that genetic effects on caste fate should be minor in species with a low degree of polyandry. Our data suggest that sexual conflict over paternity is largely resolved by the lifetime commitment between mates generated by long-term sperm storage, and show that genetic variation for caste can persist in societies with comparatively high relatedness.

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