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Evidence for widespread cryptic sexual generations in apparently purely asexual Andricus gallwasps

Authors

  • GRAHAM N. STONE,

    1. Institute of Evolutionary Biology, School of Biology, The King's Buildings, West Mains Road, Edinburgh EH9 3JT, UK,
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  • RACHEL J. ATKINSON,

    1. Institute of Evolutionary Biology, School of Biology, The King's Buildings, West Mains Road, Edinburgh EH9 3JT, UK,
    2. Charles Darwin Research Station, Puerto Ayora, Santa Cruz, Galapagos Islands, Ecuador,
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  • ANTONIS ROKAS,

    1. The Broad Institute of MIT and Harvard, 320 Charles Street, Cambridge, MA 02141, USA,
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  • JOSÉ-LUIS NIEVES ALDREY,

    1. Departamento de Biodiversidad y Biología Evolutiva Museo Nacional de Ciencias Naturales (CSIC) c/José Gutiérrez Abascal 2, Madrid, E-28006, Spain,
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  • GEORGE MELIKA,

    1. Systematic Parasitoid Laboratory, Plant Protection and Soil Conservation Service of County Vas, Ambrozy Setany 2, 9762 Tanakajd, Hungary,
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  • ZOLTAN Ács,

    1. Systematic Parasitoid Laboratory, Plant Protection and Soil Conservation Service of County Vas, Ambrozy Setany 2, 9762 Tanakajd, Hungary,
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  • GYÖRGY CSÓKA,

    1. Hungarian Forest Research Institute, Mátrafüred Research Station, 3232 Mátrafüred, Hungary,
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  • ALEXANDER HAYWARD,

    1. Institute of Evolutionary Biology, School of Biology, The King's Buildings, West Mains Road, Edinburgh EH9 3JT, UK,
    2. Department of Zoology, South Parks Road, Oxford OX1 3PS, UK,
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  • RICHARD BAILEY,

    1. Institute of Evolutionary Biology, School of Biology, The King's Buildings, West Mains Road, Edinburgh EH9 3JT, UK,
    2. Evolutionary Biology Centre, Uppsala University, Norbyvagen 18, SE 752 36 Uppsala, Sweden and
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  • CAROLINE BUCKEE,

    1. Institute of Evolutionary Biology, School of Biology, The King's Buildings, West Mains Road, Edinburgh EH9 3JT, UK,
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  • GILEAN A. T. McVEAN

    1. Department of Statistics, University of Oxford, 1 South Parks Road, Oxford OX1 3TG, UK
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Dr Graham Stone,. Fax: 0131 6506564; E-mail: graham.stone@ed.ac.uk

Abstract

Oak gallwasps (Hymenoptera, Cynipidae, Cynipini) are one of seven major animal taxa that commonly reproduce by cyclical parthenogenesis (CP). A major question in research on CP taxa is the frequency with which lineages lose their sexual generations, and diversify as purely asexual radiations. Most oak gallwasp species are only known from an asexual generation, and secondary loss of sex has been conclusively demonstrated in several species, particularly members of the holarctic genus Andricus. This raises the possibility of widespread secondary loss of sex in the Cynipini, and of diversification within purely parthenogenetic lineages. We use two approaches based on analyses of allele frequency data to test for cryptic sexual generations in eight apparently asexual European species distributed through a major western palaearctic lineage of the gallwasp genus Andricus. All species showing adequate levels of polymorphism (7/8) showed signatures of sex compatible with cyclical parthenogenesis. We also use DNA sequence data to test the hypothesis that ignorance of these sexual generations (despite extensive study on this group) results from failure to discriminate among known but morphologically indistinguishable sexual generations. This hypothesis is supported: 35 sequences attributed by leading cynipid taxonomists to a single sexual adult morphospecies, Andricus burgundus, were found to represent the sexual generations of at least six Andricus species. We confirm cryptic sexual generations in a total of 11 Andricus species, suggesting that secondary loss of sex is rare in Andricus.

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