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Species introduction promotes hybridization and introgression in Coregonus: is there sign of selection against hybrids?

Authors

  • KIMMO K. KAHILAINEN,

    1. Kilpisjärvi Biological Station, University of Helsinki, Käsivarrentie 14622, FI-99490 Kilpisjärvi, Finland
    2. Department of Environmental Sciences, PO Box 65, FI-00014 University of Helsinki, Finland
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  • KJARTAN ØSTBYE,

    1. Department of Biology, Centre for Ecological and Evolutionary Synthesis (CEES), University of Oslo, PO Box 1066, Blindern, NO-0316 Oslo, Norway
    2. Department of Forestry and Wildlife Management, Hedmark University College, Campus Evenstad, NO-2418 Elverum, Norway
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  • CHRIS HARROD,

    1. Department of Ecological Genetics, Max Planck Institute for Limnology, D-24302 Plön, Germany
    2. School of Biological Sciences, Medical Biology Centre, Queen’s University Belfast, 97 Lisburn Road, Belfast BT9 7BL, UK
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  • TAKAHITO SHIKANO,

    1. Department of Biosciences, Ecological Genetics Research Unit, PO Box 65, FI-00014 University of Helsinki, Finland
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  • TOMMI MALINEN,

    1. Department of Environmental Sciences, PO Box 65, FI-00014 University of Helsinki, Finland
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  • JUHA MERILÄ

    1. Department of Biosciences, Ecological Genetics Research Unit, PO Box 65, FI-00014 University of Helsinki, Finland
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Kimmo K. Kahilainen, Fax: +358 16 3202100; E-mail: kimmo.kahilainen@helsinki.fi

Abstract

Species introductions are considered one of the major drivers of biodiversity loss via ecological interactions and genetic admixture with local fauna. We examined two well-recognized fish species, native whitefish (Coregonus lavaretus) and introduced vendace (Coregonus albula), as well as their morphological hybrids in a single lake to test for selection against hybrids and backcrosses in the wild. A representative random subsample of 693 individuals (27.8%) was taken from the total catch of coregonids. This subsample was examined with the aim to select c. 50 individuals of pure whitefish (n = 52), pure vendace (n = 55) and putative hybrid (n = 19) for genetic analyses. The subsequent microsatellites and mitochondrial (mt) DNA analyses provided compelling evidence of hybridization and introgression. Of the 126 fish examined, four were found to be F1, 14 backcrosses to whitefish and seven backcrosses to vendace. The estimates of historical gene flow suggested higher rates from introduced vendace into native whitefish than vice versa, whereas estimates of contemporary gene flow were equal. Mitochondrial introgression was skewed, with 18 backcrosses having vendace mtDNA and only three with whitefish mtDNA. Hybrids and backcrosses had intermediate morphology and niche utilization compared with parental species. No evidence of selection against hybrids or backcrosses was apparent, as both hybrid and backcross growth rates and fecundities were high. Hybrids (F1) were only detected in 2 year-classes, suggesting temporal variability in mating between vendace and whitefish. However, our data show that hybrids reached sexual maturity and reproduced actively, with backcrosses recorded from six consecutive year-classes, whereas no F2 individuals were found. The results indicate widespread introgression, as 10.8% of coregonids were estimated to be backcrosses.

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