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Population genetics reveals origin and number of founders in a biological invasion

Authors

  • GENTILE FRANCESCO FICETOLA,

    1. Laboratoire d’Ecologie Alpine, UMR CNRS 5553, Université de Savoie. 73376 Le Bourget du Lac cedex France,
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    • Present address: Dipartimento di Scienze dell’Ambiente e del Territorio, Università di Milano Bicocca. Piazza della Scienza 1, 20126 Milano Italy.

  • AURELIE BONIN,

    1. Laboratoire d’Ecologie Alpine, UMR CNRS 5553, Université Joseph Fourier, 38041 Grenoble cedex 9, France
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  • CLAUDE MIAUD

    1. Laboratoire d’Ecologie Alpine, UMR CNRS 5553, Université de Savoie. 73376 Le Bourget du Lac cedex France,
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G. F. Ficetola, Fax: +33-(0)479758880; E-mail: francesco.ficetola@unimi.it

Abstract

Propagule pressure is considered the main determinant of success of biological invasions: when a large number of individuals are introduced into an area, the species is more likely to establish and become invasive. Nevertheless, precise data on propagule pressure exist only for a small sample of invasive species, usually voluntarily introduced. We studied the invasion of the American bullfrog, Rana catesbeiana, into Europe, a species that is considered a major cause of decline for native amphibians. For this major invader with scarce historical data, we used population genetics data (a partial sequence of the mitochondrial cytochrome b gene) to infer the invasion history and to estimate the number of founders of non-native populations. Based on differences between populations, at least six independent introductions from the native range occurred in Europe, followed by secondary translocations. Genetic diversity was strongly reduced in non-native populations, indicating a very strong bottleneck during colonization. We used simulations to estimate the precise number of founders and found that most non-native populations derive from less than six females. This capability of invasion from a very small number of propagules challenges usual management strategies; species with such ability should be identified at an early stage of introduction.

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