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Title: Complementarity of statistical treatments to reconstruct worldwide routes of invasion: The case of the Asian ladybird Harmonia axyridis

Author
item LOMBAERT, E - Institut National De La Recherche Agronomique (INRA)
item GUILLEMAUD, T - Institut National De La Recherche Agronomique (INRA)
item KOCH, R - University Of Minnesota
item FACON, B - Institut National De La Recherche Agronomique (INRA)
item GREZ, A - Institut National De La Recherche Agronomique (INRA)
item LOOMANS, A - Institut National De La Recherche Agronomique (INRA)
item MALAUSA, T - Institut National De La Recherche Agronomique (INRA)
item NEDVED, O - Institut National De La Recherche Agronomique (INRA)
item RHULE, E - Institut National De La Recherche Agronomique (INRA)
item ESTOUP, A - Institut National De La Recherche Agronomique (INRA)
item Lundgren, Jonathan

Submitted to: Molecular Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/28/2014
Publication Date: 12/11/2014
Citation: Lombaert, E., Guillemaud, T., Lundgren, J.G, Koch, R., Facon, B., Grez, A., Loomans, A., Malausa, T., Nedved, O., Rhule, E., Staverlokk, A., Steenberg, T., Estoup, A. 2014. Complementarity of statistical treatments to reconstruct worldwide routes of invasion: The case of the Asian ladybird Harmonia axyridis. Molecular Ecology. 23(24):5979-5997.

Interpretive Summary: The Asian ladybeetle (Harmonia axyridis) is a notorious invasive pest throughout much of the world, and has thus served as a model organism for understanding how biological invasions transpire. Our study uses advanced statistical to study the genetics of how and when the H. axyridis invasion progressed to produce its current distribution. Our experiments revealed that two North American populations served as the source for at least six other invasions throughout the world, and that occasionally these North American populations would hybridize with other genetic sources within a new geographic region. This work provides new tools to help scientists interested in tracking the routes of invasive species.

Technical Abstract: Technical Abstract. Molecular markers can provide clear insight into the introduction history of invasive species. However, inferences about recent introduction histories remain challenging, because of the stochastic demographic processes often involved. Approximate Bayesian computation (ABC) can help to overcome these problems, but such methods of inference require a prior understanding of population structure over the study area, necessitating the use of alternative methods and an intense sampling design. In this study, we made inferences about the worldwide invasion history of the ladybird Harmonia axyridis by various population genetics statistical methods, using a large set of sampling sites distributed over most of the native and invaded areas for this species. We evaluated the complementarity of the statistical methods and the consequences of using different sets of population samples for ABC inferences. We found that the worldwide Harmonia axyridis invasion has involved two bridgehead invasive populations in North America, which have served as the source populations for at least six independent introductions into other continents. We also identified several situations of genetic admixture between differentiated sources. Our results highlight the importance of coupling ABC methods with more traditional statistical approaches. We found that the choice of population samples could affect the conclusions of ABC analyses comparing possible scenarios. Approaches involving the performance of independent ABC analyses on several sample sets constitute a sensible solution, making it possible to avoid erroneous conclusions. This study provides biologists without expertise in this area with detailed methodological and conceptual guidelines for making inferences about invasion routes when dealing with a large number of sampling sites and complex population genetic structures.