Can things get worse when an invasive species hybridizes? The harlequin ladybird Harmonia axyridis in France as a case study.

Benoît Facon,Laurent Crespin,Arnaud Estoup,Eric Lombaert,Anne Loiseau,Alexandra Magro

doi:10.1111/j.1752-4571.2010.00134.x

Abstract

So far, only a few studies have explicitly investigated the consequences of admixture for the adaptative potential of invasive populations. We addressed this question in the invasive ladybird Harmonia axyridis. After decades of use as a biological control agent against aphids in Europe and North America, H. axyridis recently became invasive in four continents and has now spread widely in Europe. Despite this invasion, a flightless strain is still sold as a biological control agent in Europe. However, crosses between flightless and invasive individuals yield individuals able to fly, as the flightless phenotype is caused by a single recessive mutation. We investigated the potential consequences of admixture between invasive and flightless biological control individuals on the invasion in France. We used three complementary approaches: (i) population genetics, (ii) a mate-choice experiment, and (iii) a quantitative genetics experiment. The invasive French population and the biological control strain showed substantial genetic differentiation, but there are no reproductive barriers between the two. Hybrids displayed a shorter development time, a larger size and a higher genetic variance for survival in starvation conditions than invasive individuals. We discuss the potential consequences of our results with respect to the invasion of H. axyridis in Europe.

Highlights

Hybridization takes place in a very wide range of organisms (Barton and Hewitt 1985, Dowling & Secor 1997, Mallet 2005) and may play an active role in a variety of evolutionary processes ranging from local adaptation to speciation (Stebbins 1959; Arnold 1992; Barton 2001; Rieseberg et al 2003)
We found that the BIO and INV populations were genetically substantially differentiated with FST = 0.13 (P < 0.0001)
Our study clearly demonstrates that admixture between individuals from the French invasive population and from the flightless biological control strain of the harlequin ladybird could potentially alter the invasion process

Summary

Introduction

Hybridization (interbreeding between genetically differentiated lineages) takes place in a very wide range of organisms (Barton and Hewitt 1985, Dowling & Secor 1997, Mallet 2005) and may play an active role in a variety of evolutionary processes ranging from local adaptation to speciation (Stebbins 1959; Arnold 1992; Barton 2001; Rieseberg et al 2003). In the field of invasion biology, hybridization is seen as a potential stimulus for the evolution of invasiveness (Ellstrand and Schierenbeck 2000; Lavergne and Molofsky 2007; Ryan et al 2009; Blair and Hufbauer 2010). Crosses between individuals from genetically differentiated populations of the same species (i.e. admixture, Ellstrand and Schierenbeck 2000; Culley and Hardiman 2009) are considered hybridization (Wolfe et al 2007; Culley and Hardiman 2009). An increasing number of studies document biological invasions resulting from multiple introductions from distinct populations that bring together genetically differentiated individuals into a a 2010 Blackwell Publishing Ltd 4 (2011) 71–88

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