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Bridgehead Effect in the Worldwide Invasion of the Biocontrol Harlequin Ladybird

March 17th, 2010

Recent studies of the routes of worldwide introductions of alien organisms suggest that many widespread invasions could have stemmed not from the native range, but from a particularly successful invasive population, which serves as the source of colonists for remote new territories. We call here this phenomenon the invasive bridgehead effect. Evaluating the likelihood of such a scenario is heuristically challenging. We solved this problem by using approximate Bayesian computation methods to quantitatively compare complex invasion scenarios based on the analysis of population genetics (microsatellite variation) and historical (first observation dates) data. We applied this approach to the Harlequin ladybird Harmonia axyridis (HA), a coccinellid native to Asia that was repeatedly introduced as a biocontrol agent without becoming established for decades. We show that the recent burst of worldwide invasions of HA followed a bridgehead scenario, in which an invasive population in eastern North America acted as the source of the colonists that invaded the European, South American and African continents, with some admixture with a biocontrol strain in Europe. This demonstration of a mechanism of invasion via a bridgehead has important implications both for invasion theory (i.e., a single evolutionary shift in the bridgehead population versus multiple changes in case of introduced populations becoming invasive independently)and for ongoing efforts to manage invasions by alien organisms (i.e., heightened vigilance against invasive bridgeheads).

Competing Interests: The authors have declared that no competing interests exist.

Funding: This work was supported by grants from the Agence Nationale de la Recherche (ANR-06-BDIV-008-01 and ANR-09-BLAN-0145-01). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Contacts:
Arnaud Estoup
NRA UMR Centre de
Biologie et de Gestion des Populations
estoup@supagro.inra.fr

Jen Laloup
Public Library of Science
jlaloup@plos.org
415-624-1220

Citation: Lombaert E, Guillemaud T, Cornuet J-M, Malausa T, Facon B, et al. (2010) Bridgehead Effect in the Worldwide Invasion of the Biocontrol Harlequin Ladybird. PLoS ONE 5(3): e9743. doi:10.1371/journal.pone.0009743

Provided by Public Library of Science

Citation: Bridgehead Effect in the Worldwide Invasion of the Biocontrol Harlequin Ladybird (2010, March 17) retrieved 20 August 2026 from https://sciencex.com/wire-news/30261107/bridgehead-effect-in-the-worldwide-invasion-of-the-biocontrol-ha.html

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