Recent Study May have Implications for Invasion-Related Concepts in Evolutionary Theory

18 03 2010
This image is by Bruce Marlin and is courtesy of Wikimedia Commons.  It is licensed under the Creative Commons Attribution-Share Alike 2.5 Generic license.

Harmonia axyridis, also known as the Lady Bug and the Harlequin Ladybird

A recent article in PLoS One hypothesis a “bridgehead” effect in certain, highly successful, invasive species that allow them to use one invasion as a staging ground to mount additional invasions.  Following is the original abstract for the article, along with a link to the entire piece:

Abstract

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).

Read the entire article by following this link:
http://www.plosone.org/article/info:doi/10.1371/journal.pone.0009743

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