Dispersal is a key parameter involved in invasion. Despite the importance of obtaining dispersal distance estimate, measuring it remains a real challenge due to its complexity. Here we used a specific case of biological invasions to characterize dispersal. We used cline* theory in the context of multiple introductions in disconnected areas leading to a secondary contact to estimate the variance of the distances between parents and offsprings. We applied this method to the western corn rootworm (WCR), Diabrotica virgifera virgifera, which is one of the most destructive pests of corn and is invading Europe. The two main European invasive outbreaks of WCR are located in Northern Italy and Central Europe and they came from independent introductions from North America. We demonstrated that a secondary contact occurred between these two expanding outbreaks in Northern Italy. We exploited this ongoing process to infer the dispersal of the WCR by analyzing temporary frequency clines at 13 microsatellite markers. A measure of the clines slope and the linkage disequilibrium between microsatellites at the centre of the contact zone provided two estimates of WCR dispersal distance of about 20 km/generation1/2.
*Cline: a cline can be defined as the gradual variation ofthe measured values of some character (phenotypic, genetic, ecological, behavioral, etc.) along a geographical axis.
- Bermond, G., M. Ciosi, E. Lombaert, A. Blin, M. Boriani, L. Furlan, S. Toepfer, and T. Guillemaud. 2012. Secondary Contact and Admixture between Independently Invading Populations of the Western Corn Rootworm, Diabroticavirgiferavirgifera in Europe.Plos One7, e50129