Worldwide invasion routes of the pinewood nematode:What can we infer from population genetics analyses?

Abstract

Identifying the invasion routes and deter- mining the origin of new outbreaks of invasive species are of crucial importance if we are to understand the invasion process, improve or establish regulatory measures and, potentially, limit the damage. We focused here on the invasion of Europe by the pinewood nematode (PWN), Bursaphelenchus xylo- philus (Steiner & Buhrer, 1934; Nickle 1970; Nem- atoda: Aphelenchoididae), a major pest of forest ecosystems, native to North America and already invasive in Asia since the beginning of the twentieth century. We evaluated the genetic diversity and structure of worldwide field PWN samples by classical and Bayesian population genetics methods to Electronic supplementary material The online version of this article (doi:10.1007/s10530-014-0788-9) contains supple- mentary material, which is available to authorized users. S. Mallez (&) 􏰤 C. Castagnone 􏰤 P. Castagnone-Sereno 􏰤 T. Guillemaud UMR 1355 Institut Sophia Agrobiotech, INRA, 06903 Sophia Antipolis, France e-mail: mallez.sophie@gmail.com S. Mallez 􏰤 C. Castagnone 􏰤 P. Castagnone-Sereno 􏰤 T. Guillemaud UMR Institut Sophia Agrobiotech, Universite ́ de Nice Sophia Antipolis, 06903 Sophia Antipolis Cedex, France S. Mallez 􏰤 C. Castagnone 􏰤 P. Castagnone-Sereno 􏰤 T. Guillemaud UMR 7254 Institut Sophia Agrobiotech, CNRS, 06903 Sophia Antipolis Cedex, France determine the source of the European invasive pop- ulations and the number of introduction events in Europe. We found (1) a very strong spatial genetic structure in native PWN populations, (2) a very low level of polymorphism in each of the invaded areas and (3) contrasted results concerning the origin of European invasive populations. Our findings provide evidence for: (1) a large effect of genetic drift on the biological cycle of the PWN, due to intense demo- graphic bottlenecks during tree infections, not com- pensated for by effective dispersal of its vector; (2) a single introduction event for each of the invaded areas in Japan and Europe and a small effective size for the introduced populations and (3) a mainland Portuguese origin for PWN populations from Madeira. However, more sophisticated methods of invasion route infer- ence and broader sampling are required to conclu- sively determine the origin of the European outbreak. M. Espada 􏰤 P. Vieira 􏰤 M. Mota NemaLab/ICAAM – Instituto de Cieˆncias Agra ́rias e Ambientais Mediterraˆnicas, Universidade de E ́ vora, Nu ́ cleo da Mitra, Ap. 94, 7002-554 E ́ vora, Portugal J. D. Eisenback Department of Plant Pathology, Physiology, and Weed Science, Virginia Tech, Blacksburg, VA 24061, USA M. Harrell Nebraska Forest Service, University of Nebraska, Lincoln, NE 68583-0815, USA