New Insights into the Phylogeny and Worldwide Dispersion of Two Closely Related Nematode Species, Bursaphelenchus xylophilus and Bursaphelenchus mucronatus

Abstract

The pinewood nematode, Bursaphelenchus xylophilus, is one of the greatest threats to coniferous forests worldwide, causing severe ecological damage and economic loss. The biology of B. xylophilus is similar to that of its closest relative, B. mucronatus, as both species share food resources and insect vectors, and have very similar morphological characteristics, although little pathogenicity to conifers has been associated with B. mucronatus. Using both nuclear and mitochondrial DNA markers, we show that B. xylophilus and B. mucronatus form distinct phylogenetic groups with contrasting phylogeographic patterns. B. xylophilus presents lower levels of intraspecific diversity than B. mucronatus, as expected for a species that evolved relatively recently through geographical or reproductive isolation. Genetic diversity was particularly low in recently colonised areas, such as in southwestern Europe. By contrast, B. mucronatus displays high levels of genetic diversity and two well-differentiated clades in both mitochondrial and nuclear DNA phylogenies. The lack of correlation between genetic and geographic distances in B. mucronatus suggests intense gene flow among distant regions, a phenomenon that may have remained unnoticed due to the reduced pathogenicity of the species. Overall, our findings suggest that B. xylophilus and B. mucronatus have different demographic histories despite their morphological resemblance and ecological overlap. These results suggest that Bursaphelenchus species are a valuable model for understanding the dispersion of invasive species and the risks posed to native biodiversity and ecosystems.

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

“…Another finding in this study was the very low level or even complete absence of genetic diversity in the invaded areas, as observed in previous reports on the same species (Fonseca et al 2012;Pereira et al 2013;Vieira et al 2007;Zhang et al 2008;Zhou et al 2007). However, this finding is remarkable in comparison with other invading species in which a loss of genetic diversity during invasion is not as common as previously expected (Bossdorf et al 2005 for a review in plant invasive species; Roman and Darling 2007 for a review in aquatic invasions).…”

“…Many studies have attempted to establish the origin of invasive outbreaks of PWN in different geographic areas (Cheng et al 2008;Figueiredo et al 2013;Fonseca et al 2012;Metge and Burgermeister 2008;Pereira et al 2013;Tares et al 1992;Valadas et al 2012a, b;Vieira et al 2007;Zhang et al 2008;Zhou et al 2007). An Asian origin for European invasive populations of PWN was thus proposed (Figueiredo et al 2013;Fonseca et al 2012;Metge and Burgermeister 2008;Valadas et al 2012b).…”

The mitochondrial genome of the pinewood nematode (Bursaphelenchus xylophilus) lineage introduced in Europe

“…All attempts to amplify the 3 0 region of the ND4 gene (164 bp) and the large non-coding region (NCR) were unsuccessful, probably due to the presence of a highly ATrich NCR (AT content of 98.7%). The three isolates (GenBank JQ429761, JQ514067 and JQ514068) showed no polymorphisms, in agreement with the genetic homogeneity previously observed in Southwestern Europe (Pereira et al, 2013).…”

“…Total DNA was extracted from each isolate using a standard phenol/chloroform method. A total of 40 PCR primers (available upon request) targeting conserved nematode mtDNA regions were used for amplification, under previously described conditions (Pereira et al, 2013). PCR products were sequenced on an ABI 3130XL Automated Sequencer (Applied Biosystems, Foster City, CA) using a primer-walking strategy.…”

Sequence variability of the MspI satellite DNA family of the pinewood nematode Bursaphelenchus xylophilus at different geographic scales

“…During the last century, this species has been scattered by man to several non-native regions of the world, such as Asia and Europe, associated with trade and global flow of wood products (Evans et al, 1996;Webster, 2004). The current known worldwide distribution of the PWN in non-native areas is broad, including several regions of Asia (China, Japan, Korea and Taiwan) and some localized areas in Europe (Portugal, Madeira island and Spain) (Pereira et al, 2013).…”