Contrasted invasion processes imprint the genetic structure of an invasive scale insect across southern Europe

Abstract

Deciphering the colonization processes by which introduced pests invade new areas is essential to limit the risk of further expansion and/or multiple introductions. We here studied the invasion history of the maritime pine bast scale Matsucoccus feytaudi. This host-specific insect does not cause any damage in its native area, but it devastated maritime pine forests of South-Eastern France where it was detected in the 1960s, and since then reached Italy and Corsica. We used population genetic approaches to infer the populations' recent evolutionary history from microsatellite markers and Approximate Bayesian Computation. Consistent with previous mitochondrial data, we showed that the native range is geographically strongly structured, which is probably due to the patchy distribution of the obligate host and the limited dispersal capacity of the scale. Our results show that the invasion history can be described in three successive steps involving different colonization and dispersal processes. During the mid-XXth century, massive introductions occurred from the Landes planted forest to SouthEastern France, probably due to transportation of infested wood material after World War II. Stepping-stone expansion, consistent with natural dispersal, then allowed M. feytaudi to reach the maritime pine forests of Liguria and Tuscany in Italy. The island of Corsica was accidentally colonized in the 1990s, and the most plausible scenario involves the introduction of a limited number of migrants from the forests of South-Eastern France and Liguria, which is consistent with an aerial dispersal due to the dominant winds that blow in spring in this region.

The K = 2 conundrum

“…Such studies can provide insight into patterns of gene flow and demography among “populations” that could not be obtained from observation alone (e.g., Cavender‐Bares et al., ; Cullingham et al., ). The applied value of such information has been demonstrated numerous times, for example, in conservation (Cullingham et al., ; Worth et al., ), pest management (Chapuis et al., ; Kerdelhue, Boivin, & Burban, ), the identification of species boundaries (Hamlin & Arnold, ; Janes, Steane, & Vaillancourt, ) and disease control (Atterby et al., ). In response to the increasing interest in genetic structure, there have been significant efforts to develop more refined methods.…”

Tournament ABC analysis of the western Palaearctic population history of an oak gall wasp, Synergus umbraculus

“…Because it is computationally unwieldy to compare all 148 scenarios in a single set, we used a hierarchical two‐stage “tournament” approach to simplify scenario comparison (Barrès et al., ; Kerdelhué et al., ). We first identified the best‐supported scenario in each of the eight model pools, and then compared pool‐winning scenarios in a further analysis.…”

“…A second round then compares support across the pool‐winning scenarios. Such an approach allows identification of a best overall model, or estimation of shared model parameters from a joint posterior distribution (e.g., see Barrès et al., ; Kerdelhué, Boivin, & Burban, ; Wei et al., ). Here, we use a tournament approach to infer the relationships between putative Western Palaearctic glacial refugia for an oak‐feeding insect, Synergus umbraculus .…”

The contribution of genetics and genomics to understanding the ecology of the mountain pine beetle system

“…Phylogeographic insights provide information on historical demographic and geographic patterns, allowing some evolutionary mechanisms to be inferred. Such studies have been used to identify source populations of invasive species (e.g., Kerdelhué et al 2014), delineate conservation management areas (e.g., Haché et al 2017), and predict range limits (e.g., Winkler et al 2012); however, the application of phylogeographic studies in irruptive forest insect species has been questioned. This is primarily because fundamental niche spaces may be obscured by low within-species signatures of genetic diversity as a result of constant population growth and decline (Godefroid et al 2016).…”