Abstract
Population genetics have been greatly beneficial to improve knowledge about biological invasions. Model-based genetic inference methods, such as approximate Bayesian computation (ABC), have brought this improvement to a higher level and are now essential tools to decipher the invasion routes of any invasive species. In this paper, we performed ABC analyses to shed light on the pinewood nematode (PWN) worldwide invasion routes and to identify the source of European populations. Originating from North America, this microscopic worm has been invading Asia since 1905 and Europe since 1999, causing tremendous damage on pine forests. Using microsatellite data, we demonstrated the existence of multiple introduction events in Japan (one involving individuals originating from the USA and one involving individuals with an unknown origin) and China (one involving individuals originating from the USA and one involving individuals originating from Japan). We also found that Portuguese samples had an American origin. Although we observed some discrepancies between descriptive genetic methods and the ABC method, which are worth investigating and are discussed here, the ABC approach definitely helped clarify the worldwide history of the PWN invasion.
Highlights
Biological invasions are recognized as one of the main threats to biodiversity (Walker & Steffen, 1997) and are fully integrated in global environmental changes induced by humans (Ricciardi, 2007; Sala et al, 2000; Vitousek, Dantonio, Loope, & Westbrooks, 1996; Wilcove, Rothstein, Dubow, Phillips, & Losos, 1998)
We evaluate the global performance of our approximate Bayesian computation (ABC) Random Forest scenario choice, we computed the prior error rate based on the available out-of-bag simulations
We demonstrated the existence (i) of multiple independent introductions from the native area to Japan and China, and (ii) of a bridgehead population, located in Japan, and which was the secondary source of several populations in Asia and Europe. This inference has not been possible using descriptive population genetics methods performed in a previous study (Mallez et al, 2015)
Summary
Biological invasions are recognized as one of the main threats to biodiversity (Walker & Steffen, 1997) and are fully integrated in global environmental changes induced by humans (Ricciardi, 2007; Sala et al, 2000; Vitousek, Dantonio, Loope, & Westbrooks, 1996; Wilcove, Rothstein, Dubow, Phillips, & Losos, 1998). Various models supposed to explain the data are compared based on the similarity between summary statistics simulated from these models and from prior distributions of historical and genetic parameters on one hand and summary statistics computed from the actual samples on the other hand This tool has helped reconstructing invasion histories of multiple species (Ascunce et al, 2011; Barres et al, 2012; Boissin et al, 2012; Fraimout et al, 2017; Guillemaud et al, 2015; Lombaert et al, 2010a; Miller et al, 2005; Pascual et al, 2007; Rius, Turon, Ordonez, & Pascual, 2012; Sherpa et al, 2019).
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