Abstract
Genetic admixture and plasticity along with propagule pressure, large seed dispersal distances and fast adaptation support successful establishment and spread of introduced species outside their native range. Consequently, introductions may display climatic niche shifts in the introduced range. Douglas-fir, a controversial forest and ornamental conifer represented by two ecologically different and hybridising varieties, was transferred multiple times outside the native range in North America. Here, we compare climatic and genetic patterns of 38 native populations from North America with six old Pseudotsuga menziesii populations with natural regeneration in the introduced range in Central Europe. Following variety and geographic origin assessment of introduced populations, genotypic and climatic data were examined for signatures of inter-varietal gene flow, reduced genetic diversity, presence of fine-scale spatial genetic structure (SGS), dispersal patterns, and climate similarities between native and introduced range. In the introduced range, dominating coastal variety originated from a restricted area in the US, whereas the interior variety, with limited presence in the European sites, displayed wider geographic origin. Variety hybrids with contributing coastal, but not the interior parent were identified. Differences in genetic diversity between both ranges, but also among the parent and their respective offspring populations in Europe were not found. Old populations in general lacked any SGS, whereas natural regeneration revealed different patterns of SGS. Distances of propagule dispersal ranged between 2.5 and 92 m. The climate of the studied European introduced range was most similar to the climate of the coastal variety from the western Cascade range from which the majority of the analysed coastal European Douglas-fir, but not the European interior variety, was assigned to originate. The results we present here shed not only light on dynamics of invasive species in the introduced range in general, but also allow for refinement of climatic niche modeling when using lower than species level.
Highlights
It is more often a rule rather than an exception that non-native species were introduced into new ranges multiple times and/or from different geographic and genetically differentiated source populations allowing for interactions not possible in the native range (e.g. Dlugosch and Parker 2008; Henry et al 2009; Uller and Leimu 2011; Novo et al 2015; Rijal et al 2015)
Individuals assigned to the coastal variety were exclusively associated to the central reference genetic cluster (RGC) (Q = 0.75–0.95) which is situated in OR and WA (Table 2, Fig. 1a)
Individuals assigned to the interior variety, showed genetic signatures of all three reference genetic clusters (RGCs) in the native range and exhibit a broader latitudinal origin
Summary
It is more often a rule rather than an exception that non-native species were introduced into new ranges multiple times and/or from different geographic and genetically differentiated source populations allowing for interactions not possible in the native range (e.g. Dlugosch and Parker 2008; Henry et al 2009; Uller and Leimu 2011; Novo et al 2015; Rijal et al 2015). It is more often a rule rather than an exception that non-native species were introduced into new ranges multiple times and/or from different geographic and genetically differentiated source populations allowing for interactions not possible in the native range As indicated by a number of studies, intraspecific genetic admixture, i.e. blending and interbreeding of native source populations in the new distribution range, contributes significantly to the invasive success of non-native species (reviews of Prentis et al 2008; Rius and Darling 2014). On the long-term the genetic admixture boosts the genetic variation brought by introduction into the non-native range, providing a larger pool of raw material for adaptive evolution (Kolbe et al 2004; Pairon et al 2010; Rius and Darling 2014). We found them in native areas when estimating genetic structure, which allow us to study events such as species demographic history, colonization out of refugia, past and present hybridization events (van Loo et al 2015, van Boheemen et al 2017)
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