Back to America: tracking the origin of European introduced populations ofQuercus rubraL.

Abstract

Quercus rubra has been introduced in Europe since the end of the 17th century. It is widely distributed today across this continent and considered invasive in some countries. Here, we investigated the distribution of genetic diversity of both native and introduced populations with the aim of tracing the origin of introduced populations. A large sampling of 883 individuals from 73 native and 38 European locations were genotyped at 69 SNPs. In the natural range, we found a continuous geographic gradient of variation with a predominant latitudinal component. We explored the existence of ancestral populations by performing Bayesian clustering analysis and found support for two or three ancestral genetic clusters. Approximate Bayesian Computations analyses based on these two or three clusters support recent extensive secondary contacts between them, suggesting that present-day continuous genetic variation resulted from recent admixture. In the introduced range, one main genetic cluster was not recovered in Europe, suggesting that source populations were preferentially located in the northern part of the natural distribution. However, our results cannot refute the introduction of populations from the southern states that did not survive in Europe.

Oaks: an evolutionary success story

“…At the same time, a range‐wide common garden of plants from introduced and native populations was established in Europe, and studies of this common garden showed that the introduced populations had diverged from the native gene pool in phenological and growth traits (Daubree & Kremer, ; Merceron, ). As there is evidence to suggest that founder effects were limited (Merceron et al , ), the observed divergence between the two gene pools probably results from selection, due to the difference in environment between the two continents and the particular colonization dynamics of an exotic species (Fig. ).…”

“…Northern red oak, Q. rubra , was introduced into Europe in the eighteenth century and is now widely used in operational forestry across the continent. A genetic survey conducted in Europe and throughout the natural range of this species showed that a diverse germplasm had been introduced, probably from the northern part of the natural distribution (Merceron et al , ). At the same time, a range‐wide common garden of plants from introduced and native populations was established in Europe, and studies of this common garden showed that the introduced populations had diverged from the native gene pool in phenological and growth traits (Daubree & Kremer, ; Merceron, ).…”

A few north Appalachian populations are the source of European black locust

“…According to these authors, one factor contributing to this pattern is that invasive animal populations are often founded by single introduction events, whereas multiple introductions associated with admixture are more common for plants (Uller & Leimu, 2011 (Yang et al, 2017). Studies on invasive trees are less numerous, but they have generally concluded that multiple introductions occurred (Besnard et al, 2014;Merceron et al, 2017;Pairon et al, 2010;Thompson et al, 2015) without being able to clearly identify the population sources. A recent study on the genetic structure of invasive populations of Acacia saligna within several invasive ranges suggested that multiple introductions occurred from populations distributed throughout the Australian native range (Thompson et al, 2015).…”

Oak symbolism in the light of genomics

“…() have shown that the intensity of interspecific gene flow between divergent oak populations or species may have varied over time, with the advance and retreat of glaciation (e.g. Leroy et al ., , ; Merceron et al ., ). Genetic inferences and genome scans for differentiation have suggested that gene flow is heterogeneous over time, space, and genomic regions (Lang et al ., ; Leroy et al ., , ).…”