Ectomycorrhizal fungal communities of native and non-native Pinus and Quercus species in a common garden of 35-year-old trees

Non-native tree species have been widely planted or have become naturalized in most forested landscapes. It is not clear if native trees species collectively differ in ectomycorrhizal fungal (EMF) diversity and communities from that of non-native tree species. Alternatively, EMF species community similarity may be more determined by host plant phylogeny than by whether the plant is native or non-native. We examined these unknowns by comparing two genera, native and non-native Quercus robur and Quercus rubra and native and non-native Pinus sylvestris and Pinus nigra in a 35-year-old common garden in Poland. Using molecular and morphological approaches, we identified EMF species from ectomycorrhizal root tips and sporocarps collected in the monoculture tree plots. A total of 69 EMF species were found, with 38 species collected only as sporocarps, 18 only as ectomycorrhizas, and 13 both as ectomycorrhizas and sporocarps. The EMF species observed were all native and commonly associated with a Holarctic range in distribution. We found that native Q. robur had ca. 120% higher total EMF species richness than the non-native Q. rubra, while native P. sylvestris had ca. 25% lower total EMF species richness than non-native P. nigra. Thus, across genera, there was no evidence that native species have higher EMF species diversity than exotic species. In addition, we found a higher similarity in EMF communities between the two Pinus species than between the two Quercus species. These results support the naturalization of non-native trees by means of mutualistic associations with cosmopolitan and novel fungi

Genetic and phenological differentiation between introduced and natural populations of Quercus rubra L

Gene diversity within populations of Q rubra was compared between 23 introduced stands and 9 geographic regions within the natural range for 4 enzymes encoded by 4 polymorphic loci. Gene diversity within populations was, in general, higher in introduced stands than in geographic regions, due to differences in allelic frequency profiles. For 2 loci, there were directional increases of frequencies of rare alleles in introduced stands as compared to geographic regions, whereas the mean number of alleles was lower in the former populations. Similarly, intraspecific variation among 15 introduced stands was compared to geographic variation among 18 origins in the natural range for bud flush and leaf coloration in experimental plantations established in France. There was a clinal latitudinal variation for both phenological traits in the natural range. The introduced populations occupied an intermediate position in the rankings for both phenological traits. A hypothesis of genetic differentiation between introduced and natural populations is proposed in light of the results obtained.Différenciation génétique entre les populations introduites et celles de l'aire naturelle du chêne rouge d'Amérique (Quercus rubra L). La diversité génétique intrapopulation chez Q rubra L a été étudiée dans 23 peuplements introduits et 9 régions géographiques de l'aire naturelle avec l'aide de 4 isozymes contrôlés par 4 locus polymorphes. Cette diversité est plus élevée dans les peuplements introduits, à cause des différences de profils des fréquences alléliques, alors que le nombre moyen d'allèles par population est plus faible en Europe que dans l'aire naturelle. Pour 2 loci, les fréquences d'allèles rares sont systématiquement plus élevées dans les peuplements introduits. De la même manière, la variabilité intraspécifique a été étudiée sur un échantillon de 15 populations introduites et 18 populations de l'aire naturelle pour le débourrement et la coloration automnale des feuilles. Les populations de l'aire naturelle manifestent une variabilité suivant un gradient latitudinal. Les populations de l'aire introduite se singularisent par leur position intermédiaire dans le classement des provenances pour les 2 critères phénologiques. L'hypothèse d'une différenciation génétique entre les populations américaines et européennes est émise à la lumière de ces résultats

Decoupling of differentiation between traits and their underlying genes in response to divergent selection

We dissected the relationship between genetic differentiation (Q(ST)) for a trait and its underlying genes (G(STq), differentiation for a quantitative locus) in an evolutionary context, with the aim of identifying the conditions in which these two measurements are decoupled. We used two parameters (theta(B) and theta(W)) scaling the contributions of inter- and intrapopulation allelic covariation between genes controlling the trait of interest. We monitored the changes in theta(B) and theta(W), Q(ST) and G(STq) over successive generations of divergent and stabilizing selection, in simulations for an outcrossing species with extensive gene flow. The dynamics of these parameters are characterized by two phases. Initially, during the earliest generations, differentiation of the trait increases very rapidly and the principal and immediate driver of Q(ST) is theta(B). During subsequent generations, G(STq) increases steadily and makes an equal contribution to Q(ST). These results show that selection first captures beneficial allelic associations at different loci at different populations, and then targets changes in allelic frequencies. The same patterns are observed when environmental change modifies divergent selection, as shown by the very rapid response of theta(B) to the changes of selection regimes. We compare our results with previous experimental findings and consider their relevance to the detection of molecular signatures of natural selectio