Genetic differentiation and phenotypic plasticity in life-history traits between native and introduced populations of invasive maple trees

Genetically based phenotypic differentiation between native and invasive populations of exotic plants has been increasingly documented and commonly invoked to explain the success of some invasive species. Nonetheless, this basic information is lacking for invasive trees although they currently represent a major concern worldwide. Reciprocal common gardens were therefore set up in both native and introduced ranges of two exotic maple trees to assess the contribution of genetic differentiation and phenotypic plasticity to tree invasiveness. Almost 3,000 native and invasive seedlings of Acer negundo and Acer platanoides were planted in Canada and in France and their performances were compared in various life-history traits related to growth, leaf phenology and ecophysiology over 2 and 3 year periods. Invasive populations of A. negundo exhibited strong genetic differentiation in all the traits examined. Compared to their native conspecifics, they grew significantly larger in the introduced range and showed lower survival, reduced maximum assimilation rate and increased leaf area in the two gardens. They also expressed greater plasticity for growth and greater phenological sensitivity to temperature. Native and invasive populations of A. platanoides were plastic across environments but in contrast did not exhibit any genetic differentiation. This cross-continental comparison provides evidence that both genetic differentiation and phenotypic plasticity contribute synergistically to tree invasiveness. The influence of these respective processes depends on stage of invasion and the life-history strategy of each species. Plastic effects are likely more important during colonization and establishment whilst genetic effects may contribute more significantly during the spread of established populations

Adaptive evolution and phenotypic plasticity during naturalization and spread of invasive species: implications for tree invasion biology

Although the genetic aspects of biological invasions are receiving more attention in the scientific literature, analyses of phenotypic plasticity and genotype-by-environment interactions are still seldom considered in tree invasion biology. Previous studies have shown that invasions of tree species can be affected by intraspecific phenotypic plasticity, pre-adaptation, and post-introduction evolution, and we suggest there are opportunities for new developments in this field. Here, we present a description of the use of quantitative and molecular genetics in tree invasion biology, and propose an approach based on common garden experiments, quantitative and molecular genetic methods to investigate the role of adaptive evolution, phenotypic plasticity, and genotype-by-environment interactions in tree invasions, particularly at the infraspecific level. We illustrate the utility of this approach using examples from quantitative genetic studies of Pinus and an example from a classical reciprocal common garden experiment with Acer species. By using this approach, researchers can test hypotheses about the role and strength of genetic and environmental effects on population-level invasiveness and gain insights into evolutionary processes that occur during biological invasions. Moreover, knowledge of phenotypic plasticity and local adaption of tree populations may help researchers improve assessments of invasion risk

Field evidence of colonisation by holm oak, at the northern margin of its distribution range, during the anthropocene period

A major unknown in the context of current climate change is the extent to which populations of slowly migrating species, such as trees, will track shifting climates. Niche modelling generally predicts substantial northward shifts of suitable habitats. There is therefore an urgent need for field-based forest observations to corroborate these extensive model simulations. We used forest inventory data providing presence/absence information from just over a century (1880–2010) for a Mediterranean species (Quercus ilex) in forests located at the northern edge of its distribution. The main goals of the study were (i) to investigate whether this species has actually spread into new areas during the Anthropocene period and (ii) to provide a direct estimation of tree migration rate. We show that Q. ilex has colonised substantial new areas over the last century. However, the maximum rate of colonisation by this species (22 to 57 m/year) was much slower than predicted by the models and necessary to follow changes in habitat suitability since 1880. Our results suggest that the rates of tree dispersion and establishment may also be too low to track shifts in bioclimatic envelopes in the future. The inclusion of contemporary, rather than historical, migration rates into models should improve our understanding of the response of species to climate change