Evolutionary mechanisms in colonizing plant populations

In a rapidly changing world, human activities offer opportunities for many plant species to colonize new areas. Increasingly, it is recognized that colonization can be accompanied by different ecological and evolutionary processes, acting over relatively short periods of time. When populations colonize novel environments, individuals’ phenotypes will depend on a combination of different, non-exclusive processes, including phenotypic plasticity (PP), local adaptation (LA), environmental maternal effects (EME) and genetic drift (GD)(Monty and Mahy 2009b). Despite these processes have long been studied independently, few attempts have been made to simultaneously address the importance of those processes in plant colonization. Here, we present a set of related studies aiming at disentangling the role of PP, LA, EME and GD in Senecio inaequidens (Asteraceae) in southern France, where it was introduced at a single wool-processing site in the late 19th century. We used seeds from populations growing in contrasted climates to explore the phenotypic variation related to climate. We performed several common garden experiments (Monty et al. 2009, Monty and Mahy 2009a, 2010), as well as a reciprocal sowing experiment with gardens under Mediterranean and Pyrenean climates (Monty et al. in revision). We analyzed climatic phenotypic variation in germination, growth, reproduction, leaf physiology and survival. We characterized genetic structure in the studied populations using AFLP. We found consistent genetic differentiation in growth traits but no home-site advantage, thus weak support for LA to climatic conditions. In contrast, genetic differentiation showed a relationship to colonization history. PP in response to climate was observed for most traits, and it played a particularly important role in leaf trait variation. EME mediated by seed mass influenced all but leaf traits under harsh climate. Heavier, earlier-germinating seeds produced larger individuals that eventually produced more flower heads throughout the growing season. However in a milder climate, EME were negligible. Our different studies suggest that phenotypic variation in response to climate depends on various ecological and evolutionary processes associated with geographical zone and life history traits. Therefore, we argue that a “local adaptation vs. phenotypic plasticity” approach, as often considered in the literature, is not sufficient to fully understand what shapes phenotypic variation and genetic architecture of colonizing populations. References Monty, A., J.-P. Bizoux, J. Escarré, and G. Mahy. in revision. Rapid plant invasion in distinct climates involves different sources of phenotypic variation. PLoS ONE. submitted Monty, A., J. Lebeau, P. Meerts, and G. Mahy. 2009. An explicit test for the contribution of environmental maternal effects to rapid clinal differentiation in an invasive plant. Journal of Evolutionary Biology 22:917-926. Monty, A. and G. Mahy. 2009a. Clinal differentiation during invasion: Senecio inaequidens along altitudinal gradients in Europe. Oecologia 159:305-315. Monty, A. and G. Mahy. 2009b. Évolution des traits d’histoire de vie lors des invasions végétales. Biotechnologie, Agronomie, Société et Environnement 13:449-458. Monty, A. and G. Mahy. 2010. Evolution of dispersal traits along an invasion route in the wind-dispersed Senecio inaequidens (Asteraceae). Oikos 119:1563-1570

Vegetative Regeneration Capacities of Five Ornamental Plant Invaders After Shredding

peer reviewedVegetation management often involves shredding to dispose of cut plant material or to destroy the vegetation itself. In the case of invasive plants, this can represent an environmental risk if the shredded material exhibits vegetative regeneration capacities. We tested the effect of shredding on aboveground and below-ground vegetative material of five ornamental widespread invaders in Western Europe that are likely to be managed by cutting and shredding techniques: Buddleja davidii (butterfly bush, Scrophulariaceae), Fallopia japonica (Japanese knotweed, Polygonaceae), Spiraea x billardii He´rincq (Billard’s bridewort, Rosaceae), Solidago gigantea (giant goldenrod, Asteraceae), and Rhus typhina L. (staghorn sumac, Anacardiaceae). We looked at signs of vegetative regeneration and biomass production, and analyzed the data with respect to the season of plant cutting (spring vs summer), the type of plant material (aboveground vs below-ground), and the shredding treatment (shredded vs control). All species were capable of vegetative regeneration, especially the belowground material. We found differences among species, but the regeneration potential was generally still present after shredding despite a reduction of growth rates. Although it should not be excluded in all cases (e.g., destruction of giant goldenrod and staghorn sumac aboveground material), the use of a shredder to destroy woody alien plant material cannot be considered as a general management option without significant environmental risk

Effectiveness of techniques used to control the development of five invasive amphibious plant species: Crassula helmsii , Hydrocotyle ranunculoides , Ludwigia grandiflora , Ludwigia peploides and Myriophyllum aquaticum . A review.

Parmi les espèces invasives connaissant une expansion rapide en Europe, les plantes dites « amphibies » sont particulièrement problématiques. Elles sont capables de former des populations très denses à la surface des plans d’eau, se développant à la fois sous l’eau et hors de l’eau. La lutte contre ces espèces, en vue de l’éradication totale ou du ralentissement de l’invasion, représente un défi de taille pour les gestionnaires. Une synthèse bibliographique des méthodes de lutte existantes pour Crassula helmsii, Hydrocotyle ranunculoides, Ludwigia grandiflora, L. peploides et Myriophyllum aquaticum a été réalisée, prenant en considération leur efficacité et leur coût. Des 88 études analysées, il ressort une grande disparité d’effort de recherche (nombre d’études, échelles spatiales des études) entre méthodes de lutte et entre espèces. Néanmoins, l’efficacité des différentes méthodes de lutte est comparable pour les cinq espèces étudiées. Globalement, les cas d’éradication sont rares. Ils sont le résultat de luttes mécaniques ou chimiques, souvent couplées à des interventions complémentaires telles que la finition manuelle. Malgré une forte occurrence dans la littérature, la lutte chimique, moins fastidieuse à mettre en place et moins coûteuse que les autres méthodes, n’a montré des niveaux d’efficacité satisfaisants qu’avec certaines matières actives. De même, la lutte biologique a montré peu de résultats encourageants à ce jour. Il est à noter que certains agents de lutte biologique sont d’ores et déjà considérés comme des espèces invasives en Europe. A contrario, malgré leur faible occurrence dans la littérature, l’arrachage manuel ou mécanique suivi de finitions manuelles a donné des niveaux d’efficacité satisfaisants. Vu les difficultés de lutter contre les espèces invasives amphibies et les dommages collatéraux potentiels sur les écosystèmes, un débat impliquant scientifiques, autorités et gestionnaires de plans d’eau devra avoir lieu afin de poser les bases d’une gestion cohérente à grande échelle