Populations genetics and the evolution of herbicide resistance in weeds

De nombreux facteurs, incluant les mutations, la sélection, l'hérédité, le système de reproduction et le flux génique sont importants dans révolution de la résistance aux herbicides chez les mauvaises herbes. Les mutations spontanées seraient la principale source de variation génétique pouvant causer l'évolution de la résistance dans une région géographique où la résistance n'a pas été détectée auparavant. En dépit de la fréquence des mutations qui est probablement très faible, la probabilité qu'apparaisse au moins un mutant résistant dans une population sensible peut être élevée chez les espèces de mauvaises herbes qui ont une fécondité élevée et des populations importantes. Des traitements subséquents répétés, avec des herbicides ayant un même mode d'action, pourraient conduire à l'évolution rapide de populations composées en prédominance d'individus résistants. Les mutations de résistance héritées de façon dominante se propagent significativement plus rapidement que les mutations récessives chez les populations se reproduisant au hasard, mais à peu près au même rythme chez les espèces auto-fertiles. Le flux génique issu de la dispersion du pollen ou des graines des populations de mauvaises herbes résistantes peut procurer une source d'allèles de résistance à des champs sensibles adjacents ou avoisinants. Les modèles mathématiques indiquent que la pression de sélection imposée par un herbicide et la fréquence initiale du phénotype résistant influence très fortement le taux d'évolution de la résistance. Les modèles prédisent que les stratégies les plus efficaces pour gérer la résistance sont de réduire l'intensité de sélection par l'herbicide et de limiter la migration de graines résistantes aux herbicides.Numerous factors, including mutation, selection, inheritance, mating System, and gene flow are important in the evolution of herbicide resistance in weeds. Spontaneous gene mutation is believed to be the main source of genetic variation for resistance evolution in a geographic region in which resistance has not been detected previously. Despite mutation frequencies that are probably very low, the probability of occurrence of at least a single resistant mutant in a susceptible population may be high for weed species with high fecundities and large population sizes. Subsequent repeated treatments with herbicides having the same mode of action could lead to the rapid evolution of predominantly resistant populations. Rare dominantly inherited resistance mutations spread significantly more rapidly than recessive mutations in random mating populations, but at roughly the same rate in highly self-fertilizing species. Gene flow, through the movement of pollen or seed from resistant weed populations, may provide a source of resistance alleles to adjacent or nearby susceptible fields. Mathematical models indicate that the strength of selection imposed by a herbicide and the initial frequency of the resistant phenotype most strongly influence the rate of resistance evolution. The models predict that the most effective strategies to manage resistance are to reduce the intensity of selection by herbicide and to limit the migration of herbicide-resistant seed

A standardized set of metrics to assess and monitor tree invasions

Scientists, managers, and policy-makers need functional and effective metrics to improve our understanding and management of biological invasions. Such metrics would help to assess progress towards management goals, increase compatibility across administrative borders, and facilitate comparisons between invasions. Here we outline key characteristics of tree invasions (status, abundance, spatial extent, and impact), discuss how each of these characteristics changes with time, and examine potential metrics to describe and monitor them. We recommend quantifying tree invasions using six metrics: (a) current status in the region; (b) potential status; (c) the number of foci requiring management; (d) area of occupancy (AOO) (i.e. compressed canopy area or net infestation); (e) extent of occurrence (EOO) (i.e. range size or gross infestation); and (f) observations of current and potential impact. We discuss how each metric can be parameterised (e.g. we include a practical method for classifying the current stage of invasion for trees following Blackburn’s unified framework for biological invasions); their potential management value (e.g. EOO provides an indication of the area over which management is needed); and how they can be used in concert (e.g. combining AOO and EOO can provide insights into invasion dynamics; and we use potential status and threat together to develop a simple risk analysis tool). Based on these metrics, we propose a standardized template for reporting tree invasions that we hope will facilitate cross-species and inter-regional comparisons. While we feel this represents a valuable step towards standardized reporting, there is an urgent need to develop more consistent metrics for impact and threat, and for many specific purposes additional metrics are still needed (e.g. detectability is required to assess the feasibility of eradication)

A conceptual framework for predicting temperate ecosystem sensitivity to human impacts on fire regimes

Aim: The increased incidence of large fires around much of the world in recent decades raises questions about human and non-human drivers of fire and the likelihood of increased fire activity in the future. The purpose of this paper is to outline a conce