Genetic differentiation and adaptation of plant populations: how important are related herbivores
Résumé
Plants are sessile and genetic exchange is usually limited to several hundred meters. This immobile character of plants has favoured the selection of different genotypes that are adapted to even small scale differences in environmental conditions. Usually, abiotic conditions such as climate and soil have been studied as drivers of adaptation in plants. However, relatively little is known about the potential contribution of biotic factors, such as herbivores and pathogens.We used the black mustard Brassica nigra as a model system, a widespread annual species of European river valleys and coastal habitats. Brassica nigra is associated with a number of herbivore species and some of them are as widespread as their host. The most common insect species is the aphid Brevicoryne brassicae. We sampled seven plant populations from the French Atlantic coast, the Loire (France) and the Saale valley (Germany), and compared the response to spontaneous aphid colonisation in a common garden. In a reciprocal transplant experiment at a regional scale, the contribution of herbivores to local adaptation of plants was analysed. Finally, we sampled aphids from three plant populations and combined all plant and aphid origins in a greenhouse experiment in order to analyse whether local herbivores perform better on their sympatric hosts or vice versa. The present study provides inside into the evolution of plant – herbivore interactions and their importance for genetic differentiation and local adaptation of plants.