Résumé
Little is empirically known about the contribution of mutations to fitness
in natural environments. However, Fisher's Geometric Model (FGM)
provides a conceptual foundation to consider the influence of the
environment on mutational effects. To quantify mutational properties in
the field, we established eight sets of MA lines (7-10 generations)
derived from eight founders collected from natural populations of
Arabidopsis thaliana from French and Swedish sites, representing the range
margins of the species in Europe. We reciprocally planted the MA lines and
their founders at French and Swedish sites, allowing us to test
predictions of FGM under naturally occurring environmental conditions. The
performance of the MA lines relative to each other and to their respective
founders confirmed some and contradicted other predictions of the FGM: the
contribution of mutation to fitness variance increased when the genotype
was in an environment where its fitness was low, i.e., in the away
environment, but mutations were more likely to be beneficial when the
genotype was in its home environment. Consequently, environmental context
plays a large role in the contribution of mutations to evolutionary
process and local adaptation does not guarantee that a genotype is at or
close to its optimum.