Simulated climate change provokes rapid genetic change in the Mediterranean shrub Fumana thymifolia

Rapid climate change will impose strong directional selection pressures on natural plant populations. Climate-linked genetic variation in natural populations indicates that an evolutionary response is possible. We investigated such a response by comparing individuals subjected to elevated drought and warming treatments with individuals establishing in an unmanipulated climate within the same population. We report that reduction in seedling establishment in response to climate manipulations is nonrandom and results from the selection pressure imposed by artificially warmed and droughted conditions. When compared against control samples, high single-locus genetic divergence occurred in drought and warming treatment samples, with genetic differentiation up to 37 times higher than background (mean neutral locus) genetic differentiation. These loci violate assumptions of selective neutrality, indicating the signature of natural selection by drought. Our results demonstrate that rapid evolution in response to climate change may be widespread in natural populations, based on genetic variation already present within the population.