What was old is new again: thermal adaptation within clonal lineages during range expansion in a fungal pathogen

Range-expanding species are expected to gain an increasing importance in the context of global change. They provide a great opportunity to study contemporary evolutionary changes and to unravel the mechanisms of evolution. Cryphonectria parasitica, the causal agent of chestnut blight, originating from Asia, has been spread since the beginning of the 20th century into different continents. We took advantage of the C. parasitica recent emergence in northern France to study the changes in population genetic structure and in phenotypic traits along this colonization and climatic gradient. Four hundred twenty-seven C. parasitica isolates were sampled in 47 chestnut sites in northern France. The C. parasitica outbreak in the north was found to be due to the expansion of five dominant clonal groups from southern France and to the emergence of a few rare recombined genotypes. The evolutionary changes during C. parasitica range expansion were studied by analyzing phenotypic changes in isolates f...