Signatures of local adaptation to climate in natural populations of sweet chestnut (Castanea sativa Mill.) from southern Europe

Key message Understanding the adaptive mechanisms of forest species is vital to ensure their survival in a climate change scenario. This study aimed at uncovering the relationship between genetic variability and environmental variables in natural Castanea sativa populations, unveiling how different climate scenarios drove local adaption processes using a landscape genomics approach. Our findings provide useful data for future management of this species. o Context Temperate forest species, such as chestnut (Castanea sativa Mill.), are currently threatened by increasing temperature together with disruption and reduction of precipitation due to climate change. In this context, understanding the adaptation processes of species will help to manage and ensure the conservation of forests. o Aims We studied the relationship between genetic variability and climate variables in natural populations of C. sativa using a landscape genomics approach aimed to identify local adaption processes. o Methods Using five genomic SSRs and eight functional EST-SSRs markers, 268 individuals belonging to ten different natural European chestnut populations distributed in contrasting climatic sites were genotyped. In addition, associations between allelic variation and climatic variables (environmental association analyses approach) were performed using Sam?ada and LFMM. o Results Results highlighted a strong inter-relationship between climate variables and evolutionary processes resulting in adaptive variation. STRU CTU RE analysis based on functional markers split the populations in three separate gene pools (K = 3), mostly in agreement with the different climatic conditions existing in the studied areas. Divergent spatial patterns of genetic variation between rainy and arid areas were found. We detected a total of 202 associations with climate among 22 different alleles, 9% of which related with the outlier locus FIR059, known to be implicated in regulatory mechanisms during water stress adaptation processes. o Conclusion Landscape genomics analyses revealed a pattern of adaptive variation, where specific climatic variables influenced the frequencies distribution and fixation of several alleles, resulting in local adaptation processes of the populations in the investigated areas. Our findings underline the close inter-relationship existing between climate and genetic variability and indicate how this approach could provide valuable information for the management of forest species in a rapidly changing environment.