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Julien Bonnier

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Climate change poses threats to biodiversity, particularly in tropical rainforests. How tropical rainforest tree species will respond to climate change is uncertain because their extent of local adaptation, its drivers and genetic basis remain poorly known. Characterizing these and the risks of maladaptation in future climates can inform on possible responses and help design strategies for the conservation. This study focuses on Dicorynia guianensis (Fabaceae), a widespread tree species in French Guiana, known for its sensitivity to drought. We performed genome resequencing on 87 individuals sampled in 11 sites across French Guiana to investigate the genetic structure, diversity, the drivers and the genetic basis of local adaptation. Genetic structure analysis identified three distinct groups: western, inland, and eastern, with similar levels of genetic diversity and distributed in areas with different environmental conditions. Six methods applied to detect genomic signatures of selection revealed region-specific selective sweeps and overlap between SNPs identified through outlier analysis or genome-environment association analyses. The most relevant environmental drivers of selection were potential evapotranspiration of the wettest quarter and precipitation of the coldest quarter, indicating that environmental variables related to high rainfall during the wet season are stronger drivers of local adaptation of D. guianensis than drought. Sites located in inland French Guiana had higher risks of climatic maladaptation than coastal sites. Our results contribute to the understanding of local adaptation and risk of maladaptation in tropical trees. They emphasize the need for area-specific approaches in managing tropical tree under the pressures of climate change.