Wet Season Environments Drive Local Adaptation in the Timber Tree Dicorynia guianensis in French Guiana.

The vast tropical rainforests of the Guiana Shield in Northern South America play a vital role in maintaining the region's ecological balance and economy. Increasing pressure from selective logging, gold mining and climate variability threatens these ecosystems. Sustainable rainforest management requires understanding the genetic diversity and local adaptation of key tree species to inform conservation. This study focuses on Dicorynia guianensis (Fabaceae), a widespread and economically important tree species in French Guiana. We performed genome resequencing on 87 individuals sampled in 11 sites across French Guiana to investigate the genetic structure, diversity and genetic basis of local adaptation. Genetic structure analysis identified three distinct groups: western, central and eastern, with similar levels of genetic diversity distributed in areas with different environmental conditions. Six methods applied to detect genomic signatures of selection revealed region-specific selective sweeps and a weak overlap between single nucleotide polymorphisms (SNPs) identified through outlier analysis or genome-environment association analyses. The strongest associations between environmental variables and genomic constitution were observed for potential evapotranspiration of the wettest quarter and for precipitation of the coldest quarter, suggesting that environmental variables related to high rainfall during the wet season are stronger drivers of local adaptation of D. guianensis populations than drought. Sites located in central and western French Guiana had higher risks of climatic maladaptation. These findings advance our understanding of local adaptation and climatic vulnerability in tropical trees and emphasise the need for targeted, area-specific management strategies for conservation and sustainable timber extraction under climate change.