Ecological genomics of niche exploitation and individual performance in tropical forest trees ; Genómica ecológica de la explotación de nicho y del rendimiento individual en los árboles forestales tropicales ; Génomique écologique de l’exploitation de niche et de la performance individuelle chez les arbres forestiers tropicaux

Tropical forests are home to the greatest diversity of species in the world. How this diversity evolved has not been fully explained, and its origins are still in debate. Even a single hectare comprises many different genera, with closely related tree species coexisting in sympatry. Due to phylogenetic constraints, they are expected to have similar niches and functional strategies, which raises questions about the mechanisms underlying their local coexistence. These tree species are thought to form a complex made up of species that are morphologically similar or have a significant proportion of genetic variability in common, due to recent common ancestry or hybridisation, and which could be the result of adaptive ecological radiation along environmental gradients. Despite the key role of species complexes in the ecology, diversification and evolution of neotropical forests, the eco-evolutionary forces driving their diversity are still not well understood. We explored intraspecific genetic variability and measured its role in individual tree performance based on their growth, taking into account the effects of an environment that we characterised in detail at both abiotic and biotic levels. By combining forest inventories, topography, leaf functional traits and gene capture data from the permanent research facility at Paracou in French Guiana, we applied population genomics, environmental and genomic association analyses and Bayesian modelling to Symphonia and Eschweilera species complexes. We showed that these complexes cover all the local topography and competition gradients present in the study site, while most of the species making up each complex show marked niche differentiation along these same gradients. More specifically, the decrease in water availability along the topo sequence within these species complexes causes changes in leaf functional traits, from acquisition strategies to conservation strategies, both among and within species. Symphonia species are genetically adapted to the distribution of ...