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This thesis investigates diversification processes in tropical tree species, using the genus Guibourtia Benn. as a biological model (Leguminosae-Detarioideae). The aim is to understand the historical, biological and environmental mechanisms that account for the diversity of the genus. In particular, this PhD aims to: (1) understand the relative role, at the interspecies level, of neutral and selection forces in the diversification of Guibourtia species, by combining molecular phylogeny with the characterization of functional traits and ecological niches; and (2) at the intra- species level, investigate the causes of population differentiation in three Guibourtia species. At the interspecies level, the molecular phylogeny dating based on whole plastid genome sequencing was congruent with the current taxonomy (the species were generally monophyletic). The dating showed diversification in the Middle Miocene into three clades corresponding to the subgenera Guibourtia , Gorskia and Pseudocopaiva . It also showed that two neo-Tropical species resulted from migration from Africa to South America during the Late Miocene. In considering climate niches, it was also demonstrated that the selection of some morphological traits was convergent within the different clades. This result was confirmed by an ecophysiological experiment, which showed that light was an important factor of selection and adaptive differentiation between three species ( G. ehie , G. coleosperma and G. tessmannii ). At the intraspecies level, a phylogeographic study of two Guibourtia species revealed that biogeographic barriers climatic gradients appear to have contributed to the genetic differentiation of G. ehie and G. coleo- sperma populations respectively. This study also investigates the limits of G. ehie distribution, since its populations showed a strong genetic differentiation between West and Central Africa, associated with diagnostic morphological features. Finally, in G. tessmannii , a species with dehiscent fruits and arillate seeds, we identified the main dispersal species, including hornbills ( Ceratogymna atrata ), that may have contributed to long-distance gene flows influencing the spatial structure of genetic variation among populations. This thesis, using the Guibourtia genus as a biological model, has brought new material to help understand the mechanisms generating diversity in tropical tree species.

Évolution et adaptation fonctionnelle des arbres tropicaux : le cas du genre <I>Guibourtia</I> Benn.