Investigating population differentiation and local adaptation of a forest tree (Coffea mauritiana) endemic to Reunion Island
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Vendredi 12 juin 2020 à 14h00
Edith GAROT
Postdoctorante à GQE-Le Moulon, Équipe BASE
Invitée par l’UMR à présenter ses travaux de thèse préparée à l’IRD, UMR DIADE, Université de Montpellier
Investigating population differentiation and local adaptation of a forest tree (Coffea mauritiana) endemic to Reunion Island
Résumé
Oceanic islands provide unique systems to uncover ecological and evolutionary processes in species. Geographic isolation in combination with habitat diversity have favored processes of speciation and population divergences, leading to high rates of endemism and patterns of local adaptation. However, isolation also resulted in higher vulnerability to external disturbances, such as global climatic changes. Displaying large environmental gradients at small spatial scale, the recently emerged Reunion Island (about 2 Ma), appears as an exceptional laboratory to support such evolutionary studies. Coffea mauritiana is an endemic tree species from Reunion Island and Mauritius. This coffee tree is widely distributed in Reunion Island and encompasses contrasted environments at small spatial scale. Using genetic approaches, this thesis aimed to: (1) investigate population divergences of a widespread woody species in Reunion Island; (2) assess the impact of past climatic events on the species demography and its potential ecological niche ; (3) identify potential processes of local adaptation to local climatic gradients. Genomic resources were obtained by DArTseq genotyping of 323 trees from 34 localities covering the distribution area of the species. Neutral genomic differentiation was first assessed by estimating genetic diversity, population structure and differentiation. The phylogenic relationships between the inferred population clusters was studied, and the main factors of population differentiation were also identified. Model-free statistical methods were then used to estimate the demographic history of the species. Finally, leaf adaptive traits were investigated in Coffea mauritiana, using a multi-approach analysis combining phenotypic assessment in common garden and transcriptomics. Results from this work improve the current knowledge of Reunion Island endemic species and further the understanding on the genetic basis of local adaptation in reunionese species. This information will provide important guidelines on how to organize forest tree management to face future climatic changes.