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Great genetic diversity but high sel¿ng rates and short-distance gene ¿ow characterize populations of a tree (Foetidia; Lecythidaceae) in the fragmented tropical dry forest of the Mascarene islands

Cuenin N., Flores O., Rivière E., Lebreton G., Reynaud B., Martos F.. 2019. In : Flores Olivier (ed.), Ah-Peng Claudine (ed.), Wilding Nicholas (ed.). Book of abstracts talks of of the third international conference on Island ecology, evolution and conservation. Saint-Denis : Université de la Réunion, p. 115-115. International conference on Island ecology, evolution and conservation. 3, 2019-07-08/2019-07-13, Saint-Denis (Réunion).

Following the global trend of deforestation and degradation, tropical dry forests in the Mascarenes archipelago on Reunion has undergone harsh reduction and fragmentation within 3 centuries of human occupation. We investigated the genetic diversity, mating system, and gene ¿ow in fragmented populations of the native tree Foetidia mauritiana (Lecythidaceae) on Reunion, using microsatellite genotyping of adults (in- and ex situ) and seed progenies (in situ only). To test genetic isolation be-tween the Mascarene islands, we also genotyped conspeci¿c adults on Mauritius, and trees of Foetidia rodriguesiana on Rodrigues. We found a high genetic diversity among the trees on Reunion, but no population structure (G'ST: 0.039¿0.090), and an increase of the ¿xation index (FIS) from adults to progenies. A subsequent analysis of mating systems from progeny arrays revealed sel¿ng rates > 50%in fragmented populations and close to 100% in lone trees. A paternity analysis revealed pollen ¿ow ranging from 15.6 to 296.1 m within fragments. At broader scale, the populations of F. mauritiana on Reunion and Mauritius are genetically di¿erentiated. The morphologically allied taxa F. rodriguesiana and F. mauritiana are clearly isolated. Therefore, this case study shows that genetic diversity may persist after deforestation, especially in long-lived tree species, but the reproductive features may be deeply altered during this process. This would explain the low seed production and the absence of recruitment in F. mauritiana. Restoration programs should take into account these features, as well as the importance that trees ex situ represent in restoring and conserving diversity.

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