Résumé
PREMISE: A good understanding of genetic variation and gene dispersal in
tree populations is crucial for their sustainable management, particularly
in a context of rapid environmental changes. West African Sudanian
savannahs are undergoing fragmentation and degradation, partly due to
expansion of crop cultivation and monocultures that reduce tree density
and may impact pollinators. This could affect the population dynamics of
important indigenous trees. We investigated the influence of habitat
fragmentation on patterns of genetic diversity and gene dispersal of a key
Sudanian agroforestry tree species, Parkia biglobosa. METHODS: Using ten
highly polymorphic nuclear microsatellites, we genotyped 2475 samples from
reproductive trees, seedlings and embryos in four tree populations
presenting different levels of habitat fragmentation. RESULTS: Parkia
biglobosa presented high genetic diversity, similar across the four
populations studied. Genetic diversity and inbreeding were similar between
adults and embryo cohorts. In all four populations the selfing rate was
less than 1%. A high effective number of pollen donors per tree
(NEP~18-22) and a high pollen immigration rate were observed (ranging from
34 to 74%). Pollen dispersal was characterized by a fat-tailed
distribution with mean estimates exceeding 200 m. In three populations,
stem diameter had a pronounced effect on male reproductive success. Here,
the highest male reproductive success was observed in trees with a
diameter at breast height of between 60 and 75 cm. CONCLUSIONS: At the
scale analyzed, fragmentation does not seem to pose limitations to gene
flow in any of the sites investigated, regardless of the landscape
configuration associated with the different tree stands examined. The
study provides useful insights on the reproductive biology of an important
tree species in the West African savannahs.