Résumé
Unveiling the genetic basis of local adaptation to environmental variation
is a major goal in molecular ecology. In rugged landscapes characterised
by environmental mosaics, living populations and communities can
experience steep ecological gradients over very short geographical
distances. In lowland tropical forests, interspecific divergence in
edaphic specialization (for seasonally flooded bottomlands and seasonally
dry terra firme soils) has been proven by ecological studies on adaptive
traits. Some species are nevertheless capable of covering the entire span
of the gradient; intraspecific variation for adaptation to contrasting
conditions may explain the distribution of such ecological generalists. We
investigated whether local divergence happens at small spatial scales in
two stands of Eperua falcata (Fabaceae), a widespread tree species of the
Guiana Shield. We investigated SNP and sequence divergence as well as
spatial genetic structure (SGS) at four genes putatively involved in
stress response and three genes with unknown function. Significant genetic
differentiation was observed among sub-populations within stands, and
eight SNP loci showed patterns compatible with disruptive selection. SGS
analysis showed genetic turnover along the gradients at three loci, and at
least one haplotype was found to be in repulsion with one habitat. Taken
together, these results suggest genetic differentiation at small spatial
scale in spite of gene flow. We hypothesize that heterogeneous
environments may cause molecular divergence, possibly associated to local
adaptation in E. falcata.