Data from: Molecular responses to freshwater limitation in the mangrove tree Avicennia germinans (Acanthaceae)

Environmental variation along the geographical space can shape populations
by natural selection. In the context of global warming and changing
precipitation regimes, it is crucial to understand the role of
environmental heterogeneity in tropical trees adaptation, given their
disproportional contribution to water and carbon biogeochemical cycles.
Here, we investigated how heterogeneity in freshwater availability along
tropical wetlands has influenced molecular variations of the Black
Mangrove (Avicennia germinans). Fifty-seven trees were sampled in seven
sites differing markedly in precipitation regime and riverine freshwater
inputs. Using 2,297 genome-wide single nucleotide polymorphic markers, we
found signatures of natural selection by the association between
variations in allele frequencies and environmental variables, including
the precipitation of the warmest quarter and annual precipitation.
Additionally, we found candidate loci for selection based on statistical
deviations from neutral expectations of interpopulation genetic
differentiation. Most candidate loci within transcribed sequences were
functionally associated with central aspects of drought-tolerance or plant
response to drought. Moreover, our results suggest the occurrence of rapid
evolution of a population, likely in response to sudden and persistent
limitation in plant access to soil water, following a road construction in
1974. Observations supporting rapid evolution included the reduction in
tree size and changes in allele frequencies and in transcripts expression
levels associated with increased drought-tolerance, through accumulation
of osmoprotectants and antioxidants, biosynthesis of plant cuticle,
protection against stress-induced proteins degradation, stomatal closure,
photorespiration and photosynthesis. We describe a major role of spatial
heterogeneity in freshwater availability in the specialization of this
typically tropical tree.