Genotyping by sequencing data of five legume tree species widespread in the rainforests of West and Central Africa

Although today the forest cover is continuous in Central Africa this may
have not always been the case, as the scarce fossil record in this region
suggests that arid conditions might have significantly reduced tree
density during the Ice Ages. Our aim was to investigate whether the dry
ice-age periods left a genetic signature on tree species that can be used
to infer the date of the past fragmentation of the rainforest. We
sequenced reduced representation libraries of 182 samples representing
five widespread Legume trees and seven outgroups. Phylogenetic analyses
identified an early divergent lineage for all species in West Africa
(Upper Guinea), and two clades in Central Africa: Lower Guinea-North and
Lower Guinea-South. As the structure separating the Northern and Southern
clades -congruent across species- cannot be explained by geographic
barriers, we tested other hypotheses with demographic model testing using
∂a∂I. The best estimates indicate that the two clades split between the
Upper Pliocene and the Pleistocene, a date compatible with forest
fragmentation driven by ice-age climatic oscillations. Furthermore, we
found remarkably older split dates for the shade-tolerant tree species
with non-assisted seed dispersal than for light-demanding species with
long-distance wind dispersal. Different recolonisation abilities after
recurrent cycles of forest fragmentation seem to explain why species with
long-distance dispersal show more recent genetic admixture between the two
clades than species with limited seed dispersal. Despite their old
history, our results depict the African rainforests as a dynamic biome
where tree species have expanded relatively recently after the last
glaciation.