Résumé
Understanding the evolutionary dynamics of genetic diversity is
fundamental for species conservation in the face of climate change,
particularly in hyper-diverse biomes. Species in a region may respond
similarly to climate change, leading to comparable evolutionary dynamics,
or individualistically, resulting in dissimilar patterns. The second
largest expanse of continuous tropical rain forest (TRF) in the world is
found in Central Africa. Here, present-day patterns of genetic structure
are thought to be dictated by repeated expansion and contraction of TRFs
into and out of refugia during Pleistocene climatic fluctuations. This
refugia model implies a common response to past climate change. However,
given the unrivalled diversity of TRFs, species could respond differently
because of distinct environmental requirements or ecological
characteristics. To test this we generated genome-wide sequence data for
>750 individuals of seven co-distributed plants from Lower Guinea
in Central Africa. We inferred species’ evolutionary and demographic
histories within a comparative phylogeographic framework. Levels of
genetic structure varied among species and emerged primarily during the
Pleistocene, but divergence events were rarely concordant. Demographic
trends ranged from repeated contraction and expansion to continuous
growth. Furthermore, patterns in genetic variation were linked to
disparate environmental factors including climate, soil and habitat
stability. Using a strict refugia model to explain past TRF dynamics is
too simplistic. Instead, individualistic evolutionary responses to
Pleistocene climatic fluctuations have shaped patterns in genetic
diversity. Predicting the future dynamics of TRFs under climate change
will be challenging and more emphasis is needed on species ecology to
better conserve TRFs worldwide.