Phylogenomic data reveal how a climatic inversion and glacial refugia shape patterns of diversity in an African rain forest tree species

The world9s second largest expanse of tropical rain forest is in Central Africa and contains incredible species diversity. Population genetic studies have consistently revealed significant structure across central African rain forest plants, in particular a North-South genetic discontinuity close to the equator at the level of a climatic inversion. Here, we take a phylogeographic approach using 351 nuclear markers in 112 individuals across the distribution of the African rain forest tree species Annickia affinis (Annonaceae). We show for the first time that the North-South divide is the result of a single major colonisation event across the climatic inversion from an ancestral population located in Gabon. We suggest that environmental differences across the inversion and associated trait divergence may have contributed to this phylogenetic discontinuity. We find evidence for inland dispersal, predominantly in northern areas, and variable demographic histories among genetic clusters, indicating that populations responded differently to past climate change. We show how newly-developed genomic tools can provide invaluable insights into our understanding of tropical rain forest evolutionary dynamics.