Genomic signatures of ecological divergence between savanna and forest populations of a neotropical tree
André Carneiro Muniz, Renata Santiago de Oliveira Buzatti, José Pires de Lemos-Filho, Myriam Heuertz, Alison Gonçalves Nazareno, Maria Bernadete Lovato- Plant Science
Abstract
Background and Aims
In eastern neotropical South America, the Cerrado, a large savanna vegetation, and the Atlantic Forest harbor high biodiversity levels, and their habitats are rather different from each other. The biomes have intrinsic evolutionary relationships with high lineage exchange that can in part be attributed to a large contact zone between them. The genomic study of ecotypes, i.e., populations adapted to divergent habitats, can be a model to study the genomic signatures of ecological divergence. Here we investigated two ecotypes of the tree Plathymenia reticulata, one from Cerrado and the other from Atlantic Forest which have a hybrid zone in the ecotonal zone of Atlantic Forest/Cerrado.
Methods
The ecotypes were sampled in the two biomes and their ecotone. The evolutionary history of the divergence of the species was analyzed with ddRadSeq. The genetic structure and the genotypic composition of the hybrid zone were determined. Genotype-association analyses were performed and the loci under putative selection and their functions were investigated.
Key Results
High divergence between the two ecotypes was found and only early-generation hybrids were found in the hybrid zone suggesting a partial reproductive barrier. Ancient introgression between the Cerrado and Atlantic Forest was not detected. The soil and climate were associated with genetic divergence in Plathymenia ecotypes and outlier loci associated with stress response, stomatal and root development, and to reproduction were found.
Conclusions
The high genomic, ecological, and morpho-physiological divergence between ecotypes coupled with partial reproductive isolation indicate that the ecotypes represent two species and should be managed as different evolutionary lineages. We advise that the forest species should be reevaluated and restated as vulnerable. Our results bring insights into the genomic mechanisms underlying the diversification of species across savanna and forest habitats and the evolutionary forces acting in the species diversification in the Neotropics.