Diversificação em formações xeromórficas da Mata Atlântica - um estudo de caso com espécies do gênero Pilosocereus Byles & Rowley (Cactaceae)

Abstract

The Brazilian Atlantic Forest (BAF) is considered one of the five main hotspots on the planet. It extends in coastal regions of eastern Brazil, Paraguay and Argentina, displaying a sizeable geographic extension and a wide gradient of altitude, latitude, and climate conditions. Although BAF landscapes are predominantly composed of evergreen rainforests, there are also areas with xerophytic or open shrubby vegetation in the sandy coastal plains and rocky outcrops. These abiotic features promote a considerable heterogeneity of habitats in the BAF, allowing the formation of different physiognomies and plant communities. Most of the hypotheses proposed to explain the origins of the high diversity and endemism in this area are based on allopatric speciation models, such as those built on Pleistocene Refuge Hypothesis (PRH) and riverine hypothesis. Here, we employed molecular data, species distribution modeling (SDM), and tests of niche equivalency and similarity (NES) using Pilosocereus arrabidae complex (P. arrabidae, P. ulei, P. brasiliensis subsp. brasiliensis, and P. brasiliensis subsp. ruschianus) as a biological model to address questions related to evolutionary history, dispersal barriers, and refuges of the dry areas within the BAF. We sequenced four molecular markers (1,514 bp) for 97 individuals. However, we failed to solve the shallow relationships between species and individuals, as well as to conduct population genetic analyses, due to the high level of saturation among the aligned loci. The NES and SDM analyses showed distinct niches for the P. brasiliensis subsp., despite the presence of a contact area between Rio de Janeiro and Espírito Santos states, while P. arrabidae and P. ulei displayed low niche overlap during the last 130 ka. The climatic oscillation events imposed a central-south distribution to this species in the present time. Here, we also observed a break in the region of Jequitinhonha and Contas river basins, a region that may work as an ecological barrier, affecting the species distribution. Overall, the P. arrabidae complex seems to be an important biological model for understanding the demography and diversification of taxa from dry areas of the BAF. The prospecting and use of Next Generation Sequencing (NGS) approaches, may be a promising strategy to evaluate biogeographic hypotheses in this study model.