Abstract
The evolutionary processes underlying the high diversity and endemism in the Cerrado, the most extensive Neotropical savanna, remain unclear, including the factors promoting the presence and evolution of savanna enclaves in the Amazon forest. In this study, we investigated the effects of past climate changes on genetic diversity, dynamics of species range and the historical connections between the savanna enclaves and Cerrado core for Qualea grandiflora, a tree species widely distributed in the biome. Totally, 40 populations distributed in the Cerrado core and Amazon savannas were analyzed using chloroplast and nuclear DNA sequences. We used phylogeographic, coalescent and ecological niche modeling approaches. Genetic data revealed a phylogeographic structure shaped by Pleistocene climatic oscillations. An eastern-western split in the Cerrado core was observed. The central portion of the Cerrado core harbored most of the sampled diversity for cpDNA. Ecological niche models predicted the presence of a large historical refuge in this region and multiple small refuges in peripheral areas. Relaxed Random Walk (RRW) models indicated the ancestral population in the north-western border of the central portion of the Cerrado core and cyclical dynamics of colonization related to Pleistocene climatic oscillations. Central and western ancient connections between Cerrado core and Amazonian savannas were observed. No evidence of connections among the Amazonian savannas was detected. Our study highlights the importance of Pleistocene climatic oscillations for structuring the genetic diversity of Q. grandiflora and complex evolutionary history of ecotonal areas in the Cerrado. Our results do not support the recent replacement of a large area in the Amazon forest by savanna vegetation. The Amazonian savannas appear to be fragmented and isolated from each other, evolving independently a long ago.
Highlights
Evolutionary processes outlining the distribution of biodiversity in South American biomes are still poorly understood, especially in the Cerrado, the most extensive Neotropical savanna, extending from 3◦N to 24◦S and from sea level to 1,800 m and occupying approximately 2,000,000 km2 (Ratter et al, 1997; Pennington et al, 2006)
The central portion of the Cerrado core harbors most of the sampled diversity for chloroplast DNA (cpDNA) (Figure 1A) and populations cPIR, cNIQ and cBGA, located in this area, had the highest genetic diversity indices (Table 1)
Our study on the most common and frequent tree species in the Cerrado, Q. grandiflora, indicated a phylogeographic structure shaped by climatic oscillations in the Pleistocene
Summary
Evolutionary processes outlining the distribution of biodiversity in South American biomes are still poorly understood, especially in the Cerrado, the most extensive Neotropical savanna, extending from 3◦N to 24◦S and from sea level to 1,800 m and occupying approximately 2,000,000 km (Ratter et al, 1997; Pennington et al, 2006). Palynological evidence indicates that during the glacial periods, with cooler and drier climate, savannas expanded in the east toward the Atlantic Ocean, and in the north toward the equator, while their southern portion was replaced by subtropical grasslands (Behling and Lichte, 1997; Behling, 1998). Another evidence supporting the larger extension of the Cerrado during the Quaternary Period is the presence of savanna patches within the Amazon forest (Behling, 1998; Ratter et al, 2003)
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