Abstract
AbstractAimThe effects of past climatic shifts remain enigmatic for the Amazon region, especially for islands of savanna within the tropical forest known as “Amazonian savannas” (AS). These disjunct savanna areas share many plant and animal species with the Cerrado biome in central Brazil (the CC), fuelling debate over historical connections. We evaluate hypothesized corridors between the CC and the AS, and specifically investigate whether a history of isolation versus recent connections is supported by genetic tests.LocationCerrado and Amazon biomes.TaxonTwo woody plant species: Byrsonima coccolobifolia and B. crassifolia (Malpighiaceae).MethodsAnalyses of genomic data (SNPs from more than 4,500 loci) in 28 populations, as well as chloroplast DNA (cpDNA), were used to test for parallel geographic structuring between the CC and AS—an expected structure if putative corridors provided regional connections between different areas of the CC and AS, and divergence times between the CC and AS were estimated using a composite‐likelihood method based on the site frequency spectrum.ResultsGenomic data, in contrast with cpDNA, generally show strong, concordant genetic structure between the CC and AS in both species, rather than regional grouping of CC with AS populations. In addition, divergence between the CC and AS predates the Last Glacial Maximum.Main conclusionsOur results suggest the AS have remained relatively isolated from the CC even though the strong structure of genomic variation is not shared by cpDNA. We note that past evidence of putative corridors between the CC and AS based solely on cpDNA should be interpreted cautiously since the lack of structure may reflect limited genetic resolution rather than gene flow. As such, the uniqueness of AS may be more pronounced than previously thought, highlighting the importance of protecting these highly threatened areas.
Highlights
Climate change has induced historical shifts in landscapes, including the fragmentation of once widespread biomes into relatively isolated patches
Measures of genomic diversity were generally similar across populations in both species (Table 1), whereas chloroplast DNA (cpDNA) diversity varied somewhat between taxa and among populations (Table S2.1 in Appendix S2), including the fixation of a single cpDNA haplotype in some populations (Figure 3), which contrasts with genomic diversity estimates
The central Cerrado (CC) populations were genetically differentiated from the Amazonian savannas (AS) populations
Summary
Climate change has induced historical shifts in landscapes, including the fragmentation of once widespread biomes into relatively isolated patches. The persistence of such populations and the evolutionary dynamics shaping their current genetic structure are commonly considered in studies of the Northern hemisphere following the glacial retreat of the Pleistocene (Hewitt, 2004; Knowles & Massatti, 2017; Pielou, 1992). The evolutionary history of many tropical biomes is enigmatic because of sparse palynological or fossil evidence (e.g., Jaramillo et al, 2010) and limited or inconsistent support for a range of different hypotheses regarding the magnitude of climate‐induced distributional shifts
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