Abstract
Wallace’s (1854) Riverine Barrier hypothesis is one of the earliest explanations for Amazon biotic diversification. Despite the importance of this hypothesis for explaining speciation in some animal groups, it has not been studied extensively for plant species. In this study we use a prominent Amazon tree, Buchenavia oxycarpa (Mart.) Eichler (Combretaceae), to evaluate Wallace’s hypothesis along the Rio Negro, a major Amazon tributary that has driven allopatric speciation for several animal taxa. We sampled six individuals from sixteen localities along both river banks, and used a modified ddRADseq protocol to identify SNP markers. Our population genomic data revealed strong genetic structure for B. oxycarpa sampled across banks of the Rio Negro (ϕCT = 0.576, P < 0.001), supporting the hypothesis that the Rio Negro acted as a significant genetic barrier for B. oxycarpa. Our study shows that gene flow for this large and well-dispersed Amazon tree is impeded by riverine barriers, though this has not yet resulted in speciation. Future studies focused on species with different life histories, including species restricted to non-flooded forests, are needed to further advance our understanding of Amazon rivers as drivers of biotic diversification.
Highlights
The patterns of population structure can provide insights into the evolutionary history of individual taxa
Even though no genetic information is available for B. oxycarpa, we would expect high rates of gene flow between populations of this animal-dispersed plant species based on genetic studies of tree species with similar ecology[17,18,19,21]
Populations of B. oxycarpa located on opposite margins of the Rio Negro – a putative riverine barrier – should present weak population genetic structure
Summary
The patterns of population structure can provide insights into the evolutionary history of individual taxa. Ecological differences among species explains much of the interspecific variance in levels of genetic differentiation in birds across physical barriers[6] These findings were observed for other animal species[7,8,9,10]. Even though no genetic information is available for B. oxycarpa, we would expect high rates of gene flow between populations of this animal-dispersed plant species based on genetic studies of tree species with similar ecology[17,18,19,21]. Populations of B. oxycarpa located on opposite margins of the Rio Negro – a putative riverine barrier – should present weak population genetic structure This picture may be expected since results from recent studies have indicated that long-dispersal syndromes, such as vertebrate-dispersal, are responsible for low levels of genetic differentiation for riverine plant species with widespread distributions[17]
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