Recent lineage diversification in a venomous snake through dispersal across the Amazon River

Identifying the evolutionary and ecological mechanisms that drive lineage diversification in the species-rich tropics is of broad interest to evolutionary biologists. Here, we use phylogeographical and demographic analyses of genome-scale RADseq data to assess the impact of a large geographical feature, the Amazon River, on lineage formation in a venomous pitviper, Bothrops atrox. We compared genetic differentiation in samples from four sites near Santarem, Brazil, that spanned the Amazon and represented major habitat types. A species delimitation analysis identified each population as a distinct evolutionary lineage while a species tree analysis with populations as taxa revealed a phylogenetic tree consistent with dispersal across the Amazon from north to south. Phylogenetic analyses of mitochondrial DNA variation confirmed this pattern and suggest that all lineages originated during the mid- to late Pleistocene. Historical demographic analyses support a population model of lineage formation through isolation between lineages with low ongoing migration between large populations and reject a model of differentiation through isolation by distance alone. The results provide a rare example of a phylogeographical pattern demonstrating dispersal over evolutionary timescales across a large tropical river and suggest a role for the Amazon River as a driver of in situ divergence both by impeding (but not preventing) gene flow and through parapatric differentiation along an ecological gradient.
Keywords
Amazon River;  ecological gradients;  evolutionary lineages;  historical demography;  phylogeographical dispersal;  RADseq;  riverine barriers;  venomous snakes

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Gibbs H.L, SM, Amazonas DR, Chalkidis H, Salazar-Valenzuela D, Moura-da-Silva AM. Recent lineage diversification in a venomous snake through dispersal across the Amazon River. Biol J Linn Soc Lond. 2018 Mar;123(3):651-65. doi:10.1093/biolinnean/blx158.
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