Landscape configurations determining the genetic structure of the Yellow-Spotted Amazon River Turtle ( Podocnemis unifilis ) in Brazilian Amazonia

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Abstract
Context: Waterfalls and rapids of Amazon basin have been suggested as causing the speciation and genetic structure of many freshwater species, including turtles. The species behavior affects the way waterfalls and rapids limit gene flow. The Yellow-spotted River Turtle ( Podocnemis unifilis ), a widely distributed and endangered Amazonian turtle, does not show the habit to migrate long distances for breeding or eating, but has a complex geographic pattern of genetic variation. Objectives: Here, we investigate isolation by distance and by resistance of P. unifilis . We analyzed if the species ecological niche and waterfalls explain the genetic distance in Brazilian Amazonia. Methods: We evaluated the P. unifilis spatial distribution of genetic variability and diversity using the control region of mitochondrial DNA. We tested the hypotheses of isolation either by distance and resistance through an integrative approach using genetic, geographic, and ecological data. We created a resistance matrix using species niche modeling. We compared the explanation power of geographical distance (both linear and in-water distance) and resistance distance on genetic distance (ΦST fixation index) using multiple regressions and Mantel tests. Results: We found a high genetic diversity and pattern of genetic structure proved to be geographically complex. The population structure followed some watersheds but also showed structuring within different rivers. We found that landscape resistance better explains genetic distance than linear and in-water distance. Conclusions: The resistance of the landscape influences the displacement of individuals by aquatic, vegetational, biological, and geomorphological variables, and efforts to species conservation need to be applied throughout its distribution considering landscape genetics.

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