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

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Abstract
Landscape features can influence gene flow detected in genetic structure and diversity. The effect will depend on the ability to disperse and may vary between species. Waterfalls and rapids in the Amazon basin have been suggested as causing the diversification and genetic structure of freshwater species, including turtles. Thus, we evaluated the spatial distribution of genetic diversity of Podocnemis unifilis, a widely distributed and endangered turtle, along the main rivers of the Brazilian Amazon. We used the mitochondrial DNA control region to characterize the population structure and test hypotheses of isolation by distance (IBD) or resistance (IBR) through an integrative approach using genetic, geographic, and ecological data. We compared matrices of geographic (linear and in-water distance) and resistance distances (niche modeling and/or waterfalls and rapids) in genetic distance. We found heterogeneous levels of genetic diversity (no spatial patterns) and a geographically complex pattern of population genetic structure. In some localities, gene flow follows watersheds, connecting watercourses, but it also has some genetic structure withing rivers, where waterfalls and rapids act as barriers to dispersal. The IBR better explains the genetic distance, the movement of individuals is influenced by aquatic, vegetational, biological, and geomorphological variables. Efforts for the conservation of the species need to be applied in all its distribution considering landscape genetics. Thus, projects that impact aquatic organisms such as dams and others need to rely on regional or even local migration of Amazonian turtle populations in rivers, verifying the connectivity within each watercourse, improving the knowledge of negative impacts.

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