Using the most comprehensive fish occurrence database, we evaluated the importance of ecological and historical drivers in diversity patterns of subdrainage basins across the Amazon system. Linear models reveal the influence of climatic conditions, habitat size and sub-basin isolation on species diversity. Unexpectedly, the species richness model also highlighted a negative upriver-downriver gradient, contrary to predictions of increasing richness at more downriver locations along fluvial gradients. This reverse gradient may be linked to the history of the Amazon drainage network, which, after isolation as western and eastern basins throughout the Miocene, only began flowing eastward 1–9 million years (Ma) ago. Our results suggest that the main center of fish diversity was located westward, with fish dispersal progressing eastward after the basins were united and the Amazon River assumed its modern course toward the Atlantic. This dispersal process seems not yet achieved, suggesting a recent formation of the current Amazon system.
Bibliographical noteFunding Information:
A particular thought to J. Maldonado-Ocampo who recently passed away during a fishing trip in the R?o Vaup?s (Colombia). For comments, we thank R. E. Reis, J. Chave, J. G. Lundberg, C. Th?baut, three anonymous reviewers, and the Science Advances editor S. Naeem. This research benefited from support from the ERANet-LAC (www.eranet-lac.eu/) ?AmazonFish? (ELAC2014/ DCC-0210) project. French Laboratories of Excellence ?CEBA? (ANR-10-LABX-25-01) and ?TULIP? (ANR-10-LABX-41 and ANR-11-IDEX-0002-02) were also acknowledged. J.Z. acknowledged Brazil?s CNPq for a productivity grant (#313183/2014-7). M.S.D. thanked CNPq (150784/2015-5) and FAPDF (#00193.00001819/ 2018-75) for funding. J.S.A. acknowledged support from U.S. NSF awards 0614334, 0741450, and 1354511. B.H. acknowledged support from the EU ERA-NET BiodivERsA project ?Odysseus? 3-2015-26. G.T.-V. received grants from Foundation of Support to Research in the Amazon (PAREV/FAPEAM 019/2010), CAPES (Pro-Amazon Program: Biodiversity and Sustainability, process 6632/14-9), and FAPESP (S?o Paulo Research Foundation #2016/ 07910-0). R.G.F. received a grant from Brazil?s FAPESPA (ICAAF #094/2016). All data were collected through the AmazonFish project (www.amazon-fish.com).
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