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Sci Adv. 2019 Sep 11;5(9):eaav8681. doi: 10.1126/sciadv.aav8681. eCollection 2019 Sep.

Unexpected fish diversity gradients in the Amazon basin.

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UMR EDB (Laboratoire Évolution et Diversité Biologique), CNRS 5174, IRD253, UPS; 118 route de Narbonne, F-31062 Toulouse, France.
Departamento de Ecologia, Universidade de Brasília, Brasilia, DF, Brazil.
University of Louisiana at Lafayette, Lafayette, LA 70504, USA.
Center for Global Change and Earth Observations, Michigan State University, East Lansing, MI 48824, USA.
Museo de Historia Natural Alcide d'Orbigny, Av. Potosí 1458, zona Queru Queru, Cochabamba, Estado Plurinacional de Bolivia.
Department of Freshwater Biology, Royal Belgian Institute of Natural Sciences, Vautierstraat 29, B-1000 Brussels, Belgium.
Department of Biology, University of Ghent, K.L. Ledeganckstraat 35, B-9000 Ghent, Belgium.
Research Institute for Nature and Forrest (INBO), Havenlaan 88 bus 73, 1000 Brussels, Belgium.
Universidade Federal de Minas Gerais (UFMG), Instituto de Ciências Biológicas, Av. Antônio Carlos, 6627 Belo Horizonte, MG, Brazil.
Departamento de Ictiología, Museo de Historia Natural, Universidad Nacional Mayor San Marcos, Lima, Perú.
UMR MARBEC (CNRS, IRD, IFREMER, UM), Université de Montpellier, Montpellier Cedex 5, France.
Unidad de Limnología y Recursos Acuáticos, Universidad Mayor de San Simón, Calle Sucre y Parque La Torre s/n, Cochabamba, Bolivia.
Unidad de Ecología y Sistemática (UNESIS), Laboratorio de Ictiología, Departamento de Biología, Facultad de Ciencias, Pontificia Universidad Javeriana, Bogotá, Colombia.
Departamento de Ictiología, Museo Nacional de Historia Natural, La Paz, Bolivia.
Universidade Federal de São Paulo, Instituto do Mar, Campus Baixada Santista, Rua Doutor Carvalho de Mendonça, 144, Encruzilhada, 11070-100 Santos, SP, Brazil.
Department of Wildlife and Fisheries Sciences, Texas A&M University, College Station, TX 77840, USA.
Instituto Nacional de Pesquisas da Amazônia, Coordenação de Biodiversidade, Avenida André Araújo, 2936, Petrópolis, 69067-375 Manaus, AM, Brazil.


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.

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