South American freshwater fish diversity shaped by Andean uplift since the Late Cretaceous

Abstract

South America is home to the highest freshwater fish biodiversity on Earth1,2. The hotspot of species richness is located in the western Amazon Basin, and richness decreases downstream along the Amazon River towards the mouth at the Atlantic coast (Fig. 1b, c)3,4, which contradicts the positive relationship between stream size and biodiversity that is commonly observed in river systems across the world5,6. We investigate the role of river rerouting events caused by Andean mountain building and repeated episodes of flooding in western Amazonia in shaping the modern-day richness pattern of freshwater fishes in South America. To this end, we combine a reconstruction of river networks following Andean surface uplift since 80 million years ago with a mechanistic biological model simulating dispersal, allopatric speciation and extinction over the dynamic landscape of rivers and lakes. We show that the numerous small river rerouting events in western Amazonia resulting from mountain building produced highly dynamic riverine habitats that caused high diversification rates, shaping the exceptional present-day richness of this region. The history of marine incursions and lakes, including the Miocene Pebas megawetland system in western Amazonia, played a secondary role. This study is a major step towards the understanding of the processes involved in the interactions between the solid Earth, landscapes, and life of extraordinary biodiverse South America. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=90 SRC="FIGDIR/small/444133v1_fig1.gif" ALT="Figure 1"> View larger version (35K): org.highwire.dtl.DTLVardef@c4643forg.highwire.dtl.DTLVardef@1916aa5org.highwire.dtl.DTLVardef@1f0900forg.highwire.dtl.DTLVardef@81ea9b_HPS_FORMAT_FIGEXP M_FIG O_FLOATNOFig. 1.C_FLOATNO a, Major rivers and drainage basins of South America. HydroRIVERS data from the HydroSHEDS database17; rivers shown that drain a surface area of >4000 km2. b, Freshwater fish species richness per sub-basin (level 5 HydroBASINS17), reproduced from data from Cassemiro, et al. 4. c and d, Richness versus distance to outlet per sub-basins (as shown in panel b), illustrating the positive relationship (richness decreases towards the mouth of the river) for the Amazon (c), and, for comparison, a negative relationship for the Parana-Paraguay river basin (d). C_FIG