Landscape Evolution as a Diversification Driver in Freshwater Fishes

Abstract

The exceptional concentration of vertebrate diversity in continental freshwaters has been termed the “freshwater fish paradox,” with > 15,000 fish species representing more than 20% of all vertebrate species compressed into tiny fractions of the Earth’s land surface area (<0.5%) or total aquatic habitat volume (<0.001%). This study asks if the fish species richness of the world’s river basins is explainable in terms of river captures using topographic metrics as proxies. The River Capture Hypothesis posits that drainage-network rearrangements have accelerated biotic diversification through their combined effects on dispersal, speciation, and extinction. Yet rates of river capture are poorly constrained at the basin scale worldwide. Here we assess correlations between fish species density (data for 14,953 obligate freshwater fish species) and basin-wide metrics of landscape evolution (data for 3,119 river basins), including: topography (elevation, average relief, slope, drainage area) and climate (average rainfall and air temperature). We assess the results in the context of both static landscapes (e.g., species-area and habitat heterogeneity relationships) and transient landscapes (e.g., river capture, tectonic activity, landscape disequilibrium). We also relax assumptions of functional neutrality of basins (tropical vs. extratropical, tectonically stable vs. active terrains). We found a disproportionate number of freshwater species in large, lowland river basins of tropical South America, Africa, and Southeast Asia, under predictable conditions of large geographic area, tropical climate, low topographic relief, and high habitat volume (i.e., high rainfall rates). However, our results show that these conditions are only necessary, but not fully sufficient, to explain the basins with the highest diversity. Basins with highest diversity are all located on tectonically stable regions, places where river capture is predicted to be most conducive to the formation of high fish species richness over evolutionary timescales. Our results are consistent with predictions of several landscape evolution models, including the River Capture Hypothesis, Mega Capture Hypothesis, and Intermediate Capture Rate Hypothesis, and support conclusions of numerical modeling studies indicating landscape transience as a mechanistic driver of net diversification in riverine and riparian organisms with widespread continental distributions.

Landscape dynamics and diversification of the megadiverse South American freshwater fish fauna

“…The fish faunal interchange around 30 Ma between these bioregions ( Fig. 4 A ) may have been enhanced by megariver capture events (>10,000 km 2 ) in the sub-Andean foreland in the vicinity of the Bolivian Orocline ( 16 , 28 , 29 ). The abrupt decrease in dispersal between these bioregions coincides temporally with the rise of the Michicola Arch (c. 30 to 23 Ma; Fig.…”

“…In particular, river capture, in which a river drainage system is diverted from its historic bed to a neighboring bed, is a landscape evolution process that exerts a potent influence on diversification in obligate freshwater organisms, because it both severs existing and constructs new corridors of aquatic habitat among portions of adjacent drainage basins ( 18 , 28 ). Because continental fishes are eco-physiologically restricted to freshwater habitats within drainage basins, watersheds represent natural dispersal barriers, as evidenced by the strong spatial concordance of geographic ranges in freshwater fish species with basin boundaries ( 28 , 29 ). By isolating and connecting populations of aquatic taxa across watershed divides, river capture exerts complex effects on the diversity of freshwater organisms, for example by elevating extinction risk through geographic-range contraction, promoting speciation by genetic isolation and vicariance, and increasing biotic homogenization by dispersal and gene flow ( 16 , 30 – 32 ).…”

The role of landscape evolution in the genetic diversification of a stream fish Sarcocheilichthys parvus from Southern China

“…Phylogeographic research on freshwater fish has continued to play an important role in understanding the underlying causal factors shaping inter-and intra-specific genetic variations of freshwater fish biodiversity across contemporary isolated drainages (Shelley et al, 2020;Van Steenberge et al, 2020;Waters et al, 2020;Lima et al, 2021;Yang et al, 2022). Landscape evolution, either through tectonic activities or drainage rearrangements, has been considered to be a major driver for the diversification of obligate freshwater fishes (Burridge, et al, 2006;Unmack et al, 2013;Swartz et al, 2014;Xu et al, 2014;Zúñiga-Vega et al, 2014;Craw et al, 2016;Lima et al, 2017;Souza et al, 2020;Sholihah et al, 2021;Barreto et al, 2022;Souto-Santos et al, 2022;Val et al, 2022). One type of drainage rearrangement is stream capture, a geomorphological process that refers to a stream displacing a portion of another neighboring stream due to tectonic or erosive events (Bishop, 1995).…”

The salmonid and the subsurface: Hillslope storage capacity determines the quality and distribution of fish habitat

“…Geologic history (e.g., Waples et al, 2008), landscape evolution (e.g., Montgomery, 2000) and channel network dynamics (e.g., Stokes & Perron, 2020; Val et al, 2022), and erosional and flood dynamics (Waples et al, 2008), all influence salmon diversity and resilience in the Anthropocene. Here we add another geomorphic component: the CZ.…”