landscape evolution and fish biodiversity
Landscapes are the tapestry upon which life evolves. Landscapes dynamically change over geologic time in quantifiable ways and by mechanisms that can be constrained and characterized. Some of the most biodiverse regions of the world exclusively experience past landscape changes and large reorganizations in river networks. Is there a mechanistic link between landscape evolution and biodiversification?
My group investigates if rates of landscape evolution are linked with the rates of macroevolutionary processes such as speciation, extinction, and dispersal. Reorganization of river networks are a prime recipe to modify biodiversity because they shuffle the inhabiting species, thus prompting speciation, dispersal, and extinction. Thus, by constraining the controlling mechanisms of river reorganizations, we can better understand the evolution of life on continents. Currently, we focus in the Amazon region as a natural laboratory, the world's most biodiverse continental biome.
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%). Can the exceptional fish species richness of the world’s river basins be explained in terms of topographic transience and river captures?
Figure 1: Global maps of freshwater fish biodiversity. Source: Val et al. (2022).
Figure 2: Conceptual model linking river capture events and fish speciation. Source: Val et al. (2022).
Figure 3: Hypotheses linking rates of river captures and macroevolutionary processes. Source: Val et al. (2022).
My group investigates this question using global databases of species richness as well as field data from the Amazon region. We've found that species richness and topographic relief are positively correlated in regions where tectonic activity is absent. Assuming that medium to high topographic relief in continent interiors is a proxy for topographic transience, we hypothesize that the positive correlation points to an underlying controls of landscape changes, particularly river captures, on fish speciation and evolution.
River captures are a geomorphic process by which a river captures drainage area from a neighboring basin and with it, the inhabiting biota. By separating once-cohabiting populations, river captures are a recipe for speciation through vicariance and dispersal and, depending on its rates, extinction as well. We hypothesize that there ought to be a rate-dependence between fish speciation and the recurrence frequency of river capture events.
The hypothesis linking life and landscape evolution is inspired in observations from numerical models. In a study spearheaded by Nathan Lyons, we coupled landscape evolution with processes of macroevolution. Nathan Lyon's models show that perturbations of the surface caused by faulting or variable rock types caused local changes in relief and river network shapes that tended to generate higher species richness than landscapes that had no significant perturbations in relief and drainage reorganizations.
• Landscape evolution as a diversification driver in freshwater fishes.
Val, P.; Lyons, N; Gasparini, N; Willenbring, J; Albert, J 2022 Frontiers in Ecology and Evolution, 9, doi: 10.3389/fevo.2021.788328
• Topographic controls on divide migration, stream capture, and diversification of riverine life.
Lyons, N. J.; Val, P.; Albert, J. S.; Willenbring, J. K.; Gasparini, N. M. 2020 Earth Surface Dynamics, doi.org/10.5194/esurf-2019-55
the amazon region as a natural laboratory
Figure 4: Photograph of fish collected in a field campaign in the Guiana Shield. Photo credit: Self.
Amazonia contains widespread topographic disequilibrium forms (see the Amazon landscape evolution page). As the most biodiverse river basin on Earth and housing 10% of Earth’s plant and vertebrate species, Amazonia is a prime natural laboratory to explore how landscape change impacts biodiversity.
As residents of waterways, fish are passively redistributed when there is a change in the connection between rivers. It's like they changed the train track without informing the passengers. Based on macroevolution theories, this is a ready-made recipe for producing new species. The key point is that these changes leave records in the landscapes and in the DNA of the fish. It is these records that we are investigating to verify how important this mechanism is in the Amazon and, consequently, for the evolution of life in general.
In collaboration with with researchers Veral Val, Adalberto Val, and their group at the National Institute for Amazon Research (INPA), in Manaus, we have been studying the Cuieiras basin, near Manaus (AM), as a natural laboratory for a river capture event. Our preliminary studies have shown that fish inhabiting basins that have been split apart by river capture events might have preserved this event in their mitochondrial DNA. The molecular data suggests that these basins once shared the same gene pool but have were separated likely due to a river capture event associated with erosion of a fault scarp in the western margin of the Negro River.
•River reorganization affects populations of dwarf cichlid species (Apistogramma genus) in the lower Negro River, Brazil.
Leitão, CS; Souza, É; Santos, CH; Val, P.; Val, AL; Almeida-Val, VMF. 2021 Frontiers in Ecology and Evolution, 9, doi: 10.3389/fevo.2021.760287
• Development and characterization of microsatellite loci in Amazonian dwarf cichlids Apistogramma spp. (Peciformes: Cichlidae): uncovering geological influence on Amazonian fish population.
Leitão, CS; Santos, CH; Souza, EM; Val, P; Vilarinho, G; Silva, MN; Val, AL; Almeida-Val, VMF; 2017; Journal of Applied Ichthyology 33, 6, 1196-1199, doi: 10.1111/jai.13490
- Ongoing work - Together with collaborators Jane Willenbring, Nicole Gasparini, James Albert and Ying Fan, my group is currently investigating the hypothesis that past changes in the configuration of Amazonian rivers may have been a factory for aquatic species. In a large field campaign in 2019, we collected 1,000+ fish in Eastern Amazonia and are currently extracting DNA data to find if past river reorganization events left a fingerprint in their DNA. This work is done in collaboration with INPA.