River basins are dynamic environments that are always changing and reorganizing under geologic forces. New research investigates how this shape shifting influences aquatic speciation and extinction.
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The evolution of organisms and of their environments is inherently linked. Although the understanding that the gene pool is dynamic has shaped much of our understanding of modern biology, it’s easy to forget that environments are also in flux.
Research has shown that geologically active areas of the planet, especially those with rugged topography, may generate more species diversity. Stokes and Perron investigate the consequences of changes in topography for aquatic organisms and their habitats.
Drainage basins and river paths are constantly changing because of myriad natural phenomena, including tectonic activity, erosion, damming, and glacier retreat. These processes sometimes lead to abrupt alterations of river paths known as river captures. In the new study, the authors create and combine two models—one that describes macroevolutionary processes of speciation, extinction, and dispersal, and another that simulates river basin changes over time—to investigate how river capture influences the evolution of aquatic organisms.
The results indicate that river capture leads to transient increases in species richness: When the path of a river changes, organisms in the captured regions are introduced into new drainage basins and may become genetically isolated from populations with which they previously could have bred. Over time, these separated populations may diverge sufficiently to become new species.
The authors’ model also shows that both speciation and extinction events are more likely in river basins undergoing reorganization but that the speciation rate often outpaces the extinction rate, leading to higher diversification overall. When river capture events are frequent and organisms typically disperse and speciate slowly, biodiversity increases. Conversely, in cases where a drainage divide is changing but river capture rates are low, biodiversity drops. (Journal of Geophysical Research: Earth Surface, https://doi.org/10.1029/2020JF005652, 2020)
—David Shultz, Science Writer