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A tiny, three-inch fish might hold the key to unlocking an ancient secret of evolution.
Tucked away in the southern Appalachian Mountains is the Greenfin Darter (Nothonotus chlorobranchius), a hardy fish that exhibits tremendous genetic diversity. Until recently, the driver of this diversity was unknown. Researcher Maya Stokes, along with Yale Professor Thomas Near and a team of dedicated scientists, set out to discover the mechanism behind what appears to be real-time allopatric speciation, or speciation prompted by geographic isolation, in the Appalachian Mountains.
Near puts the overall research question simply. “Why are we seeing species richness within the rivers themselves?” he said. The answer lies in the stones—erosion, to be exact.
The Greenfin Darter is selective of its habitat, preferring hard metamorphic rock over soft sedimentary rock. Erosional processes in the Tennessee River, however, have exposed areas of sedimentary rock, separating regions of metamorphic rock. This has forced Greenfin Darter populations into isolation. The team’s research displays that erosion of metamorphic rock has severely reduced gene flow between populations of N. chlorobranchius, driving genetic divergence up. This research—an intersection between the fields of ichthyology (the study of fishes) and geoscience—has allowed a novel explanation of species divergence in what Near calls “geologically quiet” areas without tectonic influence.
Stokes is thrilled with the recent work. “We tried to quantitatively combine data sets across disciplines,” she said. “We were able to integrate these datasets fairly seamlessly, which allowed us to highlight a novel geologic mechanism.” As research endeavors become increasingly integrative, this study is an inspiring example of interdisciplinary success.