In the late-1970s, a small freshwater fish known as the snail darter made history when its newly acquired status as an endangered species helped to temporarily block construction of the Tellico Dam in Tennessee — a David versus Goliath victory in what was the first legal test of the U.S. Endangered Species Act (ESA).
A new study by Yale researchers shows that the tiny fish, discovered in a lower stretch of the Little Tennessee River in 1973, is not a distinct species at all, meaning it was never endangered.
The researchers, who combined analyses of genetic data and the fish’s physical structures, found that the snail darter is actually a subpopulation of a species known as the stargazing darter, a ray-finned species first described in 1887.
The bottom line here is that we want the science used in defense of conservation to be good science.
The discovery demonstrates the ability of modern analytic techniques to help scientists delineate species and identify those that do face endangerment — information that can support efforts to protect the planet’s biodiversity, said Thomas J. Near, professor of evolutionary biology in Yale’s Faculty of Arts and Sciences and senior author of the study.
“While we’re losing the snail darter as a biological conservation icon, our findings demonstrate the capability of genomics, in addition to studying an organism’s observable features, to accurately delimit species,” said Near, who also is the Bingham Oceanographic Curator of Ichthyology at the Yale Peabody Museum. “Through the combination of these methods, scientists today are more empowered than ever to identify endangered species — discoveries that can help guide future conservation decisions.”
He added: “The bottom line here is that we want the science used in defense of conservation to be good science.”
The study was published Jan. 3 in the journal Current Biology. Its lead author, Ava Ghezelayagh, now a postdoctoral scholar at the University of Chicago, completed her Ph.D. in ecology and evolutionary biology at Yale last academic year.
It was in 1975 that the snail darter was declared an endangered species under the ESA, a federal law enacted in 1973 to determine whether development projects pose a threat to fish, wildlife, and plant species at risk of extinction. At the time, the construction of the Tellico Dam by the Tennessee Valley Authority (TVA) was said to threaten the snail darter’s habitat on the Little Tennessee River. The issue sparked nationwide protests demanding the suspension of the project, which had been underway since 1967 and was nearly finished.
Hiram Hill, a law student at the University of Tennessee, sued to stop the dam’s completion and protect the snail darter. In TVA v. Hill, the U.S. Supreme Court ruled 6-3 that completing the dam would destroy the species’ habitat in violation of the ESA, affirming a lower court’s injunction halting the project. The landmark decision gave teeth to the ESA and helped to shape environmental law for decades to come.
In response to the court’s ruling, Congress attached a rider to a spending bill that exempted the Tellico Dam from the ESA, which then-President Jimmy Carter signed into law in September 1979. The dam was completed shortly thereafter. Subsequent recovery efforts succeeded in expanding snail darter populations throughout the Tennessee River system. The fish was removed from the Federal List of Threatened and Endangered Wildlife in November 2022 and hailed as a conservation success story.
For the new study, the researchers decided to reevaluate the snail darter’s status as a distinct species after genomic analysis suggested there is little genetic divergence between it and the stargazing darter, a species that inhabits western tributaries of the Mississippi River from northern Louisiana to southeastern Missouri, with separate historical populations in the Wabash River in Indiana and Illinois.
While there is no universal agreement on what constitutes a species, the formal description of the snail darter as a distinct species, in 1976, had rested on small differences in physical characteristics from the stargazing darter, including the relative length of paired fins, the robustness of its body, width of dorsal saddles, and a slight disparity in the number of anal-fin rays.
To evaluate genetic differences, the researchers examined the physical traits of dozens of specimens of each species — including some of the original specimens used to describe the snail darter in 1976 — and could not replicate the physical differences cited in the original description. Using the general lineage species concept, which defines species as groups of organisms that share a common ancestry and have evolved separately from other lineages, they concluded that the snail darter and stargazing darter are in fact one species, dramatically lacking the genetic and morphological differences observed in 12 sister species pairs of darters.
“Our approach combines analyses of the physical characteristics and the genetics, which scientists weren’t doing in the 1970s,” Near said. “By combining these approaches, we’re discovering species that are truly imperiled, which helps us better understand where to devote resources to protect biodiversity.”
The study’s co-authors are Julia E. Wood, Oliver D. Orr, and Daemin Kim of Yale; Jeffrey W. Simmons of Signal Mountain, Tennessee; Tsunemi Yamashita of Arkansas Tech University; Matthew R. Thomas of the Kentucky Department of Fish and Wildlife Resources; Rebecca E. Blanton of Austin Peay State University; Daniel J. MacGuigan of the University at Buffalo; Edgar Benavides of Yale and Columbia University; Benjamin P. Keck of the University of Tennessee; and Richard C. Harrington of Yale and the South Carolina Department of Natural Resources.
The research was supported by the National Institutes of Health Predoctoral Training Program in Genetics, the Bingham Oceanographic Fund maintained by the Yale Peabody Museum, Yale University, and the Tennessee Valley Authority.
