Numerous freshwater caverns are found beneath the eastern North American surface. These landforms, which are deep, dark and hidden from view, make them difficult to study, as well as difficult to date. Their ages can be determined using the geochronology techniques, but they’re difficult. Biologists discovered an unexpected new way to date the formation of cave systems. A new study published in Molecular Biology and Evolution reveals that the evolution of amblyopsids cavefishes – the eyeless species of fish that live underground – provides valuable insights about the formation of landforms millions and millions years ago. By studying the age at which these cavefishes began to lose their eyelids, scientists can tell when these caves first formed. According to a Yale University Department of Ecology & Evolutionary Biology press release, “the ancient subterranean ecologies of eastern North America present a great challenge to date with traditional geochronological dating techniques. These are not reliable beyond a maximum age of 3 to 5 millions years.” Chase Brownstein is a Yale University student and study author. Inferring the age of cave-adapted lineages can help us determine the minimum cave age.
The cavefish lost their vision, then eyes
Small freshwater fishes called Amblyopsids swim in the dim light of eastern North American caves. Like other underground organisms, cavefish have acquired a few adaptations over the years, such as their lack color and vision. They also lack eyes. Brownstein, along with his colleagues, set out to study morphologically and genetically these eyeless and visionless cavefishes in order to learn more. Their morphological analysis revealed that amblyopsids cavefishes evolved from an ancestor who had acquired adaptations to low-light above the surface. However, their genetic analyses showed something more interesting. The team compared the mutations of 88 genes linked to vision in the genomes of the cavefish to demonstrate that different lineages of cavefish have different genetic combinations that cause their loss of sight. This suggests, according to the team that cavefish lineages colonized different cave systems before evolving their low-light adaptations – their loss of vision and lack of eyes – independently in their respective environments. This analysis allowed Brownstein and his colleagues to date the cave systems that each cavefish colonized by using the genetic mutations which caused the vision loss. Brownstein stated in the press release that “the fishes would not have lost their eyes in daylight.” In this case, the caves are estimated to be over 11 million old.
Evolutionary loss and geologic gain
Brownstein and his colleagues used cavefish genomes to determine how many generations passed since the mutations had occurred in each cavefish species. “19659011” The genetic mutations occurred between 11.3 and 2.25 million in years in the oldest cavefish, Troglichthys roseae () as well as 8.7 to 0.3 in years in other cavefish lines. Four or more amblyopsid lineages gained their mutations within their cave ecosystems. The age of these mutations, which is older than that of the oldest caves, cannot be accurately or consistently dated by the geochronological techniques. This suggests the possibility of using this and other methods to date difficult-to-date caverns. Brownstein, along with his colleagues, added that “an emerging field called geogenomics seeks to test hypothesis about landforms evolution by studying biological diversity recorded in genomic data.” Our results demonstrate the potential for using evolutionary histories in earth science to answer questions.
The sources used for this article are:
Molecular Biology and Evolutionand peer-reviewed articles. Our editors also review the accuracy of our work and ensure that it meets our editorial standards. Check out the following sources for this article.
- Molecular Biology and Evolution.Convergent evolution in Amblyopsid Cavefishes, and the Age of Eastern North American Subterranean ecosystems