In watery underground caverns there are strange creatures that live in an eternal midnight. Over generations, these animals have adapted to their isolated and unique environment, and scientists believe their pasty skin and sightless eyes may hold secrets about evolution – and about genetic adaptations that could reveal information about life. longevity, survival from starvation and eye disease. humans.
“These caves are isolated worlds,” said Professor Peter Trontelj, a zoologist at the University of Ljubljana in Slovenia. “If you go down a few meters (below the surface), you enter a new world with totally different ecological conditions.”
Some animals are able to adapt to these dark habitats where no plants grow, making lightless caves, such as those found in Slovenia, natural laboratories for evolutionary biology.
Trontelj directs the GENEVOLCAV project, which studies the European olm. These unusual cave salamanders look like ghostly little swimming snakes with four spindly legs and a crocodile-like snout. Long ago, the ancestors of the olm lived above ground, but once stuck in these caves, they underwent dramatic physical changes to cope with their new surroundings. The olm is not the only creature capable of evolving in this way.
Historically, evolutionary biologists believed that if we were to go back in time and replay the evolutionary timeline, we could just as likely take different evolutionary paths and the world and the creatures within it would look completely different. But the caves show us that this is not the case. Animal adaptations to light- and nutrient-poor environments, such as underground caves, are “generally quite predictable,” Trontelj said. “We now know that every time it will be the same.”
Trontelj and his colleagues showed that this is true within European olmes, which are found in Central and Southeastern Europe. GENEVOLCAV has revolutionized our understanding of these rare cave salamanders. Instead of a single species, as previously thought, they discovered nine potentially different species of olm, each of which developed similar characteristics independently in the eternal watery darkness.
“If you go down a few meters (below the surface), you enter a new world with totally different ecological conditions.”
— Professor Peter Trontelj, coordinator of the GENEVOLCAV project
While all have the same bleached skin, sightless eyes, and elongated snouts, these species are descended from different individual ancestors who found their way into these midnight caves. “Everything happened independently, but more or less parallel,” Trontelj said.
The project aims to assemble the olm genome, which is about 16 times larger than the human genome, and identify the genetic changes that allowed olms to adapt to their unique environments.
“The (physical) changes are the same or very similar, but the question is, ‘Are they caused by the same genes (and) are they the same mutations?’ asked Trontelj. To answer these questions, he and his colleagues dive into the dark depths of the subsoil, sometimes descending into pits 400 meters deep, to measure olms and dab their skin to collect DNA. They will need hundreds of samples to investigate these questions, which could have important implications for human medicine.
“There are several traits of (olms) that are interesting from a broader perspective,” Trontelj said. These milky amphibians can live for over hundreds of years, 10 times longer than their surface ancestors, and are able to survive years of starvation. In the dark, olms also lose their color and become blind. “It is already known that this pigment loss and ocular degeneration in cavefish can be caused by several different genes, some of which are linked,” he said. Scientists have also linked this group of genes to “certain disease states of human eye degeneration and albinism.”
“Understanding these mechanisms that occur in predictable ways could also help understand some degenerative diseases in humans,” he said.
But the olms, which can now only survive in these niche habitats, are vulnerable. “These caves and groundwater are quite threatened, and sometimes even very threatened by pollution,” Trontelj said. “If we don’t describe new species, if they don’t have names, they won’t get the conservation attention that a full-fledged species might get.”
The same goes for the worms, crustaceans and sometimes even the fish that inhabit the dark recesses of the Earth.
Alejandro Martínez, head of the ANCAVE project, is working to create a database of these creatures. Its database, which already has more than 330,000 entries, draws from all references to underground cave fauna published in the scientific literature in all written languages.
“They look like things we know about from the fossil record, but are now extinct.”
— Alejandro Martinez, ANCAVE
It is called the “Stygofauna Mundi” database, in reference to a book by naturalist Lazare Botosaneanu, a pioneer in the study of these underground creatures. “We are working to make all this information publicly available,” Martínez said.
In this database, about 10% of the entries are animals of particular interest to Martínez: those that live in coastal aquifers, also called anchialine environments. What makes these underground caverns special is that their water is salty, fed from fissures and fissures underground by the nearby ocean, with a mixture of fresh water seeping in from above. These environments are found all over the world, including the Canary Islands where Martínez grew up.
And the animals they contain are unique. “Many of these animals are exclusive to this type of habitat, they are not found elsewhere,” Martínez said. They look “strange” and somehow “primitive”, he said. “They look like things we know about from the fossil record, but are now extinct.”
Others share ancestry with animals in the ocean, but their isolation in caves means they cannot interbreed, allowing scientists to compare cave dwellers with their relatives in the sun.
“(Some) resemble other animals found in the depths of the ocean today,” he said. “They are genetically close to each other, but morphologically (physically) they are very different…By comparing these types of species around the world, we can try to better understand how animals change shape to adapt to a new environment.
He himself added species to the database and, within the framework of the ANCAVE project, sampled around fifty caves in the Mediterranean, the Caribbean and several oceanic archipelagos in the Atlantic. In these caves, he measured the relative abundance of animals within them, captured some of them and then described them morphologically and genetically.
However, the database is only a first step. “We can see the generalities that occur in all of these lineages,” he explained. “We can get rid of these confounding effects of phylogeny (how a species or group evolves) and understand morphological change.”
By documenting the extent of biodiversity in underground Midnight Caves, scientists can shed light on the nature of evolution and how animals change.
But Martinez also acknowledges that the database and research into the underworld will only raise more questions. In fact, that’s why he keeps coming back to those dark, watery caverns.
The research in this article was funded by the EU.
This article originally appeared in Horizon, the European research and innovation magazine.