Vulnerable Salamanders, Key to Healthy Ecosystems, a Focus in Two Studies

Lessons about interactions between habitat, evolution and tiny, vulnerable species—who matter more than you might think for people who share space with them—have emerged from two separate studies published by researchers involved with The University of Texas at Austin’s Texas Field Station Network and Biodiversity Center. 

From different angles, scientists examined the fates of two types of salamanders in Central Texas: Ambystoma salamanders, which play an important role in soil health and ecosystem resilience in many parts of the U.S., and Eureycea salamanders, known to be important to water quality necessary in the aquifers that provide Texans with drinking water.

Weathering Change

As rising temperatures puts pressure on living things in Texas, fossil records offer lessons on how salamanders have fared with similar changes in the past, according to a new study published in the journal Quaternary Research and supported by UT Austin’s Planet Texas 2050.

Using fossils dating back thousands of years, the study’s authors found lessons from other periods with hotter, drier weather similar to what climate models predict lies ahead for Texas. Weather then must have led to the evaporation of ponds and streams and the permanent disappearance of some salamanders from the region.

Salamanders rely on streams, lakes and similar bodies of water to reproduce and thrive, and they make up a key portion of the food web, serving as predators of small insects and as prey for different types of fish, birds and mammals. David Ledesma, an author on the study who received his Ph.D. from UT along with his advisor integrative biologist Melissa Kemp, worked with fossils from the Texas Vertebrate Paleontology Laboratory that were excavated from Hall’s Cave in the Edwards Plateau region west of Austin. Ledesma identified thousands of fossils of a type of tiger salamander once abundant here in the Late Pleistocene, 20,000 to 11,700 years ago, though they declined and apparently disappeared altogether regionally about 6,000 years ago. 

“This cave site represents the last known occurrence of these salamanders in Central Texas,” Ledesma said. 

To investigate the disappearance of the salamanders, Ledesma correlated the presence of salamanders within time packets of sediment in the cave with environmental changes that occurred in the past. 

“Six thousand years ago, the environment was much hotter and drier than it was in the Late Pleistocene,” Ledesma said. “I also found another isotope record that indicated there was a lot of soil erosion from 11,000 years ago to 6,000 years ago. Suddenly, the soil, which normally would have supported plant life and kept moisture in, was no longer there.”

Tiger salamanders, which are part of the genus Ambystoma, like to burrow in deep, moist soil, and their doing so can contribute to soil health. Ledesma said the disappearance of the moist-soil habitat, combined with decreased precipitation and increased temperatures, likely drove the salamanders’ disappearance. Even after the moister conditions required for tiger salamanders returned, they failed to recolonize the area. This suggests that such sensitive species, when affected by extreme weather, may not always rebound with resilience. 

“Once they’re gone, we can’t expect them to come back on their own,” Ledesma said. “If these salamanders lose important water habitats, we can expect them to disappear and probably not return.”

Ledesma said conservation strategies like preserving creeks, streams and lakes are important to protect salamanders as climate conditions deteriorate.

“Having water features in relatively close proximity will help salamanders have gene flow between populations to maintain healthy genetic diversity and allow them to traverse an area which would otherwise be much more treacherous,” Ledesma said. 

UT Austin’s Kyle J. Moxley joined Ledesma and Kemp on the paper.

Canaries in a Coal Mine 

Other new findings have been linked to one of the most biologically diverse cave ecosystems in the world: the Edwards-Trinity aquifer system of Central Texas. This region is home to more than a dozen species of aquatic, permanently larval salamanders, many of which are found only in Central Texas and are endangered or threatened due to habitat degradation and water quality concerns. 

“These salamanders are like canaries in the coal mine for the aquifer,” said Ruben Tovar, who received his Ph.D. in May from UT Austin. “Their survival depends on clean, healthy groundwater—which is the same water we drink.”

A notable feature of these creatures dwelling in our dark, watery caves is that many of them have no eyes. In fact, species after species of salamander has traded eyesight for specialized sensory organs that detect movement and pressure in water, according to a recent study with potential applications for human health, first authored by Tovar. The study appeared in the Proceedings of the National Academy of Sciences and received support from the National Science Foundation.

“We’re sitting on one of the most diverse groups of subterranean salamanders in the world,” Tovar said. “They might look strange, but they have a lot to teach us—about evolution, about ecosystems and maybe even about ourselves.”

The study documents how in different lineages of Eureycea salamanders a pattern of parallel evolution has been established. Different species’ repeated and independent transition to life underground involved physical and sensory adaptations that help them navigate a world of total darkness. 

“This is about evolution and adaptation to perpetual darkness—the loss of one sensory organ and the compensation by another,” Tovar said. “It’s not the end of the story, but it’s a big part of it.”

Using an imaging technique called diceCT scanning, the researchers captured 3D images of soft tissues inside salamander heads to measure eye volume and locate tiny mechanosensory organs called neuromasts, which detect movement and subtle changes in water pressure. These are found also in sensory systems for fish and other larval amphibia.

“We found that salamanders with reduced or no eyes developed more neuromasts,” Tovar said. “It’s a clear example of sensory compensation. If you can’t rely on vision, evolution finds another way.” 

The study analyzed developmental stages throughout life and discovered that all salamanders begin life as hatchlings with similar eye development. But for cave-dwelling species, eye growth stalls and begins to regress while neuromasts expand, especially in regions of the head that vary by species, suggesting multiple independent pathways to sensory adaptation.

“We weren’t even looking for neuromasts at first. It was a complete surprise,” Tovar said. “But once we noticed them, we realized they might be the key to understanding how these salamanders navigate their world without sight.”

The research also examined the expression of PAX6, a gene known for its role in eye development across vertebrates. Surprisingly, the gene remained active in the enhanced neuromasts of blind salamanders but faded in their surface-dwelling relatives.

“These salamanders naturally reduce their eye development in a way that’s not typically harmful,” Tovar said. “Studying that might give us insight into what happens when eye development goes wrong in humans.”

 The PAX6 gene is a well-known developmental regulator in animals, including humans. Mutations in this gene are linked to several forms of congenital blindness, such as aniridia, a rare condition where the iris is underdeveloped or absent. By studying how PAX6 behaves in salamanders that naturally lose their eyesight during development, scientists hope to gain insights into the genetic and molecular mechanisms behind vision loss in humans.

“We’re looking at a natural experiment in eye reduction that unfolds without causing disease or death,” Tovar said. “It’s a rare opportunity to understand how vision can be dialed down biologically—and maybe uncover clues relevant to human health.”

Brittany A. Dobbins, Nicholas R. Hartman, Sheena Leelani, Thomas J. Devitt, David C. Cannatella and Biodiversity Center director David M. Hillis of UT Austin, Dana M. García of Texas State University and Paul M. Gignac of University of Arizona were also authors on the paper.