How environment affects the welfare of salamanders across their lifetimes: Tom Luhring and Caitlin Gabor

A western lesser siren (Siren intermedia nettingi) found in Illinois. Photo credit: Peter Paplanus.

August 4, 2022

When Caitlin Gabor wrote on social media that she’d be working on a project with lesser sirens, the post didn’t receive a lot of attention until a relative asked, “What is a siren?”

“Then people started commenting, and I realized I had some explaining to do,” says Gabor, a biology professor at Texas State University.

Abundant yet reclusive, lesser sirens (Siren intermedia) are a type of aquatic salamander common throughout the eastern half of the United States and northeastern Mexico. They spend their days nestled in the mud at the bottom of ponds and other still bodies of water, becoming more active at night. They’re so inconspicuous that many people have never heard of them. 

Using Wild Animal Initiative funding, Gabor, Wichita State University Assistant Professor Tom Luhring, and Stephen F. Austin State University Assistant Professor Christopher Schalk plan to study four populations of lesser sirens in Texas with an eye towards welfare, measuring hormones in the secretions of individual sirens to track their stress at different points in their lifespans and compare hormone profiles between populations. The study will also compare stress responses from two marking techniques and evaluate the welfare impacts of each method.

WHY WE FUNDED THIS PROJECT

Juvenile sirens are the focus of this study because young amphibians are particularly vulnerable to stressors and because juveniles are so abundant among amphibians. Moreover, the lesser siren is an abundant and relatively neglected species. Sirens’ needs change throughout their lives, and therefore it is plausible that their welfare does, as well. This project will apply a novel, less invasive method as part of a longitudinal experimental design, allowing the researchers to measure the physiological stress of sirens and how it changes over the course of an individual’s development.

Abundant yet elusive

“By trying to figure out a way to measure quality of life, we’re filling in some of the gaps in our knowledge of this underappreciated, hidden species.” —Tom Luhring

Photo courtesy Tom Luhring.

The hidden nature of amphibians might contribute to the lack of research on them, Luhring says. He’s studied sirens since 2006, and in that time, he’s developed an appreciation for the enigmatic aquatic salamanders with feathery gills and smooth, eel-like bodies. 

Their lives are something of a mystery, including how they experience the world. From previous studies, Luhring knows that lesser sirens face serious challenges in their environment — everything from temperature extremes to droughts and bite wounds from fellow sirens. But to understand how individual sirens subjectively experience these events, he recognizes a need for further research. 

Luhring describes his first encounter with sirens as a “happy accident,” since he was actually looking for mud snakes when he happened upon the nocturnal aquatic salamanders. When he kept finding greater sirens instead of the mud snakes he was targeting, he decided to take advantage of the situation and focus his attention on the amphibians.

“Come to find out, there was so little work done on them that basically anything I learned about them was new,” he says.

Amphibians are fascinating animals, Luhring and Gabor say, and sirens are particularly interesting, with a single pair of front legs and no terrestrial life stage, unlike many other species of frogs and salamanders. Even though they’re numerous, amphibians don’t feature in research studies as often as birds and mammals.

“They’re just not as obvious to us,” Luhring points out. “We don’t see amphibians singing in trees or running in front of your car. You might see a deer or where a beaver built a dam, but you don’t always see evidence of amphibians.”

Variations across time

“We need to take a proactive approach to understanding [amphibians] and from an individual perspective.” —Caitlin Gabor

Photo courtesy Caitlin Gabor.

As they undertake the first longitudinal, individual-level study of coping capacity in wild juvenile sirens, the researchers have an exciting challenge ahead of them. Over several study years, they will set up soft mesh traps in two Texas national forests to catch lesser sirens when they are most active at night. 

The study sites feature pine forests with ponds interspersed among the trees. When checking pond traps in the morning, the team will anesthetize each individual upon first encounter and use passive integrated transponders (PIT) tags to mark the sirens, allowing them to recognize and make multiple observations of individual sirens across the study period. 

Despite their elusiveness, lesser sirens have several characteristics that make them especially good study subjects for understanding wild animal welfare. It’s important to track individuals when studying welfare, and because sirens don’t leave their ponds, researchers can expect to find them in the same pool each time they look. Compared to amphibians like frogs, who can wander from pond to pond or leave the study site entirely, this feature of wild sirens makes it easier to track individuals over time. 

Another useful feature for studying welfare is that amphibians passively release hormones through their skin, and because they live in water, researchers can place them in a clean, water-filled receptacle to collect their sample without needing to undergo more invasive procedures. Their excretions, including feces, urine, and mucus, contain corticosterone, a water-borne stress hormone that can indicate how stressed an individual siren might be at the time of measurement. Unlike plasma samples, which are point measures, water-borne hormones can reveal more than the animal’s immediate state and reflect the animal’s experiences from days in the past, Gabor says. 

Corticosterone interpretation can be complicated and can vary across species. That’s why the researchers plan to use additional indicators of welfare, such as injury prevalence, increased rates of aggression, and body condition. Together, these observations can paint a fuller picture of typical life experiences for lesser sirens, including how environmental changes like droughts affect them.

When the team catches the same siren again, they will scan the PIT tag and record characteristics about the individual. After collecting hormone samples, researchers will release the sirens back to their ponds until the next sampling period. These repeated measurements are designed to capture the full variations of an individual siren’s positive and negative experiences as they change over time, from juvenile to adult. 

Gabor says there’s so much more to wild animal welfare than measuring life or death, and by looking at the in-between range of subjective experiences, we might be able to detect signals about their state of health before high-mortality events happen.

“We can see birds flying into windows and realize we need to put something up so they can avoid the window, but with amphibians, you often don’t get any of those signals because they’re completely out of view,” Gabor says. “We need to take a proactive approach to understanding them and from an individual perspective.” 

Tracking individuals

Tom Luhring (center) and his colleagues also study greater sirens (Siren lacertina). Photo courtesy Tom Luhring.

The team can collect hormone samples from the sirens by measuring their waterborne excretions, avoiding the need to take blood samples. The PIT tags for keeping track of individual sirens, however, will require the insertion of a microchip just beneath the siren’s skin, which is why the team will anesthetize the sirens before they undergo the procedure. Luhring and Gabor will also study how stressful the sirens find this marking method compared to another, seemingly less invasive method using photo identification. 

“For large animals like whales, you can track individuals from a distance by looking for unique markings on their flukes,” Luhring points out. “For an amphibian, you need to restrain them on each encounter to get a high-quality photo of their unique markings, and it’s possible that it’s actually more stressful for the animal than a PIT tag.” 

Graduate students will lead this part of the project. First, they need to establish how well pattern recognition software works to identify individual lesser sirens. Then, they will compare stress responses between sirens identified through photographs and sirens identified through PIT tags. 

Because no one has studied how these methods affect siren welfare, and the sirens can't tell us themselves, it is critical to study the stress response of individual animals to the procedures in order to avoid doing harm to animals involved in studies going forward.

Since researchers commonly use both methods in the field, “it could help inform future studies that use these techniques,” Luhring says. 

Results might take years to achieve, but for a longitudinal study that measures changes in welfare over time and across populations, it’s all part of the process. With so many unique aspects to this project, Luhring says he hopes their scientific contribution will help researchers better understand what life is like for the secretive lesser sirens, who serve as amphibian ambassadors for their understudied class.

“By trying to figure out a way to measure quality of life, we’re filling in some of the gaps in our knowledge of this underappreciated, hidden species,” Luhring says.

The study site will resemble this one, with ponds interspersed among the trees. Photo courtesy Tom Luhring.

RELATED RESEARCH

This 2020 paper describes some of Gabor’s work on noninvasive hormone sampling methods for amphibians: “Stressed tadpoles mount more efficient glucocorticoid negative feedback in anthropogenic habitats due to phenotypic plasticity.” This 2015 paper features some of Luhring’s work on sirens: “Trade-offs between growth and maturation: the cost of reproduction for surviving environmental extremes.”

This is the fourth story in a series of features on our spring 2022 cohort of grantees. Please subscribe to our newsletter to get future stories delivered straight to your inbox.