Texas Tech University

Texas Tech Scientists Study Fear, Stress in Frogs

By: Karen Michael 

Scientists at Texas Tech University are studying fear and stress in animals to learn about novel ways in which these factors influence feeding and behavior, in hopes that information gained in their studies may be useful for developing better diagnostic tools and medications for humans.

Two of those researchers, James Carr, a professor of endocrinology, and Breanna Harris, a research assistant professor, say there are few times when animals in the wild are not surrounded by predators. The mechanisms by which prey survive are still present in humans, but can lead to anxiety, fear and stress that result in real health problems.

Prey animals can detect predators using the same senses that humans use, including vision, smell, and sound. But Carr and Harris are particularly interested in frogs. A frog's vision uses feature detecting cells that are sensitive to key features of both their prey and their predators, including size, shape, contrast, and movement.

"Frogs only have one visual system. Humans have two, and we can't separate those research-wise. It's very difficult, because both of those visual systems interact. We're interested in the subconscious visual system, which you have, but you don't know you're using," Carr said. "When frogs see things, they don't necessarily form an image the same way we think of an image. It's kind of a more reflexive thing for them. They'll see something that is the right shape and speed to be a predator, and they're programmed to do something to escape. They'll see something that's the right shape of a worm, and they're programmed to eat it."

Harris made it clear that when a frog sees movement and size that indicates there is a snake, it makes no conscious decisions on how to act on that information. The way the cues are interpreted in the brain trigger a behavior.

"We're trying to see if we can block that response," Harris said.

frog sitting on lily pad
Carr said obesity is not often found in nature – it's rare to find animals that have both the opportunity and desire to overfeed, because they are usually trying to avoid predators.

Carr said frogs will not eat something that is still. A dead fly or worm placed in front of a frog evokes no response, he said, because a frog must see movement to trigger it to eat. This is an innate behavior that frogs have "from birth," he said.

Humans share those innate abilities to identify certain dangers.

"Babies can detect snakes at birth, so there's an innate system or visual system somewhere," Carr said.

Most people either really like snakes or they don't, Carr said. Those who don't like snakes wouldn't have to think about how to react if confronted with them.

"If a bunch of snakes fell out of the ceiling all of a sudden, you'd react before you even thought," Carr said.

That's the same reaction that he and Harris see in frogs, which react immediately and instinctively to their perception of a threat.

Humans and animals are not exactly the same, but many of the same processes and pressures that shape our behavior and emotions are present in other species, Harris said.

"We're not as different as you might think," she said.

While humans share some of the same fear "pathways" in the brain, trauma and stressful events in humans can cause obesity, cardiovascular disease, immunological problems, and susceptibility to cancer, Carr said.

"These are all associated with long-term stress and anxiety," Carr said. "When we are exposed to things that give us anxiety and fear for long periods of time, it's maladaptive. It's not beneficial."

Carr said obesity is not often found in nature – it's rare to find animals that have both the opportunity and desire to overfeed, because they are usually trying to avoid predators.

"If they do get fat, they're not going to be able to run away, they're not going to be able to escape, and escape is a really important component of fear, to be able to leave the situation," he said.

That's not to say that animals cannot get fat.

"Most people think their cats and dogs are super-healthy. The vets are like, 'They're fat,'" Harris said.

Pets are reliant on what she and Carr call "hand-outs," and they also don't face a system of trade-offs in which they have to weigh the presence of food against the presence of predators.

"These things are very adaptive and very beneficial to animals in the wild when they are constantly surrounded by predators. They help the animals make decisions about when to reproduce, when to eat, and when not to get eaten by something else," Carr said.

Someday, Carr and Harris hope their research will lead to the ability to diagnose stress, anxiety, and post-traumatic stress disorder through a blood test.

"Now mental health is sort of diagnosed by questionnaire," Harris said. "People come in and they fill out a questionnaire, they talk with their care provider, and they're given a diagnosis based on that. Can we refine it? Can we use biology and what's going on biochemically to better understand these disorders?"

There is a blood test for diabetes and a treatment, Carr said. But diagnoses and treatments for mental disorders are a bit trickier.

"There's still a lot of stigma. We have a long way to go," Harris said.

Understanding how these mechanisms work in other animals could help scientists to understand how things work for humans, Carr said, referring to himself and Harris as "biology historians."

"We use animal models to learn about humans, and the reason it works is because we have a shared history," Harris said.