To learn how poison frogs are adapting to warmer temperatures, scientists got crafty

August 02, 2019

There's a species of poison frog called the "strawberry poison frog" or the "blue jeans frog," depending on who you ask. These frogs are smaller than a quarter, with bright red bodies and navy blue limbs, and they live in shady Costa Rican forests. Or, they did, until humans began cutting the forests to create farmland. These sunny fields and pastures are hotter and drier than the forests, and scientists wanted to know how the strawberry frogs were adapting to their new environment. To figure it out, the researchers built mini temperature-controlled frog habitats to see what temperatures the frogs gravitated towards. They discovered that frogs from sunny pastures tend to seek out higher temperatures than their forest friends--but the ceiling for temperatures they can survive hasn't changed.

The project was led by two students working on NSF-funded Research Experiences for Undergraduates, first author Juana Rivera-Ordonez (University of Washington) and Adrian Manansala (University of Guam), and their mentors, Justin Nowakowski (University of California, Davis) and Michelle Thompson (Field Museum). The research overseen by senior author Brian Todd of UC Davis.

"We're trying to understand what happens to species when we transform forests for human land uses," Nowakowski, one of the corresponding authors of a paper on the project in the journal Biotropica. "For this study, we were trying to understand how strawberry poison frogs that live in these converted pastures handle warmer temperatures in these land uses compared to individuals that live in the forest."

"We found that if there's an increase in temperature, there may be some ability to acclimate or adapt, but in situations where temperatures change drastically, it may be bad news for them," says Thompson, a conservation ecologist and herpetologist at the Field Museum in Chicago and one of the co-authors of the study.

"Amphibians are really dependent on the environment for their body temperature--therefore, they're really impacted by changes to the environment," explains Thompson, who began work on the study at Florida International University. Unlike birds and mammals that can heat their own bodies to a constant temperature (like how humans stay around 98.6° F whether we're in a blizzard or a sauna), frogs are "cold-blooded." To survive in forests converted into fields and pastures, the strawberry poison frogs (aka Oophaga pumilio) camp out in the few remaining shady places like isolated trees and fallen logs.

"To do this study, we went out into pastures and the forest and measured the air temperature, and we took the temperature of frogs using an infrared thermometer--it's like a gun that takes the temperature of the frog and the substrate where the frog was," says Nowakowski. "When you go into the forest, it's really much cooler, more humid. In the pasture, you get a taste of what these frogs experience, because it's incredibly hot, and you really want to spend all your time under a tree."

"The forest has more shade, so sometimes the frogs can be found out in the open, on trees, or by digging through leaf litter. It was harder to find them in open pastures because the frogs have to really find ways to avoid prolonged sunlight exposure," says Adrian Manansala, a recent graduate of the University of Guam and one of the undergraduate authors of the paper. "The fact that our study species is a vibrant red color made it easier to spot compared to other species that might blend in to the environment. Our mentor also showed us the sound our study species makes, so after some practice we were able to distinguish the sound from others and follow these sounds to help us find them."

"To find the frogs we walked slowly, gently moving around the leaf litter to make the frogs move which allowed us to spot them," says Rivera-Ordonez, the paper's first author. "It was hard to catch them, especially without touching them. It was essential not to touch them since they are very small and their body temperature, what we were measuring, would change upon touching them."

After recording the temperatures of 111 frogs in the wild, the researchers caught 32 of the frogs by hand and brought them back to the laboratory for further research. (While some species of poison frogs are dangerous to touch, strawberry poison frogs are toxic if eaten, but safe to handle.) In the laboratory, the researchers delved into a trickier-to-measure metric: the frogs' preferred temperature.

Since they couldn't just ask the frogs what temperature they like the thermostat set to, the researchers built temperature-controlled experimental habitats using aluminum catering pans, sand, ice packs, and heating pads. "We were using whatever supplies are available in this rural area and MacGyvering it together," says Nowakowski.

The resulting frog enclosures were long rectangles with a temperature gradient, with one cold end and one hot end. The researchers put each frog into the enclosure for two and a half hours and observed the temperature where the frogs preferred to hang out. They found that the frogs taken from warm pastures chose to spend their time in a warmer part of the enclosure, while the forest frogs preferred a slightly cooler environment.

But while the frogs changed their preferred temperature, the maximum temperature they could withstand didn't change. To test the frogs' heat tolerance, they were gently exposed to rising heat levels. The researchers stopped at the first sign that the frogs were under stress: no longer righting themselves when put on their backs. (The frogs weren't harmed and were released back into the wild after the study ended.)

No matter where they were from, the frogs got too hot at about the same temperature. That means that while the frogs can adapt to have different preferred temperatures based on what they're used to, the upper limit of what their bodies can tolerate is a hard line. "It appears that for the time being, this species can eke out a living in these converted habitats using different behaviors to avoid extreme temperatures. But this is all subject to change," says Nowakowski. "On top of habitat change, temperatures are rising due to climate change. We don't expect things to stay at the status quo--these frogs are bumping right up against their thermal tolerances, and it's unclear whether they'll persist or not."

The frogs' maximum temperature limit being seemingly fixed makes long-term climate changes more dangerous for them, but Thompson notes that there is hope in the way the frogs can adapt on the short term to habitat change.

"In the current biodiversity crisis that we're a part of, we have to think of ways to make changes for positive impact," says Thompson. "This is something we can act on. Where habitat conversion cannot be avoided, leaving small pockets of vegetation will let small populations of frogs persist. It shows that people can make a change."

And in addition to the potential of the study to help frogs and other animals, the researchers emphasize the importance of the REU program the students took part in. "You can learn a lot about science and research in the classroom, but it's really all abstract until you go into the tropical forest or the laboratory," says Nowakowski. "You learn how to develop questions and collect data to answer those questions. For students, it can be really transformative and eye-opening."

"The REU was an unforgettable experience," says Manansala. "Before this research program, I had never caught frogs or even held one before, so doing this research was a very new experience for me. This program was my first time conducting an independent study and before this, I had never thought of using creative ways to conduct research such as using a tea kettle and buckets of ice cubes to manually control the temperature of a lab trial. This program taught me research skills and knowledge that I still use today and will continue to apply in a future career in science."

"One distinct aspect of an REU is how as an undergrad you are able to do more than the data collection. In this program you work with a mentor to develop questions, design the experiments, carry them out, and interpret your results. This makes a huge difference for students and gave me the opportunity to extend this work into my senior thesis, eventually leading to this publication," says Rivera-Ordonez. "This experience was a great step towards my goal of attending graduate school and it allowed me to solidify my interest in herpetology and in the study of how human driven changes affect them."

Field Museum

Related Science Articles from Brightsurf:

75 science societies urge the education department to base Title IX sexual harassment regulations on evidence and science
The American Educational Research Association (AERA) and the American Association for the Advancement of Science (AAAS) today led 75 scientific societies in submitting comments on the US Department of Education's proposed changes to Title IX regulations.

Science/Science Careers' survey ranks top biotech, biopharma, and pharma employers
The Science and Science Careers' 2018 annual Top Employers Survey polled employees in the biotechnology, biopharmaceutical, pharmaceutical, and related industries to determine the 20 best employers in these industries as well as their driving characteristics.

Science in the palm of your hand: How citizen science transforms passive learners
Citizen science projects can engage even children who previously were not interested in science.

Applied science may yield more translational research publications than basic science
While translational research can happen at any stage of the research process, a recent investigation of behavioral and social science research awards granted by the NIH between 2008 and 2014 revealed that applied science yielded a higher volume of translational research publications than basic science, according to a study published May 9, 2018 in the open-access journal PLOS ONE by Xueying Han from the Science and Technology Policy Institute, USA, and colleagues.

Prominent academics, including Salk's Thomas Albright, call for more science in forensic science
Six scientists who recently served on the National Commission on Forensic Science are calling on the scientific community at large to advocate for increased research and financial support of forensic science as well as the introduction of empirical testing requirements to ensure the validity of outcomes.

World Science Forum 2017 Jordan issues Science for Peace Declaration
On behalf of the coordinating organizations responsible for delivering the World Science Forum Jordan, the concluding Science for Peace Declaration issued at the Dead Sea represents a global call for action to science and society to build a future that promises greater equality, security and opportunity for all, and in which science plays an increasingly prominent role as an enabler of fair and sustainable development.

PETA science group promotes animal-free science at society of toxicology conference
The PETA International Science Consortium Ltd. is presenting two posters on animal-free methods for testing inhalation toxicity at the 56th annual Society of Toxicology (SOT) meeting March 12 to 16, 2017, in Baltimore, Maryland.

Citizen Science in the Digital Age: Rhetoric, Science and Public Engagement
James Wynn's timely investigation highlights scientific studies grounded in publicly gathered data and probes the rhetoric these studies employ.

Science/Science Careers' survey ranks top biotech, pharma, and biopharma employers
The Science and Science Careers' 2016 annual Top Employers Survey polled employees in the biotechnology, biopharmaceutical, pharmaceutical, and related industries to determine the 20 best employers in these industries as well as their driving characteristics.

Three natural science professors win TJ Park Science Fellowship
Professor Jung-Min Kee (Department of Chemistry, UNIST), Professor Kyudong Choi (Department of Mathematical Sciences, UNIST), and Professor Kwanpyo Kim (Department of Physics, UNIST) are the recipients of the Cheong-Am (TJ Park) Science Fellowship of the year 2016.

Read More: Science News and Science Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.