In this new post, Dr. Matthew Lattanzio—an Assistant Professor in the Organismal and Environmental Biology Department at Christopher Newport University, USA—discusses his recently accepted paper, “Active regulation of ultraviolet light exposure overrides thermal preference behavior in eastern fence lizards“
About the paper
Imagine for a moment you’re outside in a park, on a warm sunny day, enjoying a hike or just a relaxing break outside. Out of the corner of your eye you spot a small lizard as it climbs over to an exposed, sunny part of a large branch. It sits there for several minutes before moving back into the shade, out of sight.
You take a moment, and then think to yourself: why did the lizard move into the sun?
Most of us, and to be honest myself included up until fall 2019 (more on that below!), would answer “to warm up!” In ecology, we call that thermoregulation—the active, behavioral effort of an organism to maintain its internal body temperature. Moving into the sun warms you up and moving into the shade cools you down. When you’re an ectotherm (we used to call this cold-blooded) like a lizard, basking in the sun and shuttling between sun and shade is the way to keep your temperatures at a good level for growth, digestion, and survival, to name a few. Work in our field for over 100 years supports those observations—this is the lizard life, or so we assumed… Could there be more to this story?
Our paper centers on challenging the idea that those basking and shuttling behaviors are solely for temperature regulation. Back in fall 2019, I attended a conference geared towards zookeepers and hobbyists which focused on the husbandry of reptiles and amphibians. I had just got my university lab space set up for long-term housing of lizards; therefore, my intention was to get advice on husbandry practices. A good portion of the conference, and my discussions with the presenters, centered on proper lighting and the idea that ultraviolet (UV) light seems to be at least as important as temperature for individual lizards. Specifically, UV light is critical for lizard vitamin D3 synthesis and maintenance of proper metabolism, growth, survival, and reproductive success. Too much or too little UV is also detrimental to their health (and often fatal), just like low or high temperatures can also be dangerous. Zoos and hobbyists alike have recognized these considerations and stress the importance of UV light for captive populations. And while some fantastic foundational work by other scientists provided some early evidence that basking by chameleons may benefit their UV needs (via use of fluid-filled models), the lack of direct observations of active UV regulation for any species lingered on my mind.
Could lizards actively regulate their UV exposure?
This question was more loaded than I originally anticipated. After leaving the conference, I quickly focused on two additional questions: How can we test if UV regulation occurs? And, if it occurs, is it possible for UV needs to override temperature needs? That is, could our lizard friend have moved into the sun for UV instead of heat?
To address these questions, I needed a way to record UV exposures of lizards in real time. Available pushbutton UV sensors would not work, so I started exploring possibilities through existing data logger companies, with no luck. So, what could I do? Enter Arduino: a small-form, open-source electronics platform. The community of hobbyists using Arduino microcontrollers and related platforms is immense, and, as it turns out, there was already a need for sensors to detect and report UV exposure values (mainly for users concerned with sunburn risk). These adventures in UV took me down a path of learning to work with small-form electronics, as well as properly solder, assemble, and program my own data loggers (something I had never done before). I even went through several UV sensors before landing on the one used in our study: the key was finding a sensor that produced calibrated UV index values that matched values produced by available (and industry-standard) UV sensors. Looking back, I owe a lot of my success to the growing online hobbyist community and some prior programming experience.
Okay, back to it. Fast forward several months, and Dane (my co-author and former student [now a graduate student at Virginia Tech!]) and I were ready to start testing UV regulation behavior in lizards. We had just obtained some funding from our host university, and I had also just finished designing, assembling, and programming a UV preference data logging system. A benefit of home-made electronics lies partly in their versatility: one has full control of the program, sensor calibrations, wire gauge, and more. This nuance allowed me to ensure the sensors and wires would be light enough for the lizards in our arena, and that they would record UV exposures at the same rate as temperature values are recorded by commercial loggers.
For our study, we captured fence lizards from a local field site, estimated their body temperature and UV exposure on capture via hand-held sensors, and then transported and set them up in my lab in individual enclosures. To test UV behavioral regulation in the lab (and estimate preferred UV), we co-opted the existing established methodology for studying temperature preferences, with some slight modifications to ensure we could disentangle temperature and UV effects on lizard behavior. Specifically, over the next few weeks, we entered lizards into an experiment assessing their behavioral responses to three treatments: a gradient of temperature alone, a gradient of UV alone, and a countergradient of temperature and UV exposure. Each respective gradient ranged from low to high values (e.g., 0–20 for UV Index, ~23–50 °C for temperature), providing lizards with the opportunity to move freely in the arena and choose the temperature, or UV value, they prefer. We logged temperature values using an OMEGA data logger system (ensuring consistency with other temperature preference studies), and logged UV exposures for each lizard using my homemade UV preference logging system. Overall, lizards preferred body temperatures that overlapped with published values from prior studies, but preferred UV levels that were generally higher than what they were exposed to in the wild. These preferred values were also higher than published recommendations for fence lizard husbandry, suggesting this species may benefit from higher UV exposure in captivity.
More importantly, our design of the combined UV and temperature treatment forced lizards to choose whether to maintain their preferred body temperature, or their preferred UV exposure, but not both. Our findings revealed that lizards prioritized maintaining their preferred UV exposure at the cost of exposing themselves to higher body temperatures (~36 °C)! For perspective, prior work by other scientists has shown that these temperatures can strongly limit their ability to run, a behavior important for escape predators in the wild. Thus, it seems that for fence lizards, UV needs have the potential to override their thermal needs. This is an exciting finding that fundamentally revises our understanding of the function of basking and shuttling behaviors, revealing that there’s more to the sun than heat to a lizard.
So, what’s next? More electronics work and more data on more species! Since starting this project, I have developed field-suitable UV data loggers. I have successfully built, tested, and deployed 20 of these homemade loggers as part of a follow-up study on ornate tree lizards (so, stay tuned!). When accompanying lab preference estimates, these field-based data allow us to evaluate how well lizards can regulate to their preferred UV exposures in the wild, and what constraints (e.g., habitat complexity, elevation, or social interactions) may interfere with that ability. Inclusion of other study species is also in the cards because it is crucial for us to fully understand the nature and extent of UV regulation behavior among diverse taxa (perhaps contrasting temperature and UV needs may even explain any day-active lizard species that do not seem to thermoregulate effectively?). Finally, my lab will also soon begin collaborating with a local zoo to begin collecting data on UV regulation in their animals. It’s both humbling and exciting to be conducting research that challenges our understanding of reptile ecology in a way that could better inform academia, zoos, and hobbyists alike.
About the author
Currently, I am an Assistant Professor in the Organismal and Environmental Biology Department at Christopher Newport University, VA, USA. I have always had an interest in nature, loving camping trips and hikes as a kid, and my interest in the natural history of reptiles and amphibians has lasted just as long. My students and I are broadly interested in how reptiles and amphibians interact with, and respond to, environmental variation at various spatial and temporal scales. Most of my lab’s current research endeavors involve some incorporation of Arduino-based electronics (e.g., infrared sprint speed track, soil moisture meter, and a capacitive touch sensor boldness arena) to test our hypotheses. Over the next few years, my students and I will be continuing this UV adventure as well as assessing the climate change sensitivities of salamanders and the ecomorphological responses of lizards to urbanization. Cheers!
Enjoyed this blogpost? Read the research here!