To Call, or Not To Call, That is the Question

To Call, or Not To Call, That is the Question

The Trillo Lab and The Caldwell Lab 

Tiana Norris and Arden Dowd 

Professors Trillo and Caldwell conduct most of their research at the Smithsonian Tropical Research Institute in Panama, so their X-SIG students get a unique experience in a tropical country. This year, Professors Trillo and Caldwell are collaborating on a project funded by the Smithsonian that looks at how hourglass treefrog call behavior changes based on the calls of heterospecific neighbors. 

Research Background: 

In a previous study with hourglass treefrogs, Dendropsophus ebraccatus, and túngara frogs, Engystomops pustulosus, Dr. Trillo demonstrated that nearby signalers of an attractive species, such as túngara frogs, can drastically alter the risks of attracting eavesdropping parasites to less attractive species, such as hourglass treefrogs– a phenomenon called ‘collateral damage’. This summer we are especially focusing on calling behavior changes and spatial shifts in hourglass treefrogs in response to calling túngara frog neighbors.  

Methods and Research:

To investigate changes in calling behavior of hourglass treefrogs due to the identity of their calling neighbors, we are carrying out three different experiments that examine the calling behavior and dispersion of hourglass treefrogs both spatially (vertically and horizontally) as well as temporally: 

(1) AudioMoth recordings: To understand the natural calling behavior of hourglass treefrogs and túngara frogs in Gamboa ponds, we placed sound recorders called AudioMoth in two different locations where the two species are known to call in mixed-choruses. We retrieve the AudioMoths every other night and note the species present at the time of collection. Recordings from these AudioMoths give us information as to where, and when these species are calling from, demonstrating that the two species can be present and active at the same time. 

(2) Acoustic camera recordings: The acoustic camera is a device equipped with both visible light and infrared cameras as well as an array of microphones. The circular array of microphones surrounds the camera and is sensitive to a broad range of sound frequencies.  Combining information from the microphone array and the infrared camera can help us pinpoint the location of calling frogs, and give us information about when sounds are made, how frequently they occur, and their amplitude. We record the output of the acoustic camera onto a laptop computer for future analysis. In our experiment, this camera is used to track hourglass treefrog calls and the location of those calls in the presence and absence of a túngara playback.  

To conduct this experiment, we find a focal male hourglass treefrog In a pond and set up two tripods around him: one with a speaker about a meter away, and one with the acoustic camera four meters away. There are two different treatments: No playback, and túngara playback. No-playback trials consist of five minutes of adjustment time, followed by five minutes of recording, and then three additional recordings every five minutes. This treatment helps us get a baseline of hourglass treefrog calling behavior in the absence of nearby túngaras. Playback trials have the same five minutes of adjustment time and five minutes of recording, but then at the start of the second recording, a túngara call is played from the speaker every second for the final three recordings. After the trials are over, fly strips are placed on the speaker and a five-minute túngara playback is played. This is done to give us an idea of the number of parasitic flies present that night. As this part of the experiment is done in a natural setting, it gives us an idea of whether hourglass treefrogs change their behavior in response to the presence of túngara calls, whether that be the timing of calls, types of calls, or movement of the focal individuals. 

The left is an example of what we see when the frog calls, a red circle will emit from its location indicating a high frequency. A deep red means loud noise, and the scale falls down to a light blue which indicates the opposite.  

(3) Mesocosm experiment: For this experiment, we collect three hourglass treefrogs each night and put them in a mesocosm enclosure. We spent around three weeks creating this enclosure, from picking out the framing and mesh to sewing the mesh to itself and to velcro to allow for an easily transportable enclosure. Our mesocosm is 3x3m^2 wide and 1.5m tall, with the floor and one corner being detachable to allow for entrance and exit. This enclosure contains a small circular pool with water and vegetation that is readily accessible for these hourglass treefrogs. We let the frogs acclimatize to this new environment for 24 hours and start the experiment the next night, where we conduct one of two different treatments. In one of the treatments, we first find the frogs in the pool, record plant location, height in the plant and whether they are calling, We then start a túngara call playback and record any changes in call behavior, plant height, and plant location every hour for a total of two hours. In the second treatment, we collect all the same information, except we do not have a túngara playback. This experiment will allow us to see in more detail any changes in calling behavior and dispersion of hourglass treefrogs in response to calling túngara neighbors. 

Doing research in Panama! 

We live and do our research right by the Panama Canal in a town called Gamboa. This area has a clear US influence due to the history of the US in the Canal and many US citizens previously associated with the canal still live here. Gamboa is a quiet small town next to the Soberania National Park where many STRI temporary or long-term researchers as well as staff scientitsts live. This is not only because of the quick access to Soberania National Park and because this habitat attracts researchers around the globe, but also because we are next to Barro Colorado Island, one of the most important sites for tropical biology research in the world, and to one of the largest STRI owned laboratories in Panama.  

The Smithsonian Tropical Research Institute has at any one time, a large number of scientists working there. All these scientists are at very different stages, we meet undergraduate interns, post-doc interns, graduate students, postdoctoral researchers and PIs, all doing tropical biology research in a wide variety of organisms, from insects to frogs, to bats, to whales. This network of research and researchers is important to our visit here because there are many opportunities to engage with other tropical research projects and researchers.

Tiana’s Panama Experience  

My Panamá journey has been a series of first times. On the first day, I took a plane by myself for the first time, used my passport for the first time, and settled into an apartment for the first time. During this trip I saw many tropical animals for the first time. For example, the first morning here I saw a family of agoutis, which are large rodents with a face similar to capybara. I’ve also learned a lot about katydid insects thanks to our postdoctoral fellow, Ciara. A lot of her Ph.D. work is centered on them. The wildlife here never ceases to amaze me. One night on a hiking trail, we stood in amazement staring at a tarantula on a tree. On another day I saw a beautiful toucan right above me in a tree while I was walking from STRI to my apartment. I also see monkeys all the time. I have seen white-faced capuchins, tamarins, and howlers. I could go on forever about all the different tree frogs I see: my favorite are gladiator frogs.  

The wildlife is not the only amazing thing in Panamá though. I’ve met a lot of passionate researchers and been inspired by their projects. In June our team went to a Fellow’s Symposium at Tupper Auditorium. I watched project presentations in awe and later got to talk with the researchers. That is how I met staff scientist Sabrina Amador. She was so encouraging and invited me to visit her interns in the lab. They thoroughly explained the mutualistic relationship between ants and fungi and described parasitic behavior while they showed me their colonies. I also went into the field with them to check on their alate ant traps and to determine the health of the marked colonies. I encountered more researchers at Barro Colorado Island, where I watched a fascinating talk on frog partitioning in the various frequencies of their environment which I got to relate to the project we are doing. I’ve been faced with many opportunities here to further explore my interests and discover new ones and made connections that open up so many different paths.   

I came to Panamá for my first internship and have gained a lot of tropical field experience and knowledge, but I’ve also had time for other fun activities. Our team went to a pride festival where we got close with other people from STRI and met some friendly Panamanian people. During the march, I got to see gorgeous views of Panama City and the Pacific Ocean. It was my first time seeing the Pacific Ocean. Afterward, we went out to eat good Mexican food. The best food I have had here though was on my birthday after seeing Barbie in theaters with Arden, Michael, and Alex. We went to a restaurant called Tantalo in an area of Panama called Casco Viejo, where we ordered duck, salmon, octopus, brussel sprouts, salad, and beef sliders. I think about that meal daily. Another activity I enjoy is practicing my Spanish with native speakers. I  get to practice my Spanish whenever I order lunch meat at the grocery store or when I go to STRI’s get-togethers with other researchers. All these moments are special to me. I could not possibly fit every meaningful experience I’ve had in Panamá into this blog. I’ve had such priceless interactions here and gained so much knowledge! 

Arden’s Panamanian Experience! 

Here in Gamboa, every day is different, living in a town where curiosity is fostered by amazing locals and scientists of every caliber, leading to many different activities, interactions, and opportunities – and none of that includes the amazing wildlife that lives here! (I mean, we have 20 agouties as neighbors, see monkeys daily, chase frogs, and are chased by birds, what more could you want?) 

The first several weeks of our time here were spent sewing our mesocosm, driving to the city to buy supplies for our projects, and running pilot experiments in the evenings. These tests consisted of things from using a funnel for female frogs made from a plastic bowl to finding ideal sampling times, to learning how to use the acoustic camera’s technology. Now that we are more settled into a routine, the afternoon is spent exploring Panama, learning from scientists both in and out of the bat lab, and relaxing by the pool at the Gamboa Resort. The night, however, is a different story, we capture males for the mesocosm, and females for a separate experiment, wade into Kent’s marsh for acoustic camera sampling, and trek into the forest for the Audiomonths. 

​ We have had the opportunity to attend many talks in our time here at STRI. We attend weekly Frog Talks, where scientists present their research on topics ranging from frogs to katydids! We also attended the Fellows Symposium at STRI’s headquarters where we listened to some incredible presentations. The topics ranged from knitting as a way to connect with nature and to educate on the importance of science and communication, to our understanding of sharks’ roles throughout time, to trade through Panama as seen through pottery. These only give a glimpse of what we have been exposed to here at STRI, but hopefully, demonstrate the variety of interests and studies that happens here at STRI. 

​ When we aren’t in the field or auditorium, we go on day trips to explore the surrounding areas. We have seen the tropical forest in its glory on some beautiful hikes, experienced the Panama Canal, watch huge boats move through the locks, and experienced some of the nightlife as well! One of the biggest highlights of this trip for me was when I was able to join the Bat Lab on a netting trip, where we traveled to a near-by cave system to catch Phyllostomus hastatus, or the greater spear-nosed bats. They were really big, around 120 grams, and had incredibly strong wings and jaws, but at the end of the day, they really just wanted eat bananas and sleep

Recently, we had the opportunity to visit Barro Colorado Island (BCI) a STRi facility located in the Panama Canal. We were able to visit because a Bambi Talk was being held that day. Bambi Talks are similar in idea to Frog Talks, where people present their research. Before attending the talk, Tiana, Michael, and I went on a hike around the island and got to see a howler monkey troop up close along with a crested guan, and a wide variety of other taxa! After our hike, we attended a talk on the analysis of frog sound partitioning based off previous studies. 

​ There are still two weeks left here in Panama, and we are determined to make the most of it. Our research is still ongoing, and in our time off we will keep exploring Panama, and will be participating in two outreach opportunities, one with the local zoo for Golden Frog Day, and one where we will present our preliminary research to the public on bat-night!