Bad Neighbors: How the Collateral Damage Hypothesis Modulates Predation and Parasitism Pressure in Neo-Tropical Frog Species.

Our Project:

A calling Tungara frog.

Each year, Professor Trillo brings X-SIG students to conduct research at the Smithsonian Tropical Research Institute in Gamboa, Panama. One of Dr Trillo’s research projects in Panama focuses on the role of eavesdroppers on sexual signaling in frogs. This summer, the labs’ main focus is to understand how collateral damage can influence predation and parasitism risk within a single species. Collateral damage, a concept pioneered by Dr. Trillo, refers to the dangers associated with calling near highly attractive heterospecific species. Previously, Dr. Trillo found an increase in midge parasitism for hourglass treefrogs when they called near Túngara frogs, which are highly attractive to predatory bats and parasitic midges. Dr Trillo’s hypothesis is that attractive signalers can inadvertently increase predation or parasitism on heterospecific neighbors by increasing the number of these enemies that are attracted to the aggregation as a whole.

Trachops cirrhosus, a frog eating bat.

This same idea of collateral damage across species could also be applicable within a single species, if individuals within that species use more than one type of advertisement signal, and if one of those signals is more attractive to predators and parasites than the other. This is the case for Túngara frogs. 

Corethrella, a genus of parasitic midges. These midges tend to siphon off blood through the frog’s nostrils – ouch!

When attracting a mate, Túngara frogs can modulate the complexity of their mating calls. A “simple call” (see Figure 1), which involves a whine only, is less attractive to eavesdropping predators and parasites. However, simple calls also are less attractive to potential female mates.

Conversely, Túngara frogs can produce complex calls (see Figure 1), where extra “chucks”, made of broadband sound with a greater frequency range, are produced in addition to the tonal whine. These calls are highly attractive to females, but they also increase the number of predators and parasites to the calling frog. With these ideas in mind, we hypothesize that the highly attractive complex calling Túngaras will increase the risk of predation and parasitism of their simple calling neighbors. In order to test this hypothesis, we are currently performing playbacks of simple and complex Túngara frog calls to investigate how signaling patterns of neighboring frogs change the risk of attracting eavesdropping bats and midges.

Figure 1: Comparison of frequency ranges between Tungara simple and complex calls.
Setting up a nocturnal playback trial along the Pipeline trail.

To test our hypothesis, we conduct acoustic field playback experiments to quantify bat and midge visits to complex and simple Túngara frog calls. Each night, we set up, two speakers with a combination of simple or complex calls. Our four treatments consist of simple call-simple call, complex call-complex call, simple call-complex call, or a single speaker with only one simple call. We set up camera traps to record bats visiting each speaker and we place fly traps above each speaker to collect the number of parasitic midges attracted to each type of calls. After the experiment is done, we count the number of flies present and carefully upload the bat videos taken at each site in order to score them in the future. 

Each day, after the field playbacks, we identify and count upwards of a thousand Corethrella midges.

Although we expect each experiment to run smoothly, troubleshooting is almost always necessary. Performing field work in the tropics poses unique difficulties. The humidity and heat of the tropics force us to take extra precautions with our electrical equipment. To prevent water damage due to condensation, equipment needs to be carefully stored in a heated box each night after trials. Battery charge, which could degrade quickly due to corrosion, is carefully monitored each day. Each night entails a long hike from site to site through the tropical jungle. Although collecting data in the field can be grueling, our lab is eager to see our results, and the potential effects of collateral damage on túngara frogs. 

Research off Campus

The Smithsonian Tropical Research Institute New Lab in Gamboa, Panama.

Conducting research off campus at the Smithsonian Tropical Research Institute, or STRI, in Panama offers opportunities to gain a unique perspective on academia, global research, culture and nature. STRI is one of the leading tropical research organizations where scientists come from around the world conduct field work next to the Panama canal. In Gamboa, we work alongside a closely-knit community of organismal biologists, geologists, ecologists, and other scientists dedicated to understanding and sharing information about tropical ecosystems.

Dr. Warkentin presenting at a weekly frog talk.

Each week, we go to a “frog talk” or a “Tupper talk” depending on our work schedule. These seminars are held to allow researchers in Panama to share their work and ideas, and to receive feedback from their colleagues. Frog talks, one of our lab’s favorite events, occur each Wednesday in the casual setting of a neighbor’s living room. Every week researchers of universities from a variety of different countries gather in a living room, with refreshments in hand, to listen to a speaker present their latest results. These presentations are an awesome display of cross-disciplinary and cross-cultural work: often, presentations examine biology from an interdisciplinary perspective. For instance, Dr. Warkentin, a professor in Biology and Women and Gender Studies at Boston university, gave a lecture on “queering herpetology,” which examined social biases that affected how animal behavior had been previously studied. Other talks range from examining the molecular costs of insect pheromones, to demystifying perplexing female coloration in the white-necked Jacobin hummingbirds. In all, while many assume that working in a lab as an undergraduate entails hours of repetitive tasks and uninspiring work, working at the Smithsonian Tropical Research Institute has given our lab an incredibly diversified insight into research.

Nature and Culture:

A 3-toed sloth hanging out as we made our way to the La Chunga site to set up a playback trial.
A common basilisk out and about during late-night hours.

            Aside from the questions our lab aims to answer, our surroundings have also impacted our understanding of current environmental issues. Simply put, Panama has a wealth of biodiversity. It isn’t uncommon to wake up to the raucous chorus of parrot calls each morning, to see monogamous pairs of toucans flying from tree to tree, nor to encounter a caiman during our night excursions on the pipeline hiking trail. For some of the lab members, the idea of “tropical diversity” became a tangible concept – a concept that prior to this trip had vaguely existed on the glossy pages of a National Geographic magazine.

Keel-billed toucan in Professor Trillo’ backyard.
A troop of howler monkeys passed overhead during one of our weekend hikes on the Pipeline trail.

Working in the field has also been an inherently immersive learning experience. During our first few outings, the frog chorus at experimental pond was a cacophony of croaks and whines. However, after a few weeks of nightly visits to the pond we could begin to identify the approximate number of frogs calling at the pond, their species, and the locations from which they called. We began to understand when frogs started and stopped calling or how the rain that day might affect the density of frogs that night. Likewise, as we continued our daily hiking trips through the tropical forest, we slowly began to recognize different flora and fauna, and understand how the wild plants interacted with surrounding organisms. It was as if we were slowly learning a wild language through our immersion in the tropical forest, and understanding this language helped us empathize with our surroundings.

           As we continue our project with Dr. Trillo, we are eager to analyze our data to find previously unrecognized patterns that improve our understanding of the links between predator and prey. While these last few weeks will be a whirlwind of hiking, playbacks, video viewing and fly counting, we will continue to take full advantage of our unique and incredibly beautiful surroundings.