The Canal Zone Life: Cargo Ships and Canopy Covers
Gamboa is a small town about an hour from Panama city, packed with scientists working at the Smithsonian Tropical Research Institute (STRI). Many of the people you encounter walking through Gamboa smile at you, say hi and then go back to excavating ant nests, collecting frog foam nests, mistnetting for birds, or setting up insect traps. Everyone is doing some kind of exciting research on tropical plants and animals. This place is a biology student’s dream! There is a strong sense of community among the people here, all united by science, that makes this area so hospitable to biology newcomers. We interact with fellow interns, graduate students, postdocs, faculty and staff scientists on a daily basis. We attend weekly talks given by researchers presenting their findings to the rest of the community. Some topics have included phenotypic plasticity in hatching tadpoles of red-eye treefrogs, vibrational eavesdropping of frog-biting midges, cognitive mapping in poison dart frogs, and genomic variation and aggression in hybrids of jacana birds species. Other cool activities have included taking a workshop in R statistics and attending bi-weekly Women in Science meetings. Dr Trillo gave a talk in one of these Women in Science meetings a couple of weeks ago, and Taylor will be leading a discussion for the next meeting, the same day this blog is posted!
Being right next to the Panama Canal is a unique experience as well. It’s not uncommon to see huge cargo ships carrying large containers on our way to the field. So what do we do in this magical town of Gamboa? We are currently working on two different projects, so we are bat-frog-fly researchers by night and beetle researchers by day!
On the left, a cargo ship as it passes through the canal, on the right our nightly trek into the forest
The Bats, the frogs, and the flies – our night gig:
Túngara frogs, or Engystomops pustulosus, are an important part of the ecology of the rainforest, providing a source of food for many animals including the fringe-lipped bat, Trachops cirrhosus, and various species of snakes, herons, and other frogs. They are also often subject to parasitism from frog-biting midges of the Corethrella genus. These frogs breed in ponds or puddles, with the males producing calls to attract the females to them. One of the more interesting facts about this frog is that it has the ability to call in two different ways: a simple call, where a single whine is produced, and a complex call, consisting of the whine with the addition of another note, referred to as the chuck. Females prefer males that produce complex calls over those who only call with this whine. However, while this proves advantageous for males in terms of sexual selection, it does not come without a cost – complex calls are also more favorable for predators and parasites, increasing the male’s risk of being discovered and eaten or parasitized. The hourglass treefrog, Dendropsophus ebraccatus, is known to occupy the same ponds for breeding, which raises questions about the effects of the presence of the highly attractive túngara frogs on predation and parasitism risk for hourglass treefrogs. In a paper published in 2016, Dr. Trillo concluded that hourglass treefrogs had higher rates of parasitism by midges when the túngara frogs were calling nearby. This effect was called Collateral Damage.
Question and experimental design: This year, we want to better understand the mechanisms behind this collateral damage. Our focus is on the effects that túngara frog calling density might have on the predation and parasitism faced by hourglass treefrogs. Is the collateral damage of túngara attracting parasites to hourglass treefrogs enhanced or reduced with an increase in túngara calling density? To do this, we carry out field phonotaxis experiments. We set up speakers that play calls of both types of frogs and use IR lights and video cameras to record the frequency of bat visitations to these speakers. We also collect Corethrella flies attracted to the calls with tanglefoot traps on top of the speaker. We have three different treatments for each of seven sites: (1)“EE” treatment – a speaker playing the calls of an hourglass treefrog next to a speaker with another hourglass treefrog call, (2)“TC” treatment – a speaker playing the calls of an hourglass treefrog next to a speaker playing complex túngara calls, and (3)“MTC” treatment – a speaker playing the calls of an hourglass treefrog accompanied by five speakers playing complex túngara calls. Every day, we store all videos for later analysis and the count the number of midges that came to each speaker.
The Beetles – our day gig: Our second project looks at the ecology of anti-predator chemical defenses in tortoise beetle larvae.
Background: This study stems from the ‘escape and radiate’ hypothesis, which states that when organisms evolve a new defense mechanism to combat their predators, they become free of enemies, which allows them to conquer new niches, speciate, and diversify. Once predators eventually evolve ways to combat these defenses, the prey will evolve a novel defense again, thus repeating the cycle. This hypothesis has been previously evaluated in herbivore-plant interactions, but less is known about its relevance to predator-herbivore interactions. This year, we will be continuing last year’s research to specifically test if it is more effective for a prey species to evolve a chemical defense with a broad effectiveness against a motley of different predators, or to evolve a chemical defense with a narrow range of effectiveness to combat a single dominating predatory species. We chose tortoise beetles to answer this question because the larvae of several tortoise beetles can be impressive warriors! Using a telescoping anus, they wave around shields that include fecal matter to defend themselves both physically and chemically. It is thought that the chemicals in their shields are derived from a variety of compounds found in the plants that they eat. Our plan is to evaluate the effect of different defensive compounds found in the larvae’s shields and see how effective they are on different insect predators.
Question and experimental design: We paint mealworms, a neutral prey item, with different shield-derived chemical-compounds and present them to each of four different predators. We can then assess which chemicals provide a broad-spectrum defense against a variety of different predators and/or which chemicals provide a narrower defense against a single variety of predator. Our predators include preying mantises (Acanthops falcata and Oxyopsis gracilis), golden silk spiders (Nephila clavipes), true bugs of the family Reduviidae, and Azteca ants. We have finally collected and housed our predators and will begin the predator bioassay trials next week! We are excited to see what happens!
Everyday Life in the Field: Working on different projects means coming up the the most efficient ways to conduct our research and troubleshooting so that we can maximize our data collection for the two months that we are here. So every day is quite different! However, daily life can typically include things like:
Ø Waking up to the sound of parrots and parakeets serenading you in the early morning
Ø Feeding the local tamarin monkeys (they really like apples and bananas)
Ø Counting lots of Corethrella flies from the night before!!
Ø Collecting predators for the beetle chemistry experiment
Ø Going to hear a “frog talk” or a Tupper talk
Ø Going out at night for the phonotaxis experiments
Ø Getting bit by mosquitoes while hiking through the breathtaking rainforest to set up the speakers!
Unexpected Encounters: Sometimes while waiting for the treatments to finish, we run into some amazing tropical animals that are out in the forest! Our highlights so far include capybaras, a caiman, a coati, night monkeys, various kinds of snakes, anteaters, armadillos, and sloths! The forest is wide awake at night and booming with activity, sometimes involving wild cicada attacks (a cicada flew at Taylor’s face and has quite possibly traumatized her), frog catching (Brian’s excellent handling of Leptodactylus pentodactylus frogs), and even interrupting the filming of a horror movie! The most important thing to remember is that the forest throws unexpected challenges at you (like tree falls that block your way back to town and back up traffic for 2 hours), but you have to learn to be flexible and roll with the punches (what do you do? you walk around the tree to get ready for field work on time!).
When we take a break from science, we can go hiking or biking in the rainforest, or go to the beach. Doing things like grocery shopping and picking up equipment requires us to go across the bridge into the city, leading to another observation that, according to Taylor, Panama traffic is way worse than New Jersey traffic! Although the traffic can be frustrating, it helps to have a great group of people to talk to while you wait! It’s also common to encounter torrential downpours, and we’ve learned to accept that rain comes quite irregularly, and we embrace getting drenched (as long as we don’t have equipment with us)!
We are so grateful that every day we get to wake up to the amazing life of field biologists-in-training and want to express our gratitude to Dr. Trillo and Dr. Caldwell for letting us tag along and experience all that we can in the short time that we are here!