Bienvenidos a El Salvador! by Tyler Lawson

Thesis: Habitat Effects on Chytridiomycosis infection in the critically endangered Agalychnis moreletii

Primary Advisors: Dr. Allison Welch (Biology) and Dr. Martin Jones (Mathematics)

This past summer I was able to spend three months working on my thesis in the El Salvador. I collaborated with an El Salvadoran environmental NGO, SalvaNATURA, and its director of science conservation, Oliver Komar, to develop my thesis. After several months of working with Oliver, Allison Welch, and Martin Jones (my advisors here at CofC) we finally hashed out a plan. I was going to work with a critically endangered species of frog, the black eyed tree frog (Agalychnis moreletii). Oliver had suggested this species would be interesting to study for a couple of reasons. First, researchers discovered a couple years ago that this frog was found to be infected with an incredibly lethal fungus (Batrachochytrium dendrobatidis) which causes a disease specific to amphibians, chytridiomycosis. Chytridiomycosis, or chytrid for short, has been one of several factors involved with a catastrophic decline of amphibians all over the world. While the last study proved that this species was carrying the disease they were not able to grasp exactly how bad the frogs were being impacted since their study was carried out during the dry season when the frogs are a lot harder to find. By doing my work in the rainy season we hoped that we would be able to increase the sample size and have a better idea if chytrid was significantly impacting black eyed tree frogs.

A male black eyed tree frog calling for females from a coffee plant

Another reason this study would be intriguing is because black eyed tree frogs occur in different types of habitats. I focused on studying the frogs in natural areas, shaded coffee plantations, and sun grown coffee plantations to see if chytrid was impacting them differently in different types of habitats and also to see what the general population differences were. Knowing what is going on in the different types of coffee plantations is very important environmentally because of the way each type is generally managed. Shade grown coffee plantations keep the majority of native canopy trees intact, and use relatively little agrochemicals. In comparison, sun grown coffee plantations typically clear cut native forest and then plant their coffee. They often use heavy amounts of agrochemicals as well.

After getting some much needed financial assistance from the MES program, the CofC grad school, and a grant from the Columbus Zoo I managed to make my way down to El Salvador in mid-May to start my work!

A technified coffee plantation. You can see a few remaining native trees in the upper left corner. Otherwise this whole hillside has been replaced with coffee.

This guy was found in a sun grown coffee plantation. Earlier in the day the workers were applying pesticides which we think might have caused the burns on this guys skin.

A pond at Los Andes National Park loaded with A. moreletii!

Once I got to El Salvador I quickly discovered that I had my work cut out for me. Black eyed tree frogs are nocturnal, and sleep during the day. So that made finding them during the day tricky. I knew beforehand that they often breed around manmade structures that hold water so I focused most my efforts on finding these sites. However, there were many times when these structures either had no water, the water was too polluted, or the eggs that the frogs had layed had not yet hatched. Luckily, I had the help of an awesome herpetologist from El Salvador, Vladlen Henriquez, who was very good at finding the sites that I needed.

A black eyed tree frog sleeping under a plant.

An A. moreletii egg mass. After about a week of developing the tadpoles will drop into the water below.

A pilla inside of a shaded coffee plantation. These structures hold water and are the favorite breeding spot for my frog.

Eventually I managed to start finding tadpoles which allowed me to start the main part of my work. Chytrid affects the keratinized parts of frogs - mouthparts of tadpoles and skin of adults. I used a hand lens to look at tadpole mouths to see if they were colored (healthy) or lacking color (a sign they might have chytrid). There has been varying conclusions on how effective hand lens are at predicting chytrid since other factors can cause mouthparts to lose coloration (chemicals, temperature, etc). So part I of my thesis was to test how good mouthpart coloration predicted chytrid infection in A. moreletii. In order to test if they were in fact positive for chytrid I took a subsample of tadpoles (never more than 10% of a population), euthanized them, preserved them in ethanol, and took them back to the U.S. to perform molecular work on them. The second part of this work was testing for differences in chytrid infection between the three types of habitat I was sampling - natural areas, sun grown coffee, and shade grown coffee.

Me playing tadpole doctor

An A. moreletii tadpole. The top and right parts of the mouth are lacking color - a sign this tadpole is infected with chytrid.

Another mouthpart after being excised from a euthanized tadpole. Here you can see full coloration in the mouth - presumably healthy.

The other main part of my study involved listening to calling male frogs around reproduction sites to gauge the relative abundance of populations at different sites. This typically involved walking long distances in pouring rain. Which often was actually a lot of fun. Minus the soaking wet clothes(raincoats didnt help too much) and athletes foot.

Sweet frog love!

Once I returned to the U.S. it was time to start doing all the not so fun stuff - lab work and statistical analysis. I'm currently still in the lab trying to finish up all my molecular work on mouthparts but so far I have found some interesting results.

• Overall, the handlens worked pretty well for predicting infection with chytrid (About 85% accurate). I did find some false positives (mouthparts that lacked color but werent infected with chytrid) but these were mainly in technified plantations. We think these false positives could be a result of chemical usage in these plantations affecting the tadpoles.
• I found significantly higher levels of chytrid infection in natural areas and shaded coffee plantations in comparison to the sun grown coffee plantations. I believe this may be because the technified plantations typically had higher temperatures and more sunlight - both of which kill off chytrid.
• Population estimates from the chorus calls showed that shaded plantations had the highest populations by far. Natural areas were surprisingly low but I think this may be because I had a hard time finding reproduction sites there. Every single reproduction site I found in El Salvador was a man made one and there just aren't as many man made structures in the natural areas I sampled. Sun grown coffee plantations are presumably lower due to the drastic land use practices that are undertaken here.
• A. moreletii is currently listed as critically endangered by the IUCN due to chytrid. However, based on my study I feel that chytrid is not the most detrimental factor for this species since all the sites I sampled with high chytrid prevalence typically had high adult populations. Plus, during my whole study I could not find a single adult that showed signs of a clinical infection with chytrid. This leads me to believe that land use impacts like heavy agrochemical usage and alterating native habitat may have the biggest impact on black eyed treefrogs.

Side Adventure to Honduras!

Towards the end of the field season my frogs were getting pretty hard to find so I decided to take a road trip to Honduras for a week. Below you can see a few of the awesome pics I took while I was there!

Trachycephalus venulosus

Lake Yojoa

A bridge on a path in Cerro Azul Meambar National Park

A waterfall at Cerro Azul Meambar

I heard this tarantula walking around next to the path I was on and I thought it was a small mammal of some sort. It was about the size of a dinner plate.

Lizard - Ameiva sp.

Red eyed tree frog (Agalychnis callidryas). The more famous brother of my frog.

If you have any questions about chytrid, A. moreletii, or doing research in El Salvador feel free to Email me! - Tylaw02@hotmail.com