A vigorous immune response to the chytrid fungus is associated with susceptibility to the disease

For frogs dying of the invasive chytridiomycosis disease, the leading cause of amphibian deaths worldwide, the genes responsible for protecting them may actually be leading to their demise, according to a new study published today in the journal Molecular Ecology by Smithsonian Conservation Biology Institute (SCBI) and University of Central Florida researchers.

The lowland leopard frog, found in river drainages in Arizona, is one of a few amphibian species in which some individuals survive infection by Batrachochytrium dendrobatidis chytrid fungus (Bd) while other individuals do not—even when they live in the same local population.

In a study of lowland leopard frogs infected with Bd, the fungus that causes the disease chytridiomycosis or chytrid, researchers found that frogs that died from the disease had higher expression of major histocompatibility complex and other immune system genes than frogs that survived it. Those genes help organisms fight off infections and foreign substances.

“This result was totally counterintuitive and the opposite of the pattern we expected to recover,” said Anna Savage, the study’s lead author, an associate professor in UCF’s Department of Biology and former postdoctoral fellow at SCBI’s Center for Conservation Genomics (CCG).

Comparison of differential gene expression in control, early infected, surviving and susceptible frogs in both the spleen (left) and skin (right). 

“My previous research on these immune genes showed that some variants were associated with higher survival to Batrachochytrium dendrobatidis, so I hypothesized that those genes were enabling the frogs to have a stronger immune response that would kill the fungus,” she said. “Instead, it seems like those stronger responses are linked to susceptibility, and the genes associating with survival are linked to reduced immune function.”

Savage said acquired immune responses can be very potent, require a lot of energy from the body and can sometimes produce toxic byproducts that harm the host and the pathogen.

“Immune responses are much more complex than just an on-off switch,” she said. “A big part of the immune system is regulating the type, timing and dosage of a particular response, and if any of those components get dysregulated, it can have extremely negative consequences.”

She said, for instance, Batrachochytrium dendrobatidis suppresses the host immune system by killing B and T lymphocytes. “Because those are the same cells that proliferate during acquired immune responses, producing lots of those cells might just be wasting energy on something that chytrid can easily destroy,” she said.

Amphibian populations are in decline around the world, with two-thirds of the world’s 8,000 species considered to be threatened and nearly 200 species that have already gone extinct in the last two decades. In the U.S., amphibian populations overall are declining at a rate of nearly 4 percent a year, with some areas, such as the Rocky Mountains and the West Coast, facing a higher rate of decline, according to the U.S. Geological Survey.

Although the researchers studied immune gene expression in lowland leopard frogs with chytridiomycosis, the findings may be useful for studying the disease in other frog species due to genetic similarities they share, Savage said.

 

Lowland leopard frogs were chosen for the study because their responses to chytridiomycosis vary from one individual to the next, unlike many other frog species that are completely susceptible to the disease or are completely resistant or tolerant.

This allowed the researchers to rule out genetic variation between species and pinpoint specific differences in lowland leopard frogs’ immune genes that predicted different responses to infection.

The frogs were collected in Arizona and shipped overnight to the Smithsonian’s National Zoo in Washington, D.C., where the infection experiments were conducted. Subsequent analyses of gene expression occurred at the SCBI’s Center for Conservation Genomics. Statistical analyses of the data were performed at UCF.

Robert Fleischer, senior scientist and head of the SCBI’s CCG, co-authored the study and was Savage’s main advisor for the research when she was a postdoctoral fellow at the Smithsonian. Fleischer said the results help in understanding why some frogs survive the disease and others do not.

“If we can solve this mystery, and we have taken a big step in that direction with this study, our hope and plan is to use this information to develop resources and strategies to mitigate the disease in the more susceptible species, and to counter the worldwide tide of extinction and endangerment caused by chytrid,” he said.

The researcher said the findings also show that acquired immune responses, such as those generated by vaccination, may not always be useful in combating invasive diseases of conservation concern.

Brian Gratwicke, a conservation biologist with SCBI; Katherine Hope, an associate veterinarian with the Smithsonian’s National Zoo; and Ed Bronikowski, senior curator of the Smithsonian’s National Zoo, were study co-authors as well.

The research was funded by a Smithsonian Institution Competitive Grants Program for Science grant, the Smithsonian’s Center for Conservation Genomics and a Smithsonian Institution Molecular Evolution Postdoctoral Fellowship.

Anna E. Savage, Brian Gratwicke, Katharine Hope, Edward Bronikowski, Robert C. Fleischer. Sustained immune activation is associated with susceptibility to the amphibian chytrid fungusMolecular Ecology, 2020; DOI: 10.1111/mec.15533

written by Robert Wells (University of Central Florida)

May frogs never stop singing!

In order to respond to the amphibian extinction global crisis, many initiatives to rescue endangered frogs and conserve biodiversity have been born. An example of that, is the Panama Amphibian Rescue and Conservation Project located in the Gamboa Rainforests. People may not know what we do or why we do it. But we are always there, working for the frogs, for biodiversity, for our planet. Watch this video made by PARC intern Michelle Castellanos.

 

Panamanian toads may harbor a cure for Chagas disease

Panamanian toads Rhinella centralis are distinguished by their dorsal skin covered with pointed warts. They are common along the Pacific coastal areas, often in urban areas around Panama City and small towns, and form large choruses on rainy nights. The small but strongly swollen poison glands on their heads secrete a white toxic goop. This effective defense mechanism makes predators spit them out, or froth at the mouth, vomit and it may even kill them if they try to eat the toad.

Scientists working at INDICASAT, the University of Panama and STRI began screening wild frogs for substances with pharmacological potential to treat various tropical diseases. When they analyzed secretions from these toads they discovered a chemical in the poison glands called 19-hydroxy-bufalin. They found that this chemical was very potent at killing the parasites that cause Chagas disease, and that it was not very toxic to cells. Chagas disease is a neglected tropical disease that kills 10,000 people per year, and current medications used to treat the disease are not very effective, particularly in acute cases. The fact that this chemical is quite selective with low cell toxicity means it is a promising compound that make it a candidate compound to further explore as a potential way to treat Chagas disease.

Read the research here:

Rodriguez, C., Ibáñez, R., Ng, M., Spadafora, C., Durant-Archibold, A.A. and Gutiérrez, M. 2020. 19-Hydroxy-bufalin, a major bufadienolide isolated from the parotoid gland secretions of the Panamanian endemic toad Rhinella centralis (Bufonidae), inhibits the growth of Trypanosoma cruzi. Toxicon 177:89-92.

The International Festival of the Salamander @ Boquete

Salamanders are remarkably enigmatic amphibians, both due to their often-cryptic colorations and their extremely secretive lifestyles. They are nocturnal, but even at night, one can hardly call them “active”. Many species are burrowing, and barely ever come out of their moist and dark haven created by earth and fungi. Other species prefer a life in the canopy of mysterious and often nearly inaccessible cloud forests, in a world dominated by bark, moss and lichen.

Bolitoglossa compacta, a poorly known salamander occurring at the border of Costa Rica and Panama. (CC BY-NC-ND 3.0) Marcos Ponce.

Panamanian salamanders are no exception to this rule. Herpetologists that set out to find them, regularly return after their tiring night-time missions without seeing even a trace of these wonderful creatures. Local people that work and live in areas where salamanders occur sometimes don’t even know of their existence – which is exactly why a handful of Panamanian institutions decided to organize the first International Festival of the Salamander.

The Festival took place from November 1 to 3 in Boquete, located right at the border of Volcan Barru National Park. Aptly, this is the place to be if one wants to set out on a nocturnal quest to look for them. During the days, there were photographic exhibitions, stands of the organizations involved, an interactive kids corner with movies and drawings for coloring and a small T-shirt shop, hosted by a team of volunteers that where sitting on the edge of their seats to tell you about their beloved salamanders.

A pet Boa constrictor juvenile named Oscar. One of the organizations had brought Oscar along to teach kids that although they remain wild animals, snakes can be quite gentle and docile too. © Leni Lammens.

But Friday and Saturday night, things even got better: every evening from 6 to 10 p.m., there was a free guided tour by Los Naturalistas in Volcan Barru National Park, with experts knowing where exactly chances of spotting one where highest.

The tour started off at the entrance of Volcan Barru National Park, where we met with a team of tour guides and biologists, led by Dr. Abel Batista. Then we drove on for another 3 km on a bumpy gravel road, until we were at a place known for its substantial salamander population. The first and most important part of the tour consisted of disinfecting boots and equipment, to avoid spreading diseases. After all, one of the major reasons of amphibian declines worldwide is an extremely infectious fungus, Batrachochytrium sp.. While harmless to us, for many amphibian species, it causes severe skin damage, leading to death of susceptible individuals. After sterilizing our shoes, we began measuring about a dozen environmental variables; humidity, temperature, elevation, etc.. In the meantime, the guides explained a few rules: avoid touching the animals, don’t shine too bright lights directly in their eyes and don’t take pictures of them for too long and preferably without flash.

Then, we started searching. The weather was cold, but very dry, and therefore, our subjects of interest would mostly be hiding in moist places, one of the guides explained. We adjusted our strategies accordingly, looking in small holes between rocks and gently turning branches to peer underneath. We slowly walked upwards, and over the course of 20 minutes, we had only progressed about a hundred meters. When we had nearly given up, one of the guides suddenly called us further on.

Tengo una!”

We hurried on, nearly running uphill. But with a great reward waiting for us: a nearly 20 cm long, female magnificent web-footed salamander (Bolitoglossa magnifica)  was cautiously watching us from underneath her hiding place – a thick, rotting branch covered with lichen, about a meter and a half away from the road. All excited, we had to take turns to take a look from the right angle, so you could see her. We all took a few pictures, then we stopped bothering her with our flashlights and left her in peace.

A cautious female magnificent web-footed salamander (Bolitoglossa magnifica) glaring at us from her hiding place. © Leni Lammens.

We started hiking down again, all the while scanning every hole and crevice.  We passed the cars, and soon after, someone else already shouted he had found another one. This one was more difficult to see, hiding in a small hole in between rocks and loose earth. We had barely gotten to the second, when a third one was found, and soon after even a fourth and fifth!

Biologist taking photographs of a salamander (left), while a guide in the back continues searching in other holes. (right) A magnificent web-footed salamander (Bolitoglossa magnifica) that found a hiding place behind a mushroom.

Despite the unfavorable weather conditions, our evening excursion turned out to be a great success, spotting 5 individuals of the endangered magnificent web-footed salamander in less than an hour and a half. We returned tired and quite hungry, but fully satisfied nonetheless.

Los Naturalistas are currently working on a salamander-focused guided tour, which will roughly follow a similar structure as the tour we could enjoy that night. They hope to organize a lot of similar events like the International Festival of the Salamander, to further raise awareness among tourists as well as Panamanians concerning these mysterious and intriguing animals. Salamanders are facing many threats, but in protected places like Volcan Barru National Park, they are thriving.

By Leni Lamens Herpetologist, biologist and intern at the Panama Amphibian Research and Conservation center, in collaboration with the Smithsonian Tropical Research Institute and Smithsonian National Zoological Park.

By Leni Lammens

I would like to express my gratitude towards all organizing parties involved in the International Festival of the Salamander:

Action Hub+, Bioguias Panamá, Los Naturalistas, Universidad Autónoma de Chiriquí (UNACHI), Vicerrectoria de Investigación y Posgrado (VIP)

as well as to all sponsors, without which the Festival would not have been possible.

 

Strawberry poison dart frogs prefer mates that look like their parents

A new research paper published on strawberry poison dart frogs in Bocas del Torro found that one of the reasons we have polymorphism or so many different color forms within one species of frog.  Female tadpoles prefer to mate with males that have the same color as their parents (sexual imprinting), and males defend their territories more vigorously from other males that are the same color as their parents (rival imprinting). The researchers demonstrated this experimentally by using foster parents of different color forms to raise offspring, and then tested mate or rival preference of the adult offspring.

This process of sexual selection can lead to sexual isolation even in populations that live in the same places. From an evolutionary perspective this would be a rare example of sympatric speciation, or the evolution through natural selection without geographical isolation.

Read the paper here  Yang, Y., Servedio, M.R., Richards-Zawacki, C.L., 2019. Imprinting sets the stage for speciation. Nature 574, 99–102.