The global status of Harlequin frogs

Our planet is home to almost 9,000 amphibian species. For more than 100 years, these animals have dramatically suffered the consequences of deforestation, agriculture, wetland drainage, agrochemicals and other pollutants. In recent times, new threats have emerged making 40% of all amphibian species threatened with extinction under “Red List” released by the International Union for the Conservation of Nature (IUCN), which was recently updated. New threats include climate change and emerging infectious diseases. Among them, amphibian chytrid fungi causing skin infections play a key role. These fungi have been spread all over the world by humans and induce the disease chytridiomycosis in amphibians, leading to population declines and even extinctions.

Toad Mountain harlequin frogs from  the Darien.

Already 30 years ago, researchers, conservationists and other stakeholders have realized the crisis the amphibians are in. Various initiatives, at the global, regional and local scales have been founded to safeguard amphibian diversity including numerous management and action plans. Due to these activities, we massively augmented our knowledge about where declines happen, as well as the mechanisms behind these and how threats interact. This goes hand in hand with enormous engagement for protecting natural habitats and accompanying captive breeding in conservation facilities. Also, diseases and their agents are much better understood. There have been many stories of success and without all the investment, work and passion of dedicated actors many amphibian species would have become extinct by now!

However, it is difficult to appreciate where we stand in overcoming the amphibian crisis. Threats and the vulnerability to them are not equally distributed over all species. Certain amphibians are more susceptible and suffer more. They represent ‘worst-case scenarios’ of the amphibian crisis. For many of them, we lack sufficient information to access their current status. Not so for harlequin toads, genus Atelopus, from Central and South America. These are small, often colourful and day-active animals that inhabit lowland rainforests to high Andean moorlands (páramos) above tree line.

More than 130 Atelopus species are known and – being highly sensitive to threats – many of them have declined and are even feared extinct. Harlequin toads are the poster child of the amphibian crisis, and due to their iconic appearance, scientists have studied population status data since the early 1990s. In a recent study published in Communications Earth and Environment, Lötters and 99 colleagues, mostly conservationists and researchers from countries where harlequin toads naturally occur, compared population status data as of 2004 and of 2022 to examine species-specific trends over the last two decades.

Data from the authors confirm that massive conservation efforts from many scientists, conservationists and local communities have revealed that more than 30 Atelopus species that in part were feared to have vanished are still there! However, evidence suggests that at the same time all species remain threatened and their conservation status has not improved. Factors threatening the remaining harlequin toads remain unchanged and include habitat change and chytrid fungus spread. In addition, the authors demonstrated that in the future harlequin toads suffer from climate change.

Authors conclude that other worst-case amphibians continue to be imperilled demonstrating that the amphibian crisis is still an emergency. Thanks to the tremendous strength put into conservation, by collaborative networks like the recently launched Atelopus Survival Initiative under the umbrella of the Atelopus Task Force of the IUCN Amphibian Specialist Group, these amphibians have not yet vanished. It is now more than ever critical to continue and increase efforts to escape the emergency the amphibian crisis still is.

Lötters, S., A. Plewnia, A. Catenazzi, K. Neam, A.R. Acosta-Galvis, Y. Alarcon Vela, J.P. Allen, J.O. Alfaro Segundo, A. de Lourdes Almendáriz Cabezas, G. Alvarado Barboza, K.R. Alves-Silva, M. Anganoy-Criollo, E. Arbeláez Ortiz, J.D. Arpi L., A. Arteaga, O. Ballestas, D. Barrera Moscoso, J.D. Barros-Castañeda, A. Batista, M.H. Bernal, E. Betancourt, Y.O. da Cunha Bitar, P. Böning, L. Bravo-Valencia, J.F. Cáceres Andrade, D. Cadenas, J.C. Chaparro Auza, G.A. Chaves-Portilla, G. Chávez, L.A. Coloma, C.F. Cortez-Fernandez, E.A. Courtois, J. Culebras, I. De la Riva, V. Diaz, L.C. Elizondo Lara, R. Ernst, S.V. Flechas, T. Foch, A. Fouquet, C.Z. García Méndez, J. E. García-Pérez, D.A. Gómez-Hoyos, S.C. Gomides, J. Guerrel, B. Gratwicke, J.M. Guayasamin, E. Griffith, V. Herrera-Alva, R. Ibáñez, C.I. Idrovo, A. Jiménez Monge, R.F. Jorge, A. Jung, B. Klocke, M. Lampo, E. Lehr, C.H.R. Lewis, E.D. Lindquist, Y.R. López-Perilla, G. Mazepa, G.F. Medina-Rangel, A. Merino Viteri, K. Mulder, M. Pacheco-Suarez, A. Pereira-Muñoz, J.L. Pérez-González, M.A. Pinto Erazo, A.G. Pisso Florez, M. Ponce, V. Poole, A.B. Quezada Riera, A.J. Quiroz, M. Quiroz-Espinoza, A. Ramírez Guerra, J.P. Ramírez, S. Reichle, H. Reizine, M. Rivera-Correa, B. Roca-Rey Ross, A. Rocha-Usuga, M.T. Rodrigues, S. Rojas Montaño, D.C. Rößler, L.A. Rueda Solano, C. Señaris, A. Shepack, F.R. Siavichay Pesántez, A. Sorokin, A. Terán-Valdez, G. Torres-Ccasani, P.C. Tovar-Siso, L.M. Valencia, D.A. Velásquez-Trujillo, M. Veith, P.J. Venegas, J. Villalba-Fuentes, R. von May, J.F. Webster Bernal & E. La Marca (2023): Ongoing harlequin toad declines suggest the amphibian extinction crisis is still an emergency. — Communications Earth and Environment, 4, 412.

First release trial of Atelopus limosus shows that animals rapidly recover a wild-type skin microbiome.

In 2017, Virginia Tech PhD students Angie Estrada and Daniel Medina conducted the first release trial of captive-bred Limosa Harlequin frogs at the Mamoni Valley Preserve. Their study aimed to closely observe how 1-year-old captive-bred animals would transition from captive conditions back into the wild. To soften the blow of the changing conditions, and to allow the researchers to capture the frogs again, they designed 30 square shaped mesocosms from plastic mesh. In reintroduction biology placing animals in a temporary field enclosure prior to release is known as a soft release. They filled the bottom layer with leaf litter collected from the forest floor that was rich in leaf-litter invertebrates, a diet quite different from the crickets and fruit-flies they are usually fed by staff at the Panama Amphibian Rescue and Conservation Center. Each mesocosm housed a single animal that was monitored daily  for a month and weighed and swabbed weekly.

It is known that captivity can alter skin microbiomes of amphibians and other captive animals, and that this is an important component of amphibian immune defenses. This study found that wild and captive Atelopus limosus had very different microbiomes, but that after a month living in mesocosms, the skin microbiome had rapidly changed to resemble the microbiome of wild individuals. One concern about bringing animals into captivity for prolonged periods is that animals might lose symbiotic microbes that help them to survive in the wild, which might reduce the fitness of captive-bred animals, but this study found that the skin microbiome was rapidly rewilded.

The mesocosms were a useful tool that protected the animals from larger predators, though one was killed by army ants. Female animals lost body condition more rapidly than males, but at the end of the trial their condition resembled that of wild-caught animals. About 15% of the animals became infected with the amphibian chytrid fungus in the first month compared to 13-27% Bd prevalence in wild amphibian community.

Estrada, A., Medina, D; Gratwicke, B, Ibáñez, R, Belden, L (2022) Body condition, skin bacterial communities and disease status: Insights from the first release trial of the Limosa harlequin frog, Atelopus limosus. Proceedings of the Royal Society B.

Spindly leg syndrome is reduced by increasing calcium hardness of water used to rear tadpoles

Atelopus varius metamorph with spindly leg (left) and without spindly leg (right)

Rearing frogs in captivity has its own unique challenges, one problem that has been a persistent issue in the Panama Amphibian Rescue and Conservation Project is spindly leg syndrome (SLS). This common musculoskeletal disease is mostly associated with captive amphibian breeding. SLS is a condition where legs of newly metamorphed amphibians, with otherwise healthy and typical development, are poorly developed and cannot support the weight or newly metamorphed froglets. Ultimately, SLS leads to death as the animal is unable to move or feed themselves. A brief review online will reveal a host of theories and potential remedies for the condition ranging from parental nutrition to water quality and dietary supplements, but there are very few replicated peer-reviewed experiments identifying the cause of this disease.

Elliott Lassiter and Orlando Garcés with the experimental rearing setup

As an intern with the Panama Amphibian Rescue and Conservation Project I teamed up with Orlando Garcés a graduate of the University of Panama and employee of the project to conduct an experiment primarily funded by the Morris Animal Foundation. We had observed that SLS was most prevalent in water that did not have any supplementary calcium and we knew that incoming water to our facility was very soft (lacking in calcium hardness). Bone growth is the symptom of SLS, therefore, we decided to look at the principle minerals affecting bone growth: calcium and phosphate. Tadpoles can gain calcium through their diet but they absorb about 70% of their calcium from the water through their gills and skin. The collected calcium is then stored in endolymphatic sacs in their heads and used during metamorphosis when tadpoles’ skeleton turns from cartilage into bone and limbs begin to grow.

We took 600 Atelopus varius tadpoles and divided them into three calcium treatments (low, medium, high) and then divided those into two groups one with added phosphate and one without added phosphate.  We monitored our tadpoles until they metamorphosed, at which point we looked at their legs and body posture to determine whether or not they had SLS. We found that calcium supplementation drastically increased survivorship overall and that the medium and high calcium groups had less SLS than the low calcium groups. Addition of phosphate also decreased the prevalence of SLS in low calcium treatment.

Based on the results of this study we were able to determine that SLS in harlequin frogs, is linked to an imbalance in calcium and phosphate homeostasis. Therefore, our current husbandry recommendation to reduce SLS in frogs and toads is to consider checking water hardness to determine if it is too soft. We also advise against over feeding tadpoles which has been shown to cause an increase in SLS prevalence in another experiment. We hope that our findings can guide future SLS research and help to lower the prevalence of SLS in captive amphibians, improving animal welfare. This research will help to improve the long-term sustainability of captive populations while researching solutions for the amphibian chytrid fungus and eventual reintroduction of these frogs back into the wild.

Lassiter, E., Garcés, O., Higgins, K., Baitchman, E., Evans, M., Guerrel, J., Klaphake, E., Snellgrove, D., Ibáñez, R. and Gratwicke, B., 2020. Spindly leg syndrome in Atelopus varius is linked to environmental calcium and phosphate availabilityPloS one15(6), p.e0235285.

By Elliot Lassiter and Orlando Garcés

Update on the conservation status of Harlequin Frogs in Panama

On May 30, 2019 a special issue of the Journal Biological Conservation entitled ‘Amphibian conservation in the Anthropocene: Progress and challenges‘ Edited by Vincent Devictor, Evan Grant, Erin Muths, Benedikt Schmidt, Silviu Petrovan was published. The focus of this issue is on examples of potential solutions to the amphibian crisis that are directly relevant to, and integrated with conservation management actions.

The issue features a case study on Atelopus in Panama, updating the known historical distribution records and modeling potentially suitable habitat (below).

The paper also updates the IUCN conservation status for each Panamanian Atelopus species and the status of each of these species in captive populations, with commentary on the potential use of the captive population in research to find solutions that may be useful in restoring wild populations.

Atelopus conservation status in Panama 2019

Lewis CHR., Richards-Zawacki CL., Ibáñez R., Luedtke J., Voyles J., Houser P., Gratwicke B. 2019 Conserving Panamanian harlequin frogs by integrating captive-breeding and research programs. Biol. Conserv. 236, 180–187. (doi:10.1016/J.BIOCON.2019.05.029)