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Killer Chytrid

Killer Chytrid

Our history and future are both inextricably linked to that of amphibians. As humans negotiate a path through the minefield of climate change, young women such as the author are the torch bearers who will point us in the direction of survival on a planet that is sending us life-saving signals through messengers such as fungi and quickly-evolving vectors that we must fast learn to read and comprehend.

The Beddome’s bush frog is one among the eight species endemic to India’s Western Ghats that is impacted by the chytrid fungus. Photo: Keerthi Krutha.

I stood overwhelmed with joy at my first sighting of the rare, elusive and endangered pignose frog Nasikabatrachus sahyadrensis. It resembled a black ping-pong ball, with two tiny eyes with blue irises and an elongated nose. Even though it was one of the most memorable moments of my life, I felt an undercurrent of sadness and fear. In the moment before sampling this particular pig-nosed frog and the thousands of other frogs I had caught over the past few months, all I could think was ‘please don’t be infected by chytridiomycosis’ (pronounced kai-tree-dee-O-my-ko-sis).

Chytridiomycosis is a fungal infection exclusive to amphibians that is caused by the chytrid fungus. This disease has resulted in the extinction of more than 200 species of amphibians across the globe, and has led to the elimination of numerous amphibian populations, driving them to the brink of extinction. Scientists were perplexed in 1997 when the Panamanian golden frog Atelopus zeteki suddenly began to disappear from its pristine forest habitat. In 1998, the fungus was found to be the pathogen for the infection that ultimately caused the extinction of the golden frog.

The mechanism by which the fungus causes the infection is by colonising the skin. Amphibians are heavily dependent on healthy skin for their survival. They are a unique group of organisms that exchange gases and salts with their surroundings through their skin. Any chemical imbalance in their ecosystems affects them drastically and even leads to their deaths. This, thus, makes them the indicator of an ecosystem’s health.

The chytrid fungus disrupts the exchange capacity of an amphibian’s skin. It colonises the skin of the frog, blocking crucial ion-exchange passages, which leads to a heart attack and the death of the animal. The common symptoms and indication of chytridiomycosis in an amphibian population include thickening and sloughing of the skin, bleeding, lethargy, and mass-death incidents.

The WILD Society team, which the author was part of, carried out an extensive rapid sampling effort for the fungus across the Western Ghats. They first reported the fungus from the Harishchandragad fort in Maharashtra. Photo: Gaurav Shirodkar.

The Frog Fungus in India

In spite of having an adverse effect on frog populations across the world, the fungus was first reported from India in 2011, 13 years after its discovery. In 2012, Wildlife Information Liaison Development (WILD) Society began an extensive rapid sampling effort for the fungus across the Western Ghats biodiversity hotspot and in that same year, I joined the project.

The key objectives of the study were to develop a non-destructive sample collection method, an in-country sample analysis protocol involving molecular tools, to understand the distribution of chytrid across the Western Ghats and to map it.

By the beginning of 2013, with support from the USFWS-Amphibians in Decline fund, the INSPIRE programme of the Government of India and the Indian Institute of Science Education and Research (IISER), Pune, we had achieved success in meeting two of the four objectives. All that our team from WILD Society was left to do was to understand the distribution of the fungus and map it. With financial support from the Mohammed Bin Zayed Species Conservation Fund and permissions from the state Forest Departments of Maharashtra, Karnataka, Kerala, Gujarat, Goa and Tamil Nadu, we began our sampling efforts.

Our first report of the fungus was from a population of the endangered and endemic Bombay night frog Nyctibatrachus humayuni from an ancient fortification known as Harishchandragad in the state of Maharashtra. The population was found in one of the numerous rainwater collection pools at the fort. The population displayed the typical symptoms of skin sloughing and bleeding. After these initial results, we conducted surveys in areas outside of Protected Areas and discovered that the fungus is widely distributed across the Western Ghats. The other species on which the fungus is presently known to occur in India include Ghate’s bush frog Raorchestes ghatei, Beddome’s bush frog Raorchestes beddomeii, Amboli bush frog Pseudophilautus amboli, mountain golden-backed frog Indosylvirana montana, black torrent frog Micrixalus saxicola, Günther’s leaping frog Indirana brachytarsus and Matheran leaping frog Indirana leithii. All of these species are endemic to the Western Ghats. Interestingly, the strain of the fungus we discovered in the Western Ghats is presently known to occur only in Asia. This Asian endemic fungal strain is currently known from India, China and Japan. By the end of 2014, we had collected close to 3,000 samples from 60 sites across the Western Ghats, the analysis of which is still underway.

One of the objectives of the study was to develop a non-destructive sample-collection method. Photo: Keerthi Krutha.

Searching for Answers

These discoveries lead us to ask three questions – firstly, if the fungus is so widespread, is it a real threat and if yes, how?; secondly, what is the significance of studying any wildlife disease?; and thirdly, is this a priority in amphibian conservation?

I’ll address the last point first. Every species, be it an amphibian, reptile or a bird, has a role to play in its ecosystem. Studies on understanding the role being played by each species are few, and this aspect of understanding ecosystem services is still in its nascent stage. Studying the service being provided by each species is crucial. Having said that, disease is a natural method of keeping a population in check and pathogens are as much a part of an ecosystem as their hosts. But in today’s day and age, with changing weather patterns due to global warming, diseases are surfacing in ways unknown. This claim may lack substantial evidence but that makes it crucial to study and monitor populations affected with a disease like chytridiomycosis.

Chytridiomycosis is a ticking time bomb. Nobody knows when it might burst unless there is continual monitoring of the affected populations. The species of chytrid affecting frogs Batrachochytrium dendrobatidis has a lifecycle of approximately two weeks and thrives in temperatures ranging from 170C to 250C. In India, the symptoms due to infection by chytrid are not common and there have not been any mass-death incidents reported until now.

The current situation in India screams for answers on the long-term effect of chytrid on affected populations, the relation between weather parameters and the local chytrid strain and lastly, the ecosystem role and services meted out by individual amphibian species. These answers will greatly further the conservation of amphibians, in turn aiding in the maintenance of healthy ecosystems and thus, allowing us humans to survive and thrive in a healthy environment.

A scanning electron micrograph of a frozen intact zoospore and sporangia of the chytrid fungus (above), which has caused the extinction of more than 200 species of amphibians across the globe. Photo Courtesy: Dr. Alex Hyatt/CSIRO/Public Domain.

Author:  Keerthi Krutha, First appeared in: Sanctuary Asia, Vol. XXXVII No. 4, April 2017.

 
 
 

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