“Red Eyed Tree Frog (Agalychnis callidryas)” by Brian Gatwicke is licensed under CC 2.0
Though Kermit the Frog may sing of his aesthetic woes, amphibians are facing far greater problems globally. Emergent infectious diseases are wreaking havoc on amphibian populations, namely in Australia and Central and South America due to a new chytrid fungus discovered in 1998. It is suspected that this newly recognized fungal disease is the root of recently dropping numbers of amphibians and increasing frequency of extinctions.
The new chytrid fungus was discovered following the mass death of amphibians in Australia from 1993 to 1998 and isolated as a probable source of the population decline. Dr. Peter Daszak of University of Georgia published extensive research in his paper Emerging Infectious Diseases and Amphibian Population Declines in 1999 indicating that the chytrid, found to infect mostly tadpoles, was the first of its kind – no other chytrids before it caused disease in any vertebrate species. The presence of the fungus in amphibians is evidenced by a number of symptoms, including abnormal posture, lethargy and skin lesions.
What’s most striking about these findings – other than its effect on amphibian numbers – is that this chytrid was found on two different continents at the same time: Australia and Central America. Further research showed that the amphibian-infecting chytrids in both places are very likely the same species.
How could an unknown species pop up in two continents at once? Scientists suspect that although the identification of the chytrid is new, but the fungus itself may not be. Another possibility is that the chytrid has only recently evolved to cause disease in amphibians and was formerly less harmful. It has also been proposed that the fungus evolved in one continent and was carried by humans to the other, where it very quickly gained prevalence.
It’s important to note that the chytrid fungus has not been found in every location where amphibian extinction rates have surged. Dr. John Alroy of Macquarie University studied this in his paper Current extinction rates in reptiles and amphibians. “I think the real situation is hard to figure out,” Dr. Alroy explains. “The problem is that Bd [the chytrid fungus] has not been strongly implicated in mass deaths in Brazil, Madagascar, and New Guinea . . . Something else could cause those declines, most likely habitat loss.” Another possibility, as Dr. Alroy suspects, is that the chytrid fungus simply hasn’t been identified in those regions yet.
The chytrid fungus has been known thus far to have infected 38 species of amphibians belonging to 12 families. A disease that is able to infect so many species is bad news for amphibians the world over. At this point, the chytrid fungus has impacted species that originated from Europe, Africa, Madagascar, the Americas, and Oceania and has the potential to not only spread to these locations, but to dominate and, as a result, to decimate the amphibian populations in each of these locations. Disappearing amphibians open up gaps in food webs that cannot always be filled by other species. The result is a ripple effect throughout the entirety of the network of living things. “They’re the first animal that kids can recognize after their teddy bear,” Andrew P. Dobson of Princeton University reflects on the current outlook for frogs. “And for most of the kids, looking in those books is the only chance they’re get to see one now.”
With amphibian extinctions being so widespread, not all extinctions can be attributed to the chytrid fungus. However, some scientists blame the harmful effects of increased levels UV-B rays due to ozone depletion, while others point to chemical pollution, climate change, and habitat destruction playing roles in the amphibians’ declining numbers. Habitat destruction is imminently harmful, as amphibians are crowded into smaller places, in which it is easier to spread disease. These factors must be playing a large role in areas that have not been affected by the chytrid fungus.
Amphibians in Central America and Australia, or anywhere for that matter, may not seem significant to the average person. However, amphibians are uniquely indicative of the state of the environment. Because they breathe and soak up water through their skin and they live both on land and in water in different phases of life, their health is tightly intertwined with that of the habitat they live in. Dying-out amphibians signify impending ecological disaster for the rest of the living if circumstances do not drastically change. With 3.1% of frog species already extinct and another 6.9% of species expected to follow suit, there’s real reason for concern, but the question of how to help amphibians survive and effectively combat the chytrid fungus remains.
Daszak, Andrew P., Berger, L., Cunningham, A. A., Hyatt, A. D., Green, D. E., & Speare, R. (1999). Emerging infectious diseases and amphibian population declines. Emerging Infectious Diseases, 5(6), 735–748.
Alroy, John. (2015). Current extinction rates of reptiles and amphibians. Proceedings of the National Academy of Sciences, 13003-13008.