For a while now, I've been working/studying with a lab that researched a certain type chytrid fungus. It's a herpetology lab (herpetology: the study of reptiles and amphibians, no one knows why they were lumped together, but they were), and the lab focuses on Bd. That is going to change soon, as I am going to begin studying birds, but I'd like to share a little bit of information I've picked up at my current place of work.
In the vernacular, chytrid fungus is a very old type of fungus, and the species were thought to either be saprobes (they eat dead/decaying stuff) or parasites that live on plants and invertebrate animals. Recently, however, and when I say recent I mean 1999, which in the world of science is very recent, a species was discovered that infected the skin of amphibians. Batrachochytrium dendrobatidis (shortened to Bd) was unusual because it was the only chytrid known that affected vertebrates, amphibians specifically.
This is important because Bd appears to be capable of infecting almost all of the worlds amphibian species. An infection with a large amount of Bd is called chytridiomycosis. This disease causes the skin to become very thick, usually deadly in amphibians because they drink and absorb salts(electrolytes) through their skin, not their mouth. Abnormal levels of electrolytes can cause heart failure. In the lungless salamander, which uses its skin to breathe, chytridiomycosis can cause suffocation.
Since it was discovered, Bd has been found on every continent inhabited by amphibians in both wild and captive species. So far, there is still debate over whether this has been historically present and infecting populations all along and recent environmental changes caused a spike in the disease, or because it was only recently introduced to populations which have no defense.
This is a serious disease and has contributed to the recent global decline of amphibian populations. Other factors include environmental change and pollution, and habitat destruction (always a huge and horrible factor, so we need to work on saving the rain forest!).
Amphibians are critically important to our knowledge of the world around us. They are the best indicator species. An indicator species is a species whose presence/absence/health gives an indication of the health of the ecosystem as a whole. Amphibians are excellent indicators because not only to they live on land and in the water, they also absorb the environment right into their skin: water, salts, toxins, everything in the ecosystem.
Right now, their decline is telling us something very important. Habitats and ecosystems are critically changing. In the United States alone since just 1980, the number of native species suffering in severe population decline has doubled. The current extinction rate of amphibians is calculated to be at least 200 times the normal rate of background extinction.
Amphibians require a plentiful supply of fresh water free from chemicals and microbes to survive. So do humans. Human population growth and climate change are combining to create a situation in which a large and increasing proportion of the human population is denied access to sufficient, clean water. The rapid decline of the world's amphibians is a warning that this most precious of natural resources is under serious threat. Frogs aren't the ones contaminating said resources with chemicals. We are.
We need to wake up and get our shit together.
Sources:
Gagliardo, R., P.Crump , E. Griffith,et al. 2008. The principles of rapid response for amphibian conservation using the programmes in Panama as an example, International Zoo Yearbook 42: 125-135.
Hyatt, A.D., DG Boyle, Olsen V et al. 2007. Diagnostic assays and sampling protocols for the detection of Batrachochytrium dendrobatidis, Diseases of Aquatic Organisms 73: 175–192.
Murray, K.A., L.F. Skerratt, R. Speare, and H. McCallum. 2009. Impact and dynamics of disease in species threatened by the amphibian chytrid fungus, Batrachochytrium dendrobatidis. Conservation Biology:23:1242-52.
Rachowicz, L.J., J. Hero, R.A. Alford, J.W. Taylor, J.A.T. Morgan, V.T. Vrendenberg, J.P. Collins, & C.J. Briggs. 2005. The novel and endemic pathogen hypotheses: Competing explanations for the origin of emerging infectious diseases of wildlife. Conservation Biology 19: 1441-1448.
Skerratt, L.F., L. Berger, R. Speare, S. Cashins, K.R. Mcdonald, A. Phillott, H.Hines, and N. Kenyon. 2007. Spread of chytridiomycosis has caused the rapid global decline and extinction of frogs. EcoHealth 4:125-134.