The Bad and the Bizarre: Chytridiomycosis and the Mass Extinction of Amphibians
This is a story of the deadly amphibian fungus, in layman’s terms for the common frog-lover.
Our story begins with the bizarre, as most good stories do. It’s the 1930s, and two South African researchers (mad scientists?) are in their lab trying to figure out an easy way to determine human pregnancy before a woman has a visible baby bump— yes, there existed a time before you could just pee on a magic stick. Naturally, they’ve got a jar of pregnant lady pee and a couple of South African Xenopus frogs, because what kind of self respecting researcher doesn’t keep these vital materials in their lab? I certainly do, and I know you do too, even if you won’t admit it.
For reasons unknown to me, the next thing these researchers decide to do is inject these frogs with the pregnant lady pee and miraculously discover the first way of testing for pregnancy in the modern world. It turns out that the Xenopus frog will ovulate if injected with pregnant lady pee (it won’t ovulate if the woman isn’t pregnant), and that the world in the mid-1900s was positively thrilled to have a strange, wildly inconvenient, and entirely unethical way of testing for pregnancy. Believe it or not, these urine-infused frogs were actually quite good at their job; the tests were remarkably accurate.
The next thing the frogs knew, they were being scooped up from their native South Africa and exported around the world to be serve as vessels for human pee and windows into the enigmatic female reproductive system.
Now we move onto the bad of our story. Fast forward to today: we’re looking at a mass extinction of amphibians worldwide, courtesy of a fungal disease called Chytridiomycosis, and something smells fishy. Or, more accurately, like pregnant lady and Xenopus frogs. Many scientists now believe that the Xenopus frog might have been the first vector of Chytridiomycosis, and that the worldwide frog exodus from Africa in the 1940s-60s for pregnancy testing initiated the spread of the fungus. How does this disease work, why should you care, and how the hell do you pronounce Chytridiomycosis (so that you can tell your friends about it at parties, and impress your date)? Most people can’t pronounce it either, so it’s commonly called amphibian chytrid fungus disease, or just Bd, a shorthand for the name of the fungal species. As for the other two questions, keep reading below!
How does Chytridiomycosis work?
Fungi reproduce through zoospores, which are basically just tiny fungus babies that can swim through water using whip-like tails called flagellum. As this zoospore is swimming through a pond, it might, naturally, encounter a frog. Frogs have permeable skin, which means water moves between the frog and its environment— frogs actually drink through their skin, and can breathe underwater by absorbing dissolved oxygen. Upon encountering a frog, the zoospore will cross through the frog’s permeable skin and establish a sporanguim, which is a fungal reproductive structure that produces more zoospores. The fungus can then spread through the frog’s body in as short as a week, infecting it with Chytridiomycosis.
Chytridiomycosis carries a host of unpleasant symptoms, ranging from lethargy to convulsions, but what normally ends up killing the frog is that it thickens the frog’s otherwise permeable skin. In losing its permeability, the skin can no longer absorb water, oxygen, and nutrients, nor expel bodily toxins— the frog cannot drink or breathe. What’s crazy about Chytridiomycosis is how little we know about how the disease spreads or how to deal with it on a global scale, especially since its range is growing due to climate change. One of the mysteries of the disease is that the zoospores cannot move more than 2cm before becoming inactive; this means that their ability to travel and infect new frogs is very limited. Chytridiomycosis infects an estimated 30% of amphibian species worldwide, and yet scientists are struggling to find a feasible way to stop its spread, and quite possibly never will due to the nature of the disease.
Why should you care?
Because frogs are cool and important. The mass extinction of amphibians is a poorly understood threat to biodiversity worldwide. Amphibians play a crucial role in global ecosystems, and the loss of a single species can have rippling effects throughout an entire food web. We are facing quite possibly the greatest conservation challenge in human history, with one out of every three amphibians worldwide threatened by extinction and no clear solution in sight. The number of species at risk runs up to the thousands. The media tends to highlight the more drastic and eye-catching stories of biodiversity loss— the posterchild of global warming is the cuddly polar bear on a melting iceberg— but our biggest hurdle in the race against extinction, and where we should be focusing more attention, comes from the smallest members of our vertebrate family: amphibians.