Amphibians around the world are dying, and a particularly nasty fungus is playing a major role.
A recent study published in Science confirms that the chytrid fungus (Batrachochytrium dendrobatidis) is causing catastrophic loss to biodiversity through declines in species populations and in some cases, extinction. Some are calling it an amphibian apocalypse.
Michel Ohmer is a postdoctoral researcher at the Richards-Zawacki Lab at the University of Pittsburgh, where scientists study amphibian ecology and conservation. Veronica Saenz is a Ph.D. student at Pitt who, like Ohmer, is working in the field on the fungus. The Allegheny Front’s Kara Holsopple spoke with them about how chytrid fungus is impacting species.
LISTEN to Kara Holsopple’s interview with Veronica Saenz and Michel Ohmer
KARA HOLSOPPLE: Veronica, What does it do to the species that it infects?
VERONICA SAENZ: The chytrid fungus affects the amphibian skin, and the skin is really important in amphibians because they breathe through the skin, and ions are transported from the water to the skin.
MICHEL OHMER: It’s like electrolyte loss in humans. You know, if you’re running, you need to drink Powerade, or something like that afterwards. So if amphibians’ skin is damaged by this fungus, they can lose a lot of electrolytes through their skin, or various ions, and that is what can cause a lot of disruption to their bodily functions.
SAENZ: Eventually it causes cardiac arrest. It has caused massive declines. More than 500 species have declined, and many of them have gone extinct. It’s caused the worst declines in vertebrates.
HOLSOPPLE: So how has it spread and over how many years.
OHMER: The greatest amphibian declines occurred in the 1980s, and that’s when there were many researchers around the globe trying to figure out what was causing these declines. Later in 1998, it was discovered that it was this fungus, Bd for short. This fungus was discovered concurrently in the United States and in Australia. Recently there’s actually been a number of papers that have come out to demonstrate that the pathogen originated in Asia, and likely was spread around the world via the pet trade, and the food trade. As a result of these trades, invasive species have come into various new locations around the world, and they’re able to carry this fungus, and that impacts the native populations of amphibians.
HOLSOPPLE: Can a frog or an amphibian carry the fungus, and not be infected itself?
SAENZ: So there are different species of frogs, and each species has its own susceptibility. Some of them are really susceptible to the fungus, and they will die pretty fast. Other species carry the fungus, but they are not affected by it. They are vectors of the disease, and that means that they will transport the disease to other animals, or to the water. Bd lives in the water, and in any moist environment. It has even been detected like in crayfish–basically anything that’s pretty moist and has keratin might carry the fungus.
HOLSOPPLE: Michel, why has it been so rampant?
OHMER: Well, because the fungus has a recent origin from Asia, it has spread and ended up in populations of amphibians that were naive to the fungus, especially in places like Central America and eastern Australia. These populations had never experienced the fungus before. They didn’t evolve with this pathogen, and so it caused a lot of declines, likely because they didn’t have any resistance to the pathogen. Also, as Veronica was saying, it lives in moist soil and in the water, so it’s easily spread from one pond to the next. Even humans can carry the fungus on the soles of their boots, if they’re moving from one wetland to another.
HOLSOPPLE: Does it impact local species?
OHMER: Chytrid fungus is found in Pennsylvania. We’ve been studying the fungus at the Pymatuning Lab of Ecology, which is the University of Pittsburgh’s field station, and we found really high prevalences of this pathogen at the ponds around the field station. We do see amphibians dying from the fungus, but at this point, they’re in a little bit of a homeostasis, where the host and the pathogen are coexisting. It’s called an enzootic phase. It’s no longer an epidemic, and this is really good news, until the environment shifts. So for example, with climate change, we may see more epidemics happening, because the environment has changed.
HOLSOPPLE: Because it’s getting warmer or wetter? We know that that’s a possibility in Pennsylvania.
OHMER: Yes, so in Pennsylvania, it’s going to get warmer and wetter. This might be good for some species of amphibian, but for other species that prefer cooler temperatures, they may actually become more susceptible to the pathogen because their immune system doesn’t work as well at warmer temperatures.
SAENZ: In the East, especially coming from over-wintering in the spring, they get high infection loads, and then they could clear the infection in the summer. That’s a general pattern that we have seen here in Pennsylvania, where a fungus does better at cooler conditions.
OHMER: It’s likely that certain species, in particular, chorus frogs, may have declined as a result of the chytrid fungus, and also leopard frogs, particularly in the northern parts of their range, have also likely declined due to the chytrid fungus.
HOLSOPPLE: Is there anything that can be done to stop it or slow it?
OHMER: I think at this point it’s very difficult to control the fungus in nature. There are some things that can be done to try to modify habitat. For example, in eastern Australia, it’s been found that after hurricanes, certain streams become sunnier. Amphibians are able to clear themselves of the fungus because they can elevate their body temperature by basking. So it may be possible to modify habitats a little bit to benefit the amphibian over the fungus.
Also, it’s very important that we stop the continued trade of amphibians, and in particular, avoid the introduction of another fungal pathogen that’s been recently discovered in Europe. Batrachochytrium salamandrivorans (Bsal) hasn’t made its way to North America yet, but North America has the greatest diversity of salamanders of anywhere in the world. It’s really important that we don’t have this new fungus invade North America, because we don’t know what will happen to our populations here.
Even local people can help stop the spread of this fungus. You can clean your boots between wetlands. You can clean your fishing gear and your waders, your kayaks. Let them dry out before you then move on to another pond.
That’s important, because there are actually different strains of the fungus, and we don’t want to continue to spread these different strains around, which may have different variances on how strong or effective they are at hurting amphibians.
SAENZ: It’s really hard to get rid of the fungus, but one thing that is good is that some amphibians are actually developing some kind of immune defense towards the fungus, and that’s a kind of hope for us, for more survival.
HOLSOPPLE: Chytrid fungus, even though we’ve seen how deadly it is, is just one threat to amphibians. What else has been contributing to population declines?
SAENZ: Climate change, and any change driven by humans. Other diseases have also been causing declines and pollution.
OHMER: I guess I would just add that we’ve also seen that a number of these stressors that are causing declines of amphibians are actually working synergistically. Things like pollution can impact the immune function of amphibians. Climate change can affect the thermal environment that amphibians live in, as well as habitat loss. So if you lose tree cover, it can really change the micro-habitat, that’s what we call it. So amphibians are really being affected on all fronts in terms of the number of things that are likely leading to their declines.