This is the family tree of BD. It’s basically the same as if you were going to make a family tree but I’ve turned it on its side. So the nodes on the tree are the old times and these tips on the tree are the modern samples that we collected and they’re just color coded by what family group they’re in. So what we call BD is a complicated family, it’s not just one thing. There’s old lineages and there’s young lineages. And some of the things that matter about using genetics to understand a pathogens family tree is that we can understand more about where the pathogen came from and we’ve done, not we as me, but we as scientists have done the exact same thing with COVID spite strains is you use the genetics to trace back where the pathogen likely emerged from and how much it’s changing as it moves.
This is what we did for the BD fungus. And what we found is that BD is on all continents with amphibians. It infects hundreds and hundreds and hundreds of species causing massive declines and die-offs in many of them. We also found that one branch of the tree, this green branch is the most recent. It’s the most widespread. It’s the one that’s moving around the world the most quickly. And it’s also the most deadly. So what it looks like is there were some ancient types of BD that were places in the world, probably for a very long time. Right now it looks like Asia and some parts of South America probably had BD for a very long time, but something changed in the last few 100 years and a new, more deadly version emerged. And that version is what’s moved around the world so quickly.
It’s not that BD by itself is always deadly, but like we see also with human pathogens, deadly forms emerge. And then because of our globalization and because of humans moving, animals around for the food trade, animals around for the pet trade, when those deadly versions emerge, they move around the world a lot more quickly than they used to. So we have a recent emerging deadly pathogen, but how does it kill go frogs? Well, this is a skin micrograph and what you can see is these little circles are all the BD cells that have implanted them in the frog skin.
Now, frogs use their skin to breathe through. They use their skin for osmoregulation. They use their skin for electrolyte balance. So if you have a pathogen that’s literally poking holes in the amphibian skin, it doesn’t end well. And so that’s what’s happening is BD is disrupting how the amphibian skin functions and what we’ve been able to do with the genetic approaches is we’ve been able to identify the actual genes that BD is using to do this so we know what the virulence factors are in the genes at the genetic level. And that gives us all sorts of options for thinking about how might you be able to address these kinds of things. No one’s going to invest billions of dollars in a anti BD vaccine but knowing the genetic basis of the virulence really helps us address the problem. And the other thing we’ve learned from the genetics is that BD is stealth. It hides from the immune system. So the frogs are essentially dying before they’ve even mounted an effective immune response.
So what does learning all of this do for us? Well, the big thing that it does for us is it helps us guide conservation efforts. I work really closely with the national park system. We work really closely with Yosemite National Park and Sequoia Kings National Park where we have some of the last remaining Mountain yellow-legged frog populations that are healthy. And we also work really closely with Panama for their captive breeding and reintroduction program. And so what we do is we use the genetic information we collect to help the park service figure out where it’s okay to move frogs around to, which frogs are related to other frogs, and also to make sure that they’re not moving the fungus around when they move the frogs. So we want to make sure that we’re providing really strong, scientific basis for conservation decisions that are being made.
And we have projects focused on genetic monitoring all over the world because we can also look at the pet trade and see what strains of BD are being moved around, how we can stop that, how we can create antifungal drugs that can target BD. So there’s a lot of frog conservation process around this.
The good news about the frog system in specific, and then I’ll zoom out a little more broadly is that populations are actually beginning to recover. And not only are they beginning to recover but they actually show some signs of adapting to become more resistant to the fungus. And so this is our picture, a little graph of some of the recoveries in Panama. Each one of these lines is a different species and the whole community just absolutely crashed when BD arrived. But now 20 years later, some of those species are starting to recover and we’re seeing the same thing in the Sierra Nevada Mountains here in California. I’m not showing you that pre-crash stage but this is just an example from one of the populations we’ve been monitoring where the frogs are actually slowly beginning to recover.
This is not surprising. If we look at other examples of biodiversity crashes, this one has nothing to do with frogs. This is about a cod fisheries where cod were over-fished and once we’ve removed the threats that humans are imposing on biodiversity, systems often display some resilience. Doesn’t mean they have complete recoveries, but here what I’m showing you is that this whole fishery crashed, in the black line you have the cod themselves, but then you have other species that crashed because that species crashed and you just have a cascading effect. But when you stop overfishing, even though the cod are recovering slowly, the other metrics of the community health start recovering more quickly. Other species start coming back. Some of the functional diversity in the ecosystem starts coming back.
It’s not to say that every time we remove a threat, the system’s going to recover, but the science tells us again and again that if you don’t address the threat, the system is definitely not going to recover. So a lot of what our scientific data are doing are helping managers understand how to best remove the threats. So in the case of the frogs, we’re helping conservation practitioners understand how to best remove the threat of the fungus and best give the frogs a chance of recovery. The other thing that is hopeful in the small story about the frogs is that every time we’ve confronted as a scientific community one of these diseases outbreaks and addressed it, it tightens up the processes that we use as scientists and it means that our response to the next threat is much faster.
We had been working on amphibian declines for a decade before bat white nose syndrome, which some of you may have heard of. It’s a deadly disease that has been affecting bats around the country before that disease emerged. And because we already had a community that was really well positioned to take a multidisciplinary approach to wildlife diseases, the community was able to jump and address that threat much more quickly. So some of the hope that comes in the small story about the frogs is that science does help us identify threats to biodiversity. And it helps us work to remove those threats in an intelligent way. But one of the things that’s very clear to me as a scientist is that a lot of the hope in the stories of biodiversity come from the resilience of life itself. I, as a scientist, contributed data and ideas to help us think about how to remove a threat, but I did not help the frogs recover. I did not help the frogs evolve.
And so what I have come to as a scientist is that as scientists, we need to be deeply engaged in generating fabulous data and sharing it with managers on the ground so the biodiversity conservation can happen in the best way possible, but we can’t only do that. There’s something deeper we need to address. And so what I’d like to do for the second part of our time together is talk about that deeper thing. I personally do not feel as scientists that we can address the threats to biodiversity that are facing the planet if we don’t address the worldview that created them. And I’m very specifically focused on the idea of a worldview here not just the idea of people doing bad things because I don’t think that’s helpful and I don’t think that gets us where we need to go.