And so I’ll just give you a very brief little foray into the world of amphibians here. I don’t know if any of you are amphibian lovers but they are a big branch on the vertebrate tree of life. They’re incredibly diverse. There are amphibians that are smaller than your pinky fingernail and there are amphibians that are as large as I am. There are amphibians that the fathers carry the babies on their back and exhibit parental care. There are amphibians where the mothers swallow the babies and let them undergo metamorphosis in their belly before they puke them back up. So the amphibians are incredibly diverse and they also are real survivors. Amphibians evolved well before the dinosaurs and have survived the last three major extinction events on our planet. And so why amphibians were disappearing at such an alarming rate was an incredible mystery in a biodiversity sciences arena.
We know that current amphibian extinction rates are at least a 100 times higher than we would expect them to be if humans were not involved on the planet. And we can name a lot of usual suspects that are contributing to those elevated extinction rates, climate change, which I know is a big focus in your learning this fall, habitat change, over exploitation in the pet trade and the food industry, introduced species, contaminants, and what I became really interested in is the role of emerging infectious diseases in these biodiversity declines.
At the time, so this was more than 15 years ago, scientists were warning about how emerging infectious disease rates seem to be rising significantly over time. Sitting here in the middle of a pandemic that does not come as a surprise to anyone but 15 years ago, this was already being noticed in other species. And if you think about the degree of globalization we have in our world, it is not surprising that we’re moving diseases around at an unprecedented rate and that those are diseases that don’t only affect humans but they’re diseases that affect agriculturally or ecologically important species, so potato blight, Sudden Oak Death, Hantavirus, even bird conjunctivitis.
There’s an incredible number of diseases of wildlife that are contributing to declines. And the interesting thing is that this is not separate from human activities. This has causes and effects that relate to humans. We’re causing many of these wildlife disease declines because we’re moving diseases around the world at an unprecedented rate, but we’re also affected by them. So sometimes when I give a talk about like frogs dying from a deadly disease, it seems trivial relative to the kinds of challenges that humanity is facing. But I really want to underscore today the reality that we are existing in one planet with one health. So if we decimate the species around us, that does not end well for humans either. So the question of why should we care about impacts on other species is quite obvious when you think about the fact that humans also can’t survive if the trees are being killed, if our foods are being compromised, if wildlife chains of interactions are being disrupted.
So, this is a talk really about amphibians but it relates to humans in two ways. One is directly because as we affect biodiversity, we affect ourselves. And the other is more indirectly and I’ll talk about that towards the end of our time together. So after a few years of research, what we started emerging around the world was that there was a new pathogen that was unknown to science that was killing frogs all over the world and it has a fancy name Batrachochytrium dendrobatidis and I will not say that again we will call it BD for the rest of the talk today. And it’s a fungus… Let me turn the sound off here so you don’t hear the sound of listening to a microscope.
This is an aquatic fungus. You see these little swimmy cells, they’re fungal cells, they have little flagella, little tails so that they can maneuver around in the water. They find frogs, and then they attach to the frog skin, and then they develop into these reproductive bodies that then create more of these little swimmy cells that then go out and affect more frogs. So this was just emerging, this pathogen had just been discovered when I started getting interested in this question. And I started thinking about the systems that I knew best. I had really close friends and collaborators working here in California on the Mountain yellow-legged frogs, which are an iconic species in the Sierra Nevada Mountains and I had really close friends and collaborators working in Panama on this Panamanian golden frog. And both of these species just started tanking. And this was right around the time that something else was tanking.
And the other thing that was tanking was the price of doing science. I had been trained as a geneticist and so I had been thinking about, is there a way that I could use genetic tools to try to understand what’s happening with these extinction events all over the world. And right around that time, the first human genome had been sequenced and the first human genome took 15 years to sequence and nearly $3 billion. And by the time that I had my first faculty job, a human genome could be sequenced in less than $1,000 in less than a day. So there’ve been this massive technological revolution in whether and how we could use genetic tools to ask questions not only about humans, but about other species on the planet as well, because I promise you, no one is going to spend $3 billion to sequence a frog genome but if a frog genome could be sequenced in $1,000 now all of a sudden we can start understanding what’s happening at a genetic level and why this pathogen is killing these frogs around the world.
The other thing that was happening is that we’re now able to sequence DNA from much, much, much smaller amounts of DNA. You used to basically need to sacrifice an entire frog to get enough DNA to do anything with it but now we can have a feather, we can have a snake skin shed, we can have a little bear fur rubbed up against a tree. We can have deer poop. We can have a swab where we took a little skin cells from a frog’s belly. We can even just take water out of a pond and we can use that material to get genetic data and genetic data can then tell us an incredible number of things about the biodiversity declines we’re seeing today.
So I started out wondering if I could help answer some of the big questions about amphibian declines using some of these noninvasive genetic techniques where I swabbed frogs bellies, and then sequence the DNA because that swab has frog DNA on it, but also BD-DNA. So the questions that I set out to answer were things like, where did BD come from? What makes this pathogen so deadly? What makes frog susceptible to this disease? How can our science best inform how we use our conservation dollars in nature? And is there any hope? So I’m not going to take a very deep dive into the science details but I want to give you a few of the answers that came from these explorations because it’s been really like a 20 year mystery that we’ve been involved in a worldwide network of scientists trying to solve. And I’ll just give you a few of the highlights on the science side and then we’ll turn to talk about the implications of what we’ve learned for conservation.