As disease researchers, our ears perk up when we hear about a wildlife disease-related decline. Where did it happen and why? How many species were affected? Is there a chance that the disease will continue to spread?
These are of course very important questions to address. We need to move quickly when a decline is happening if we want to prevent a large amount of damage to wildlife and ecosystems. If we let wildlife disease run wild, it could lead to local extinctions or irreversible effects on ecosystems. But is researching declines the best way to prevent future ones?
Amphibian chytridiomycosis is a skin disease caused by the fungal pathogen Batrachochytrium dendrobatidis (Bd). Dramatic chytridiomycosis-related declines were reported from around the world starting in the late 1990s. Bd researchers have paid a lot of attention to certain areas that saw the largest declines: Australia, Central America, and the Sierra Nevada region of California. In these areas, Bd drove some frog species to the brink of extinction. The loss of frogs has huge impacts on ecosystems, because frogs serve many keystone functions: they connect nutrient cycles, stabilize the food chain, and keep the ecosystem healthy.
Researchers began to ask why these regions were so susceptible to disease, and where else we might see similar declines. A massive effort began of tracking Bd around the world. Luckily, detecting Bd is pretty easy and non-invasive: you only have to run a cotton swab over a frog’s stomach, hands, feet, and legs to collect skin cells, then the frog can be released. Back in the lab, you test the swab to see if it contains Bd’s DNA. The ease of detecting Bd has led to wide-spread surveillance efforts. As a result, we now know where Bd is: virtually everywhere!
Even though the fungus is more or less everywhere we look, the research community is still very focused on places declines have happened: Australia, Central America, and California. But is this the best strategy? Maybe we can actually learn more by focusing on Bd cold spots, or places where Bd exists but declines are not happening. The key point here is that the presence of a pathogen does not equal the presence of disease.
The goal of my postdoctoral research is to figure out why some frog populations are able to resist chytridiomycosis in the presence of Bd. A very interesting but confusing pattern that has come out of widespread Bd surveillance is that some populations within a single species appear to be very susceptible (they get very sick and maybe even die) while other ones seem to be resistant (they don’t usually get sick and they survive). By studying California frog populations that vary in their susceptibility to Bd, I hope to identify natural variation that can help frogs fight off and survive future Bd infections. For example, if there is a gene or a set of genes that allow frogs to survive, we could use these genes to screen wild populations and set priorities for where to focus our disease prevention efforts.
By studying disease cold spots, we may actually learn more about why disease happens (or doesn’t happen) in the first place. This makes me wonder if other fields could also change the way they ask research questions to really get the information they want. Can you think of any examples? Let me know in the comments below!