Erin Sauer: toads, fevers and finding ecology

Dr Erin Sauer in Iceland (with puffin.)
Dr Erin Sauer in Iceland (with puffin.)

Dr. Erin L. Sauer is a postdoctoral researcher at the University of Wisconsin – Madison in the Forest and Wildlife Ecology Department. Her research focuses on understanding how environmental pressures and animal behaviour shape host-parasite interactions, and she recently published a paper showing that behavioural fever reduces ranaviral infection in toads

What’s your paper about?

Southern toad in the green. Photo credit Jeremy Cohen
Southern toad in the green. Photo credit Jeremy Cohen

The ability of wildlife populations to rapidly respond to pathogens is critical in reducing the impacts of disease outbreaks. Unlike endotherms, ectotherms cannot internally adjust their body temperatures, and must behaviourally thermoregulate to modify their body temperatures and induce a fever when they’re sick. But we have limited information regarding the ability of ectothermic wildlife to resist diseases by altering their behaviour. We experimentally examined the effect of host behaviour on ranaviral infections, which affect at least 175 species of ectothermic vertebrates including many declining amphibian species. Using thermal gradients, we measured temperature preferences of Southern toads (Anaxyrus terrestris) both before and after viral exposure and found that toads typically moved to warmer areas during the first two days after viral exposure. Additionally, we wanted to determine if behavioural fever was effective at reducing ranaviral loads because of heat alone or some combination of heat and host response, such as an immunological response. Interestingly, we found that a relative increase in temperature preference was more predictive of reduced ranaviral loads that absolute temperature. Therefore, behavioural fever may reduce ranaviral infection by some combination of heat and increased immune efficiency and not by simply heat killing the virus.

How did you come up with the idea for it?

Southern toad. Photo credit: Jeremy Cohen
Southern toad. Photo credit: Jeremy Cohen

When I started my PhD, I was initially interested in determining if amphibians would use behavioural fever to fight infections from Batrachochytrium dendrobatidis (Bd), a fungal pathogen that is responsible for declines in hundreds amphibian species worldwide. There were a couple of field studies that showed that amphibians preferring warmer temperatures were less likely to be infected with Bd. However, there was some debate over whether the field patterns were driven by fever or by survival only among individuals that had always preferred warm microhabitats. We tested for behavioural fever in response to Bd exposure in five species of amphibians and found no evidence for fever. Despite those results, I wondered if amphibians do not make use of behavioural fever at all or whether they would behaviourally thermoregulate in response to a virus. Viral pathogens are commonly associated with fever and ranavirus is a pathogen of conservation concern for amphibian populations worldwide. So, we repeated the Bd fever experiment with Southern toads and ranavirus.

Did you have any problems setting up the experiment and gathering your data?

Dr. Sauer’s thermal gradient setup.
Dr. Sauer’s thermal gradient setup.

Setting up the behavioural fever experiments and gathering data was very challenging. I spent my first semester of graduate school designing and constructing thermal gradients that would work with amphibians. The majority of research on behavioural thermoregulation has been conducted on species that are either fully aquatic or far less sensitive to moisture than amphibians. We needed to design terrestrial thermal gradients that could maintain both a wide range of temperatures as well as consistent, high humidity and be used in relatively long experiments where we were measuring amphibian behaviour for more than a month. It took a lot of creativity, duct tape, and many trips to the hardware store but eventually I designed something that worked and I published those methods in the Journal of Thermal Biology.

How did you get involved in ecology?

I’ve met a lot of ecologists who were heavily exposed to science or nature as kids and always knew that they wanted to be a scientist. My story is a little bit different. I grew up in a densely populated, heavily urbanised part of South Florida. I had never even heard the word ‘ecology’ or met an ecologist until I started my undergraduate degree. I would not have been able to go outside and correctly identify more than a couple common urban species until I was in my twenties! But I was good at science and math in grade school so I, like many other first-generation college students, figured that meant I should go into medicine. When I got to university, I signed up for a pre-med major, but after taking an ecology and evolution course with an incredible instructor, I decided I wanted to be an ecologist, changed my major and never looked back. I’m telling this story because for some of us, our lack of institutional knowledge can make us feel like outsiders. You hear stories from your peers about their early experiences and you can’t help but compare them to your own lack of experience and feel like you don’t belong. It’s hard to get past that feeling and sometimes I still feel that way. But we all belong and our diverse perspectives benefit science.

What do you do in your spare time?

I got into bird watching a few years ago and now I’m pretty obsessed. I recently started a chapter of the Feminist Bird Club in Madison, Wisconsin. We’re a bird watching group dedicated to promoting diversity in birding and providing a safe opportunity to connect with the natural world while fundraising to protect the rights of LGBTQIA+ folks, women, and people of colour. The club, founded by Molly Adams in 2016, has a handful of chapters in the U.S. and one in the Netherlands. I highly recommend checking out our fundraising efforts and/or joining a chapter for a walk if you have to opportunity. The group is a wonderful combination of birding, fun nature hikes, science communication, and social justice. (link:

You can read the paper in full here or the free plain language summary here.

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