Adaptation

Q: You received a $730,000 National Science Foundation grant to study the maternal and eggshell microbiome of striped plateau lizards. What are you hoping to discover?
A: Our hypothesis is that maternal microbes coat the lizards’ eggs and protect them from fungal pathogens in the nest environment. In reptiles, parental care is rare; is there a way for the mother to protect her eggs in her absence? We developed this research based on an anecdotal observation. When incubating eggs in the lab, I’ve found that if an egg is laid by the female, it has a very high hatch success, but if it’s surgically removed from the mother, it’s less likely to be successful. Why is that? It was my colleague Mark Martin who had the idea of cloacal microbes—it really was one of those hallway conversations with him that led to this work. Since then, we’ve learned that when an egg is laid naturally through the cloaca—the tube that’s the shared end of the digestive and reproductive tracts—it has more bacteria compared to the surgically removed eggs. More bacteria resulted in less fungus, and more hatch success. These results are the focus of a recent open-access publication in Animal Microbiome that includes my wonderful technician, Marie Bunker, as lead author; two undergraduate students, Grace Elliott and Helena Heyer-Gray; and two colleagues, Mark Martin and Betsy Arnold (from University of Arizona) as co-authors. My current research student McKenna Boulet is trying to figure out which bacteria are affecting which fungi, and what the underlying mechanism might be.

Q: What’s the broader significance of all this?
A: It’s multifold. We have good support for the evolution of egg-protective cloacal microbes in one lizard species. But this mechanism of egg-protection could potentially be very wide-spread among oviparous, or egg-laying, animals. If so, it will open up new ways to think about the role of microbes on their hosts. The field of microbial ecology is rapidly advancing, and we’re learning so much about host-microbe coevolutionary relationships. Since I’m trained as a behavioral ecologist, I’m very interested in investigating how my microbial work intersects with theory about the evolution of parental care—or lack thereof—and of female sexual signaling. For instance, might females advertise their high quality, egg-protective microbiome to potential mates? It’s also critical to our field that we’re studying a diversity of host species, environmental pressures, and adaptations—and, so far, lizards tend to be underrepresented in microbial ecology. So even the basic descriptive components of our work are important. 

Q: Is there conceivably any relevance to humans?
A: Yes. Since we’re looking at antifungal properties of cloacal bacteria, our work could potentially identify new antifungal agents. That aspect isn’t what drives my intellectually curiosity, but it’s the only time in my career when my research could have direct impacts on human health.

Q: How does one measure bacteria and fungus on lizard eggs, anyway?
A: It’s actually pretty fun. To catch the lizards, we use a lasso slipknot—a fishing line at the end of an extendable fishing pole—and we get a loop around the lizards’ neck and flick up. Then we pull them out of the loop and take a swab and gently twirl it around in the cloaca to collect a microbial sample. While the lizard is in hand, we also take basic measurements—sex, mass, length—and one of our undergraduates, Alexi Ebersole, takes a little snip of their tail tissue, so we can learn about their diets using stable isotope analyses. Then we put a small dab of paint on their back and release them. Then in the lab, we can culture the material from the swab in a petri dish, see what grows, isolate it, extract and sequence the DNA, and use databases to find its identity. We also use high-throughput sequencing to identify all the microbes in the sample; this requires advanced bioinformatics to give us measures of microbial diversity and composition.

Q: Presumably the paint helps you keep track of them?
A: Right. Some of the work I was doing this summer was trying to understand how much time the eggs incubate in the nest before hatching. When these lizards lay their eggs, they dig a little burrow, lay their eggs, camouflage the site, and then leave. If you didn’t see the mother making the nest, you would never know it was there. I want to find populations where the eggs are in the soil a relatively short time, and ones where they’re in the soil a relatively long time—factors that may put different selective pressures on the cloacal microbiome of the lizards. And that’s really hard to find out—it’s very labor-intensive. I spent quite a bit of time this summer sticking little transmitters on lizards’ backs and following them with a receiver until we found one nest. We have a cage around it now, and we’re checking it daily for hatchlings to emerge. 

Q: Your current research has kept you relatively close to campus, including beaches on and around Chambers Bay, after the pandemic caused you to relocate your study site from Arizona.
A: That’s right. We normally work in the Chiricahua Mountains, in the Sky Islands of southeast Arizona. The region’s amazing—about 5,500 feet elevation, oak scrub habitat, 40 miles from Mexico and 10 miles west of New Mexico, incredibly high biodiversity. The main species I study there is the striped plateau lizard. When I couldn’t get to Arizona in the summer of 2020, we focused on the western fence lizard, which ranges from Baja California up to Washington State, and began to investigate how the cloacal microbial community varies across populations, including high and low elevation sites.

Q: How has that transition gone?
A: We were starting from scratch, and there’s a lot of legwork involved in starting new populations, but I had three students lined up and a wonderful lab technician, and they came to it with great ideas. So we take a team mentality to our field work—we call ourselves Team Sceloporus, the genus name of our lizards—and while we’re out in the field collecting microbial samples, we simultaneously address other questions. For instance, Alexi’s interested in how species adapt to local conditions—on the beach, the lizards live on driftwood, and at the higher-elevation site, they’re living on rocks in dry creek beds. He found really interesting morphological differences that suggest the lizards can adapt to their local environment. And now we’re also comparing the role of marine-based food resources on the diets of lizard populations across the Puget Sound using those tail tissue samples I mentioned.

Q: How integral are these students to your work?
A: It’s really a mutual collaboration, and I’ve been so fortunate to have amazing students working with me—so many of the questions we’re investigating are student-driven. Usually when I first meet with students interested in research opportunities, I tell them my aims for the upcoming summer and ask them what they’re most interested in contributing to. But especially when we’re doing stuff that’s a little bit off from my main expertise, we work together, but they take ownership of the project. It’s really one of the most rewarding parts of my job.