Life Lines by Dr. Dolittle

Sponsored by the American Physiological Society

Exploring how temperature impacts the characteristics of animals

1920_caseymueller-050We are delighted to speak with Dr. Casey Mueller who is currently an Assistant Professor at California State University San Marcos. Dr. Mueller is a member of the Comparative and Evolutionary Physiology section of the American Physiological Society and was scheduled to present her research at the 2020 Experimental Biology conference last month. Unfortunately, the conference was cancelled due to Covid-19. Her researchappears in the May issue of the FASEB Journal. 

As a comparative physiologist, what research questions does your lab explore?

My lab explores concepts that are central to developmental physiology. We focus on phenotypic plasticity, when during development phenotypes are most responsive to the environment, and the immediate and long-term effects of the developmental environment in shaping phenotypes across life history. We work with invertebrates, fishes and amphibians to examine how the environment influences developmental trajectories, energy use, and performance. In particular, my lab focuses on the role of the thermal environment. Temperature is such a pervasive factor in shaping the phenotypes of ectothermic organisms, and with changes in the thermal environment predicted with climate change it has never been more important to understand its impact. We are investigating how these changes might influence development, but also traits and performance in later life stages, as we need to investigate physiological responses across life history to truly understand how a species might be impacted by climate change.

Can you tell us about the Baja California Chorus Frogs and what makes them unique?

The Baja California chorus frog (Pseudacris hypochondriaca), is one of three species in the Pseudacris complex (once considered a single species Pseudacris regilla), which extends down the Pacific coast of North America. This particular species is found from Santa Barbara, CA to Baja California, Mexico. The chorus frog is somewhat unique because they are not demonstrating the same declines seen in many other amphibians around the world. Therefore, they provide an interesting opportunity to examine developmental physiology in a robust species. The species seems to be not very susceptible to fungal infections and, of particular interest to me, it is a thermally tolerant species. My lab and others have shown that embryos able to develop successfully between 8°C and 30°C, and tadpoles between 0°C and 33°C, and the adults also tolerate a range of temperatures. Basically, I’m interested in the traits that underlie this robustness and what this may teach us about amphibian developmental physiology in general and those species that might not be as robust as the chorus frog.

What inspired you to examine the effects of temperature fluctuations on Baja California Chorus Frogs?

When examining temperature, most physiologists, including myself, focus on constant temperatures, which is a perfectly reasonable place to begin exploring thermal physiology. However, that just is not truly representative of the natural environment. Furthermore, many predictions about how climate change will shape the thermal environment indicate that it is not just an increase in mean temperature but greater fluctuations in temperature that might impact species. We have a population of chorus frogs in a wetland located on the CSUSM campus, so it is easy to monitor temperature in a breeding habitat. After tracking temperature over a couple breeding seasons I was able to use the data to replicate the natural daily fluctuations in a lab setting. Using the field data I am able to examine embryonic and tadpole physiology under the current conditions and also look at temperature fluctuation regimes that might represent conditions under future climate change scenarios.  

How might climate change impact these frogs?

Even in this thermally robust species, any changes in the thermal environment are going to alter the phenotype. Most evidence we have suggests the species is adaptable, but we still need to do a lot more research. The research performed and published by my lab so far indicates that temperature does alter developmental phenotypes of the chorus frog, but we still need to understand the long-term impacts of this. For example, warmer temperatures, even during daily transient fluctuations, increases development rate and thermal tolerance. However, this influences energy use and often results in smaller individuals. To truly know the impacts of climate change we need to examine the phenotype of the chorus frog following metamorphosis to understand how increased temperature during development shapes performance later in life. 

What are you researching right now?

My lab is focused on three main thermal physiology research projects. In addition to the chorus frog work, we are examining metabolic responses in marine copepods in response to rapid temperature changes and the long-term effects of embryonic temperature on juvenile rainbow trout. Spring is when the lab is focused on chorus frogs and rainbow trout, so those projects were disrupted this year as the lab shut down due to Covid-19. The chorus frog research my undergraduate student, Marie Ramirez, planned to present at the 2020 Experimental Biology conference was showing our initial results for how tadpole function was influenced by different fluctuating temperature treatments. This year we were expanding this work by rearing embryos and tadpoles in fluctuating temperatures and then measuring function across a range of acute temperatures. This allows us to understand how fluctuations alter performance curves. We also planned to begin rearing tadpoles beyond metamorphosis so we could start exploring physiology at the next life stage. Hopefully, we’ll be able to continue this work next spring!

Categories: Climate Change, Nature's Solutions, Physiology on the Road

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