Noah Leith: Understanding how thermoregulation affects insect survival and reproduction in the face of climate change 

Noah Leith: Understanding how thermoregulation affects insect survival and reproduction in the face of climate change 

In this ‘Behind the Paper’ blog post, Noah Leith – a PhD candidate in the Fowler-Finn Lab at Saint Louis University – discusses his research article Thermoregulation enhances survival but not reproduction in a plant-feeding insect, which was recently published in Functional Ecology. Noah discusses the impacts of thermoregulation on treehopper survival and reproduction, the joys of temperature models, and how his interest in animal communication and experiences of queer ecology have influenced his work.

Click this link to listen to the treehoppers’ vibrational songs recorded by Noah and team in this research!

About the paper 

Rising temperatures and extreme weather events increasingly threaten animal populations around the world. A central goal for modern ecologists is therefore to understand the mechanisms by which animals could persist in rapidly changing climates. One such mechanism is behavioral thermoregulation. Thermoregulation allows animals to avoid stressful temperatures and/or seek out the best temperatures in their habitats, and research to date suggests that thermoregulation could allow many animals to survive in altered climates. Yet, survival alone is insufficient for population persistence—animals must also successfully reproduce to persist in our warming world. Even if thermoregulation ensures survival, populations could still be vulnerable to climate change if they cannot maintain the narrower temperature ranges required for reproduction. 

We sought to understand the relative benefits of thermoregulation for survival and reproduction in treehoppers—small insects that spend their entire lives on plants. Like many insects, treehoppers coordinate mating using male-female courtship duets that transmit as vibrational songs through plant tissues. However, treehopper mating activity is limited to a narrow window of temperatures, and exposure to hot microclimates could induce lethal heat stress. We used thermal imaging to measure available microclimates and the body temperatures of living treehoppers in netted plant mesocosms. This allowed us to estimate the potential survival and reproductive benefits of thermoregulation under different environmental conditions. 

A group of female Enchenopa binotata treehoppers on their host plant, Ptelea trifoliata wafer ash (Credit: Noah Leith) 

Netted mesocosms used in this study (Credit: Noah Leith) 

Microclimates were extremely variable on the treehopper’s host plants. Although treehoppers were often exposed to potentially lethal temperatures, they almost always ensured survival by rapidly leaping to other plant surfaces at the onset of overheating. By contrast, they did not actively seek out suitable mating temperatures, selecting temperatures at random in the absence of heat stress. In fact, suitable mating temperatures were often completely unavailable, especially at warmer air temperatures. Our paper reveals that overlooking the thermal sensitivity of reproduction may lead researchers to overestimate thermoregulation’s ability to buffer populations from climate change.  

About the research  

Our study emphasizes how important it is to understand the unique behavioral mechanisms by which animals navigate temperatures in their habitats. Like many insects, treehoppers simply jump off their host plants at the onset of heat stress and hope to land in a less stressful microclimate. While it may seem inefficient, this strategy could be more cost-effective than spending a lot of time and energy trying to navigate the extremely variable temperatures in their habitats. Observing how treehoppers avoid the worst habitats rather than seeking out the best allowed us to understand why our results better conformed to some theoretical models of thermoregulation over others. I think incorporating these different behavioral strategies of thermoregulation into theory will be key to predicting how thermoregulation affects vulnerability to climate change. 

Treehoppers and 3D-printed operative environmental temperature models. Each model is 5mm in length (Credit: Noah Leith)

One aspect of this project that I found really fun was creating the “operative temperature models”, which are tools that thermal ecologists use to estimate the body temperatures of non-thermoregulating animals. Designing and constructing operative temperature models presented a perfect opportunity to meld my interests in science and visual arts. To accurately estimate body temperatures, these models need to intricately mimic an animal’s color, shape, and other characteristics that dictate heat transfer between the animal and its environment. However, creating hundreds of models that realistically mimic insects presents a unique challenge—insects, particularly treehoppers, are super tiny (about 5mm in length). We used 3D-printing to consistently construct realistic models of treehoppers, which to my knowledge represent the smallest synthetic operative temperature models ever constructed. 

About the author 

I have always been captivated by the diverse and beautiful ways that animals communicate. I’m sure I wasn’t the only kid that desperately wanted to speak with their pets. So, I was completely enthralled when my eventual PhD advisor, Kasey Fowler-Finn, introduced me to treehoppers and the world of vibrational communication. So many animals communicate using vibrations—from nearly all singing insects like treehoppers, to rodents, reptiles, and even elephants. It blew my mind completely that this hidden vibrational world was hiding in plain sight. Exploring how temperature affects the expression, function, and evolution of vibrational signals and other forms of communication continues to be a major focus of my work. Since collecting the data for this study in 2019, my collaborators and I have also explored several ways that thermal physiology and reproductive traits interact to shape vulnerability to climate change. In the final stages of my PhD, I am also using wolf spiders to examine how North American temperature and precipitation gradients together affect the evolution of complex mating displays.  

Treehoppers coordinate mating using vibrational songs that travel through the stems of their host plants. Males and females coordinate their songs in repeated duets. (Credit: Noah Leith)
The author, Noah Leith (Credit: Noah Leith)

As a queer scientist, I feel naturally drawn to research that examines diversity in animal reproduction—including reproductive interactions that seem to disrupt societal norms of gender and human sexual behavior. But I’m especially drawn to work that uses a broader application of queer ideology to challenge perceived binaries in nature or generate new research questions. In this way, I think queer ecology closely aligns with what many researchers would consider an imperative of science in general: to gain insights about the natural world by challenging longstanding assumptions about how the world works. In global change biology, this could simply mean considering how organisms are threatened by environmental change in a diversity of contexts beyond the binary of life and death. 

Like the blog post? read the full paper here.

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