Timing and continuity of heat waves affects sexual development in a turtle

Featured Scientist: Anthony Breitenbach (he/him/his), PhD in Biology (Anticipated: Spring 2021), School of Biological Sciences, Illinois State University

Anthony Breitenbach stands at the front of a room full of children and their parents. He holds a turtle in his hands and the children are watching intently.
Anthony Breitenbach, the “turtle guy”, teaches kids about turtles at Sugar Grove Nature Center in McLean County, IL

Birthplace: Connersville, Indiana

My Research: I’m interested in how hot temperatures affect whether individuals develop as a boy or a girl. This is important because heat waves are predicted to intensify in the future as a result of climate change.

Research Goals: We know a lot about sexual development in humans, but we don’t understand how it is affected by temperature for some organisms like turtles. I wish to continue researching how sexual development happens in nature.

Career Goals: I love to teach. I would love to continue teaching science to multiple different age groups.

Hobbies: I love reading nonfiction history books, playing video games, and listening to rock music!

Favorite Thing About Science: My favorite thing about science is its great purpose: to understand the world around us in a collaborative effort with many different people from many different backgrounds. Playing with fire gets you burned, but playing with science gets you learned!

My Team: I am the first author on this paper, but like all research, this was a cooperative effort. Multiple graduate and undergraduate students participated in the fieldwork by trapping turtles and collecting eggs. Graduate students also helped care for the eggs and the hatchlings. The principal investigator handled the controlled substances necessary for my research.

Organism of Study: Red-eared slider turtle (Trachemys scripta)

A turtle sits in the sand between a set of plants, preparing to lay her eggs.
Nesting T. scripta

Field of Study: Physiological Ecology

What is Physiological Ecology? People in the field of physiological ecology want to know how factors in the environment (like temperature) affect how the body develops.

Check out my original paper: “Using naturalistic incubation temperatures to demonstrate how variation in the timing and continuity of heat wave exposure influences phenotype”

A QR code that links to the original publication.
QR Code to the original publication

Citation: Breitenbach AT, Carter AW, Paitz RT and Bowden RM 2020. Using naturalistic incubation temperatures to demonstrate how variation in the timing and continuity of heat wave exposure influences phenotype. Proceedings of the Royal Society B. 287: 20200992.

Research at a Glance: In animals that have temperature-dependent sex determination, whether the animal is a boy or a girl depends on the temperature while they are in their eggs. In a lot of turtles, warm temperatures cause the turtles to become girls while cool temperatures cause the turtles to become boys. The research that we know this from has been in labs with constant temperatures that never change while the animals are in their eggs. This is different than natural temperatures. We know that temperatures change, usually by increasing during the day and decreasing during the night. My research looks at how temperature affects whether turtles become boys or girls when the temperature is fluctuating, or going up and down in a repeating cycle. My research found that warm temperatures are most likely to cause turtles to become girls if the warm temperatures happen during the middle of development. It also found that more turtles become girls if warm temperatures are continuous, rather than spread out over a longer period of time. Lastly, my research found that two genes respond differently to continuous warm temperatures compared to warm temperatures spread out over a longer period of time. Since heat waves will likely intensify as a result of climate change, the results suggest that more turtles will be girls and less turtles will be boys in the future, which could cause problems for turtle species.  

Highlights: One experiment found that more continuous warm temperatures make it more likely that a turtle will be a girl. To come to this finding, I placed turtle eggs in incubators that let me control the temperature. Eggs were moved between a cooler condition of 25 ± 3 °C and a warmer (heat wave) condition of 29.5 ± 3 °C. Some eggs were exposed to a continuous 12-day heat wave and others were exposed to 12 heat wave days spread out over a longer period of time. A 12-day heat wave made it much more likely for turtles to become girls. It was much less likely for the turtles to become girls when they experienced discontinuous warm temperatures (Figure 1).

A bar graph that shows the probability that a heat wave of 12 or 6 days applied early or late in development will result in a female turtle. The figure shows that a 12-day heat wave applied early in development has the highest probability of creating a female. The bar for a 12-day heatwave is between 0.5 and 0.75 on a 1.0 scale, all others are 0.25 or below.
Figure 1. The horizontal axis shows the different heat wave treatments. The vertical axis shows the probability that a turtle will end up being a girl as a result of the heat wave treatments.

The results show that it is much more likely for turtles to become girls when they experience an early 12-day heat wave when they are in their eggs. If that 12-day heat wave is delayed until later when they are in their eggs, it becomes less likely for turtles to become girls. If a total number of 12 heat wave days is split up into either two 6-day heat waves or four 3-day heat waves, the probability that turtles will become girls drops even more.

What My Science Looks Like:

An infographic that describes how Anthony Breitenbach does his research. Panel 1 titled "Step 1: Get Turtle Eggs", shows turtle eggs in the ground. Panel 2 titled "Step 2: Expose Them to Variable Temperatures", shows an incubator. Panel 3 titled "Wait Until They Hatch", shows a clock. Panel 4 titled "See How Many Are Girls And How Many Are Boys", shows the word "Results!".
Pictured here is a brief layout of the steps of my research

My research focuses on controlling the temperatures that turtles experience while they are in their eggs. This is interesting because the temperature in the environment influences whether the turtles become girls or boys. Most of what we know about how this system comes from research done in laboratories using constant temperatures. My research involves exposing turtle eggs to more variable temperatures, such as heat waves. After the eggs hatch, I then check to see how many became girls and how became boys. These results can shed light on how the environment can have long-lasting effects on animals!

The Big Picture: As a results of climate change, heat waves are likely to get hotter and longer. This could result in the production of many more girls compared to boys for animals like turtles and certain other animals. If this happens, then these animals will have a much more difficult time finding mates, which means that the numbers of these animals will go down. Since most research in this field has used constant temperatures, it’s important to further our understanding of how more variable temperatures affect these species.

Decoding the Language: 

Climate change: Climate change refers to changes in climate patterns (such as temperature, precipitation, etc.), particularly as a result of the increased emissions of carbon dioxide and other greenhouses gases starting in the mid to late 20th century.

Ecology: Ecology is a field of science that studies organisms and their relationships with surrounding organisms as well as with their surrounding physical environment

Fluctuate: In the context of this article, fluctuate refers to the temperature that the eggs were exposed to. I used a temperature that would rise and fall repeatedly.

Gene: A gene is a  unit of heredity passed from parents to offspring. Genes normally code for proteins that have certain functions in the body.

Physiological Ecology: Physiological ecology is a field of science that studies the normal functions of the bodies of living organisms. We look at how the body of the organism responds to the environment. 

Principal Investigator (PI): In the context of academia, a PI is a university faculty member that supervises the research of the laboratory. The PI is generally responsible for running the lab, financing the research through grant applications, and training graduate and undergraduate students.

Probability: Probability refers to  the likelihood of something happening. In the context of this article, it refers to the likelihood that a turtle would hatch as a boy or as a girl. 

Temperature-dependent sex determination(TSD): TSD is a type of sex determination system where the environmental temperature that an individual is exposed to during embryonic development (in the egg) determines whether it will develop into a boy or a girl.

Learn More:

To learn more about reptiles/amphibians in general: Vitt, L. J., & Caldwell, J. P. (2014). Herpetology: An Introductory Biology of Amphibians and Reptiles (4th ed.). Amsterdam (Holanda): Elsevier.

You can use this book to learn more about turtles:Ernst, C. H., & Lovich, J. E. (2009). Turtles of the United States and Canada. Baltimore, MD: John Hopkins University Press.

You can use this book to learn more about TSD:Valenzuela, N., & Lance, V. (2004). Temperature-dependent Sex Determination in Vertebrates. Washington, D.C.: Smithsonian Books.

Synopsis edited by: Madison Rittinger (she/her/hers), M.S. (Anticipated Spring 2021) and Casey Gahrs (she/her/her), M.S. 2020, School of Biological Sciences, Illinois State University

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