Biology Ph.D. student lauded for work on salamander reproduction

Biology Ph.D. student lauded for work on salamander reproduction

As she nears the finish line of her doctoral studies in biological science, Madison Herrboldt has a spring in her step after learning that a publication on which she was the lead author was recently selected as the winner of the 2021 Zuckerkandl Prize. Herrboldt’s peer-reviewed paper – “Pheromone gene diversification and the evolution of courtship glands in plethodontid salamanders” – appeared in the Journal of Molecular Evolution last August.

woman with long blonde hair smiling and standing outdoors
Madison Herrboldt

“Receiving this honor made me feel proud, humble and fulfilled,” said Herrboldt. “It is all a bit surreal to have the first publication I’ve ever written myself – with the help of my advisor, Professor of Biological Science Ron Bonett – be recognized in this way. I want to underscore that I could not have accomplished this without the expertise and contributions of my co-authors. They deserve huge congratulations too.”

For Herrboldt, receipt of the Zuckerkandl Prize is helping her believe that her research is meaningful to a broader scientific community. “As an emerging scientist,” she reflected, “you can easily doubt yourself, your capabilities and whether your research is of interest. But this award has really boosted my confidence as both a scholar and a writer.”

Prior to Herrboldt’s arrival at TU, Bonett and his students had conducted some preliminary investigations of salamander pheromones. “But Madison really added an extra dimension to the project,” Bonett explained. “She was dedicated to doing what was needed to complete the project and get it into a prominent journal. The Zuckerkandl Prize was well deserved, and I anticipate that Madison will continue on to an excellent career in reproductive biology.” In addition to lauding her as a first-rate researcher, Bonett pointed out that Herrboldt has proven to be an inspiring research mentor for the department’s undergraduate students.

Biology 101

Even as a child growing up outside St. Louis, Missouri, Herrboldt had a strong passion for animals and a desire to understand how and why they behave and adapt. “My favorite class in high school was biology,” she recalled. “Early on, I developed an interest in the methods that can be utilized for species conservation.”

While completing a Bachelor of Science degree at Southeast Missouri State University, Herrboldt focused her attention on animal reproduction. To that end, she studied oviducts and sexually dimorphic glands in salamanders.

“If you had told me during my freshman year that I would one day be getting my Ph.D. and my specialty would be salamander reproduction, I would’ve thought you were nuts,” Herrboldt laughed. “But when I started doing research in Professor Dustin Siegel’s lab, I really fell in love with salamanders – both as fascinating organisms and as a model system.”

Up close with the salamanders of Oklahoma

Herrboldt’s undergraduate work revealed to her salamanders’ unique developmental phenomena and complex life cycles, two factors that make them ideal for the study of evolutionary biology. Indeed, there is a direct through-line to Herrboldt’s current research at TU.

The focus of Herrboldt’s dissertation and prize-winning paper is salamander pheromone gene duplications and how those genes have evolved gland-specific expression. There are many evolutionary models for what may happen to a gene after it duplicates, and one is to take on a new function, explained Herrboldt. Her paper offers an example involving genes that are utilized to signal reproductive status to prospective mates and how developmental shifts may impact communication through these chemical signals.

Professor Bonett has had an incredible influence on me. Not only have I learned new lab techniques, data analysis methods and how to be a better writer during my time in his lab, but his guidance has made me a more confident scientist.

My passions and goals are fully supported in this lab, both by Professor Bonett and my lab mates. They challenge me, they teach me, they support me, they help me see things from a different perspective, they build me up when I am down. Without them, I would not be who I am today.

I am also thankful to Professor Alexandra Kingston. She has taught me new techniques, proofread my papers and has done so much else to help me succeed. As a young female scientist, I really look up to her.

One of the most interesting findings reported in Herrboldt’s prize-winning paper is that differences in salamander development have led to the loss of an entire courtship gland and the associated pheromone genes in the Oklahoma salamander (Eurycea tynerensis). Male salamanders in the Eurycea genus have two courtship glands that secrete pheromones: the mental gland, located on the chin, and the caudal gland, located at the base of the tail. Herrboldt and her colleagues examined the pheromones produced by both.

The team’s research identified the expression of eight gene copies of the salamander pheromone Sodefrin Precursor-like Factor. Investigation found that these copies of the signal are gland specific across all the taxa they studied: Some are produced only in the mental gland and some only in the caudal.

Among Oklahoma salamanders, one finds metamorphic and paedomorphic examples. Not unlike frogs, the former lay eggs in water, the eggs develop into larvae/tadpoles and then the larvae metamorphose into land-dwelling adults. The latter, meanwhile, do not go through metamorphosis; instead, they become aquatic reproductive adults that retain certain larval characteristics.

By studying the pheromone profiles in these two life cycle models, Herrboldt found that paedomorphic Oklahoma salamanders lack a mental gland and do not produce the pheromones associated with the mental gland. This stands in contrast to the metamorphs of the same species.

Further investigations warranted

Armed with this new knowledge, which forms the basis of chapter two of her dissertation, Herrboldt is now testing how life-cycle shifts, such as one sees in the Oklahoma salamander, impacts salamander pheromone evolution. “There are instances in the family of salamanders (Plethodontidae) I study in which paedomorphosis has evolved multiple times,” Herrboldt noted. “It will be interesting to see whether all paedomorphs lack a mental gland and the associated mental gland pheromone genes.”

Herrboldt is also keen to someday explore the implications of her work on reproductive isolation and speciation. A question she and her colleagues hope to answer is whether paedomorphic Oklahoma salamanders, which their research has shown have lost a major courtship gland and the associated pheromones, are able to breed with their metamorphic counterparts.

Beyond that inquiry, after she completes her doctorate this summer Herrboldt is hoping to continue her research on the salamander pheromone system while holding a postdoctoral fellowship and, eventually, a professorial position. “There is so much more to learn about this topic, including the mechanisms involved in how male pheromones lead to behavioral outcomes among females,” Herrboldt said.

In addition, she wants to expand her methods repertoire. “Right now,” Herrboldt explained, “neuroscience techniques are not widespread in the study of salamander pheromone communication. I would really like to learn these methods and apply them to my system.”

Does deep scientific exploration of the natural world fascinate you? If so, consider digging into graduate studies in biological science – a diverse field rich with scholarly adventure and career satisfaction.