Mudskippers could be key to understanding evolution of blinking

Blinking is crucial for the eye. It’s how animals clean their eyes, protect them, and even communicate. But how and why did blinking originate? Researchers at the Georgia Institute of Technology, Seton Hill University, and Pennsylvania State University studied the mudskipper, an amphibious fish that spends most of its day on land, to better understand why blinking is a fundamental behavior for life on land.

Although mudskippers are distantly related to tetrapods, the group that includes humans and other four-limbed vertebrates, researchers believed studying the fish could unlock how blinking evolved as these animals began to move on land. 

The research team, which included several undergraduates, published their findings in the paper, “The Origin of Blinking in Both Mudskippers and Tetrapods Is Linked to Life on Land,” in Proceedings of the National Academies of Science.

“By comparing the anatomy and behavior of mudskippers to the fossil record of early tetrapods, we argue that blinking emerged in both groups as an adaptation to life on land,” said Tom Stewart, an assistant professor at Penn State and an author of the paper. “These results help us understand our own biology and raise a whole set of new questions about the variety of blinking behaviors we see in living species.”

Breaking Down Blinking

Mudskippers blink by sucking their eye downward into their eye socket. The evolution of this behavior did not require the evolution of a lot of new parts such as new muscles or special glands, though. Instead, mudskippers use their existing set of eye muscles in a new way.

“This is a very exciting result because it demonstrates that the evolution of a new, complex behavior can be achieved using a relatively rudimentary set of structures,” said Brett Aiello, a former postdoctoral fellow in the Agile Systems Lab and now assistant professor at Seton Hill.

Next, the research team set out to determine why mudskippers blink. In a series of experiments, they found that mudskippers blink for three main functions: to wet, clean, and protect the eye. These functions are also why humans and other land-dwelling vertebrates blink.

“We find that a single behavior can be deployed to accomplish three complex, distinct functions,” said Aiello. “These results not only help humans understand our own history, but also help us reevaluate the adaptations necessary for major transitions in the evolutionary history of vertebrates, like moving from water to land.”

Blinking isn’t just a unique research question, but also an important mechanism to understand, according to Saad Bhamla, an assistant professor in Georgia Tech’s School of Chemical and Biomolecular Engineering and author on the paper.

“We all blink without thinking, and understanding why we blink is just such a beautiful puzzle right in front of our eyes,” Bhamla said. “Through our research on mudskippers and by conducting biophysical and morphological analyses, we expose how blinking serves a multitude of functions for adapting to life out of water.”

Engaging Undergraduates

To explore such open-ended questions, the researchers engaged the Vertically Integrated Projects (VIP) program, which allows undergraduates to conduct long-term, large-scale research projects as part of their coursework at Georgia Tech.

“The structure of the VIP course empowers students to really lean on their own creativity and drive the project in the directions that are most exciting to them,” said Aiello. “It helps our students gain the ability to solve unknown problems on the ground as they arise — a lot of people become scientists to push research somewhere where nobody else has tried to go before.”

The VIP structure is inherently multidisciplinary. While Aiello is a biologist, most students were engineers and brought their respective expertise. Manognya Sripathi was a biomedical engineering major with a minor in computer science and offered her unique experience to the mudskipper problem.

“I used my computer science skills to gather raw data and analyze and plot them using programs like MATLAB or Python,” Sripathi said. “I also used engineering skills to help build the experimental equipment, allowing us to apply engineering methods to study a biological problem in a unique way.”

Moving Beyond Mudskippers

Te research didn’t just expand knowledge of mudskippers — it also contributed to each student’s future aspirations. For example, Kendra Washington’s trajectory was influenced by the two semesters she spent in the lab.

“VIP drew me closer to the programming and device areas of my biomedical engineering major and solidified why I picked up a computer science minor,” she said. “I continued to pursue that fusion through later internships and research, and now work with hemodynamic monitoring. But in a sense, I still help characterize physiology through programming.”

VIP also expanded the students’ knowledge and scientific experience that have propelled them far beyond the lab. Hajime Minoguchi, a biomedical engineering graduate, now works as a systems integration research and development engineer thanks to his experience in the class.

“Working in an interdisciplinary team like this has allowed me to learn how to understand and communicate ideas between disciplines, which allowed me to be a more well-rounded engineer,” Minoguchi said. “My work requires a thorough understanding of biology, electrical circuitry, software, firmware, mechanical interactions, and physics. This VIP experience was instrumental for me in being successful at my current job.”

The research is far greater than the sum of its parts and brings a greater understanding of evolution, noted Simon Sponberg, an associate professor in the School of Physics and the School of Biological Sciences.

“Blinking is a reflection of a bigger question,” Sponberg said. “How did major evolutionary transitions occur that enabled organisms to inhabit basically every environment on this planet? What we learned is you don't need the evolution of a lot of specialized musculature or glands; evolution can tinker with the structures that are already there, allowing them to be used in a new way and for a new behavior.”

CITATION: Aiello BR, MS Bhamla, J Gau, JGL Morris, K Bomar, S da Cunha, H Fu, J Laws, H Minoguchi, M Sripathi, K Washington,G Wong, NH Shubin†, S Sponberg†, TA Stewart. The origin of blinking in mudskippers and tetrapods is linked to life on land.  Proceedings of the National Academy of Sciences

DOI: 10.1073/pnas.2220404120

######

The Georgia Institute of Technology, or Georgia Tech, is one of the top public research universities in the U.S., developing leaders who advance technology and improve the human condition. The Institute offers business, computing, design, engineering, liberal arts, and sciences degrees. Its more than 45,000 undergraduate and graduate students, representing 50 states and more than 148 countries, study at the main campus in Atlanta, at campuses in France and China, and through distance and online learning. As a leading technological university, Georgia Tech is an engine of economic development for Georgia, the Southeast, and the nation, conducting more than $1 billion in research annually for government, industry, and society.