Cronin’s lifelong love of mantis shrimp

Senior scientist makes a life’s work investigating visual ecology

By Kennedy Lamb

Typing away on his computer, Thomas Cronin, a professor at the University of Maryland, Baltimore County,  writes an email to a colleague in Australia about new findings of peculiar color vision of mantis shrimp. He turns away for a moment, coffee cup in hand, leans back in his chair, and sits in pensive silence for a few moments.

“People often ask me what mantis shrimp see, and I reply they see what they’re looking at,” he said. “We don’t really know what they see, they see the world so differently from us.”

Cronin’s fascination with mantis shrimp began when he was an undergraduate at Dickinson College, but wasn’t pursued until he arrived at UMBC in 1983. He was always fascinated with sea creatures, having studied how light controls behavior in larval crabs at Dickinson, but didn’t believe that was the right time to divulge in studying mantis shrimp.  Back then, he said, the mantis shrimp were not as popular a model as they are now.

“No one knew what a mantis shrimp was, but now undergrads will come up to me saying, ‘Do you know about the color vision of those crazy shrimp?’ and I can say we discovered that right here!”

Mantis shrimp arguably have the most complex set of eyes in the entire animal kingdom. They have 12-16 different photoreceptors – light-detecting cells that allow the perception of color – but can’t decipher color as clearly as animals with fewer photoreceptors. The shrimp see color through a very small line (the midband) in their visual world, but they integrate that color sense with the spatial information they receive by rotating and swinging their eyes around to make sense of the world around them.

Cronin hypothesizes that the reason mantis shrimp have such a complex visual system is because their brains aren’t large enough to process the vast amount of visual data absorbed by their eyes. The structure of their eyes process most of the data, limiting the amount of information the small crustacean’s brain must process.

“Testing hypotheses like that are almost impossible,” Cronin says. “We don’t know how to get into their brains and analyze their visual centers.”

There is plenty of research that can be conducted on mantis shrimp. Cronin jokes that the shrimp are “happy to answer questions” for researchers, the only problem is that the answers are in a language that is difficult to understand.

Cronin wants to learn more about why the shrimp view light so differently from other animals (polarized light system) and how the eyes of mantis shrimp adapt different habitats. Mantis shrimp live in the deep sea, coral reefs, murky waters, among other saltwater locales.

“It’s an endless job,” he says. “The more you learn, the more you realize that you don’t know much at all.”

Cronin is nearly as famous as his beloved shrimp. His discoveries have made him one of the leading visual ecologists in the world. His work has been covered by the Los Angeles Times and National Geographic, and other national media.

In 2014, Cronin and three other visual ecologists authored an award-winning textbook called Visual Ecology that provided the first up-to-date compilation of findings of the field in more than thirty years. One Cronin’s co-authors, Sönke Johnsen, says that Cronin deserves his stellar reputation.

“He has the ability to look at the field from a much broader perspective because he has been in the field for such a long time.If he retires, there will be an enormous hole,” Johnsen said. “He holds this field together.”

Cronin attributes most of his success to luck.

“I was very fortunate to work with mantis shrimps because they have a tremendous amount of charisma. Their visual systems are unexpectedly wonderful and people really seems to like them,” he said. “It was really lucky to be working with such an interesting animal – it put me on the map.”

Cronin acknowledges that his drive and ambition may have contributed to his many achievements, but he modestly downplays his accomplishments.   

“When I first started I really wanted to be a success. But there are plenty of people who think that, and they aren’t in the top of their field,” he said. “I wasn’t predestined to do anything special, I just made a choice that worked out well.”

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