Research Beat: Studying cicadas with Christine Simon

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As the pandemic begins to wind down this spring, Connecticut will have a whole new type of bug to contend with: the 2021 brood of periodical cicadas, also known as Brood X. Christine Simon is a professor of ecology and evolutionary biology at the University of Connecticut who has dedicated the better part of her career to studying cicadas.  

Simon said she studies cicadas because she was interested in studying how species formed, which is called speciation. Simon thought the best way to study speciation would be to look at species that were already closely related to each other. 

““That’s why I picked thirteen and seventeen-year periodical cicadas, because they had these different year classes called broods,” Simon said. “They’re essentially the same species, but because the adults come out in different years they’re reproductively isolated. In order to get speciation, you must first get reproductive isolation.” 

Simon explained studying the speciation of cicadas is just one part of the larger picture of evolution. 

“The main reason I was doing that was to build evolutionary trees that were accurate, so that I could reconstruct the evolutionary history of different species I was working with, so I could understand evolutionary questions,” Simon said. “So to understand how different characteristics of organisms evolve, how species originate, how they spread across a landscape and then how they spread around the world.” 

One way Simon studied this evolutionary history was to look at the symbionts of cicadas, which are other organisms which have a close, long-term relationship with cicadas. In particular, Simon studied bacteria which live symbiotically with the cicadas.  

“Cicadas feed on the watery fluid in tree sap, from the xylem of the plant. It’s a nutrient poor food source, so they rely on having specialized bacteria that make their essential amino acids,” Simon said.  

Simon looked at 50 different species of cicada in New Zealand to study this. By examining the bacteria in the cicadas, Simon and her team hoped to learn whether the bacteria allowed the cicadas to colonize new areas, or if colonizing new areas allowed the cicadas to develop the bacteria. 

There is much to be learned about cicadas. Photo courtesy of JanetAndPhil via Flickr

 As it turns out, this research had some surprising results.   

“We found out that sometimes the bacteria are replaced by fungi. These fungi take over the role of one of the bacterial symbionts, and the really cool thing is that fungi are typically parasites of cicadas. Usually, the fungi kill the cicadas,” Simon said.  

Somewhere along the line, Simon explained, these two organisms which were supposed to kill each other evolved, and the fungi became vital to the cicada’s survival. 

“Either the cicada has tamed the parasite and prevented it from killing it, or else the parasite has somehow evolved to live in the cicada and gain some sort of selective advantage from that,” Simon said.  

This evolution wasn’t just isolated to New Zealand either.  

“The fungus has evolved more than 17 times around the world to replace the bacterial endosymbiont,” Simon said.  

This isn’t all of Simon’s research. Simon also looks at how cicadas are affected by climate change. And, a lot of Simon’s day is taken up by doing outreach on behalf of the bugs.  

“Some people have a real phobia. Then there’s other people who just think bugs are icky. But then, there’s a lot of people who love them, especially kids,” Simon said.  

Part of this involves an app called Cicada Safari, which allows regular people to contribute to research around cicadas. Developed with help from Professor Gene Kritsky at Mount Saint Joseph University and Professor John Cooley from UConn, this app allows people to map the cicadas they see from Brood X. This data is then compiled into a map, which can be found at cicadas.uconn.edu.  

For Simon, this research is just an extension of a childhood passion for nature. 

“I was always interested in the natural world: insects, plants, beaches, rocks, shells. I used to collect everything when I was a kid,” Simon said.  

Now, she encourages other families to look at the natural world with their kids. 

“As soon as the sun goes down, the cicadas start coming out. You can watch them crawl up the trees and come out of their shells. You can watch them fly around, behave, mate, lay eggs,” Simon said. “It’s a good thing for families to do together. It’s really exciting.” 

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