Visual system of butterflies changes with seasons
An analysis of Buckeye butterflies finds that they aren’t just changing colors with the seasons but changing the way they see on a physiological level
image:
Left two images are of darker, fall butterflies. Far right is lighter summer coloring.
view moreCredit: Grace Hirzel and Erica Westerman
The shift from warm summer to cool fall conditions can be stressful for many animals. Surviving each season requires a multitude of different physiological and behavioral traits that scientists are still working to understand.
One of the more obvious ways that animals respond to seasonal conditions is by changing their coloration to better suit the time of year. The common buckeye butterfly (Junonia coenia) has been of scientific interest for over a hundred years because of the stark contrast between summer adults that emerge with light wings and fall adults that emerge with dark wings. One explanation for the darker coloration is that it helps increase body temperature in cooler weather, as does the increase in time spent basking to soak up sunshine.
A team of researchers led by the University of Arkansas, in collaboration with Cornell University, wanted to see if they could connect these two seasonal changes with genetic changes underlying the butterflies’ visual systems. Ulitmately, they hoped to confirm that seasonal change in wing color is also accompanied by changes in behavior and sensitivities to certain colors, since color vision informs many butterfly behaviors.
The team caught and recorded the behavior of common buckeyes in northwest Arkansas prairies (specifically Woolsey, Chesney and Stump prairies) from May to November between 2018 and 2021. From eye tissue obtained from captured butterflies, they examined how patterns of gene expression differed between dark fall butterflies and light summer butterflies. They found that compared to light summer butterflies, darker fall butterflies are more likely to spend their time basking.
Though they didn’t find evidence that the common buckeye’s sensitivity to color differs with time of year, the team did confirm seasonal patterns in the expression of many other genes important for vision and eye development. This indicates common buckeyes may see their environment differently, depending on what time of year they develop as caterpillars.
The next step will be to determine what part of the developmental environment is causing these changes in the visual system (butterflies only live 8-10 days as adults, so they only experience one season). Is it a change in temperature, a change in their visual environment or some other sensory cue?
Observational studies investigating behavior and underlying gene expression in wild populations of animals are uncommon, since natural settings can introduce variance that makes it hard to discern significant patterns. This study reports strong patterns of seasonal response, even outside the controlled conditions of a lab.
Grace Hirzel was first author on the paper published in Functional Ecology. She conducted most of the field work as a Ph.D. student in biological sciences at the U of A while working with Erica Westerman, an associate professor of biological sciences who is the corresponding author on the paper.
“Working with wild populations allowed us to examine how animals are responding to time of year as whole and under natural settings,” Hirzel explained. “Not only are common buckeye butterflies interacting with their world differently depending on the time of year, but they probably see the world differently at these times of year too. Buckeye butterflies are just one of the many species with obvious seasonal traits. Changes in sensory system development like we found in the buckeye may be a common strategy used by many animals to survive shifting seasonal conditions.”
Westerman specializes in studying the visual systems of butterflies. Why butterflies? She says she’s interested in the big picture question: do our sensory systems change with our environment and how plastic is our sensory system?
“A great place to start is with a species that you know exhibits plasticity in other areas,” Westerman said. “So, we knew they had plasticity in their wing pattern. If we’re going to get plasticity out in nature in a sensory system, buckeye butterflies are a good species to use...So this is us getting our foot in the door and really trying to answer that big question of ‘how does the development environment influence our sensory perception?’”
Westerman also noted that “one of the reasons we work with this butterfly is that while it’s found throughout the country, it's in really high abundance here in Arkansas. It’s been used for developmental research and understanding how butterflies work for decades. But those populations have always been from the coast where it’s just not quite as common. It meant a lot to me and Grace to work with a local population here. It's a common Arkansas butterfly and it’s really pretty, and I think it's important that some of the species that are common here in Arkansas and the central plains also get showcased in the greater scientific community.”
Co-authors on the paper from the U of A also included Keity J. Farfán-Pira, a postdoctoral fellow in biological sciences, and Chance Powell, a Ph.D. candidate in the same department. Contributors from Cornell included Noah K. Brady, a Ph.D. candidate at the time, and Robert D. Reed, a professor of ecology and evolutionary biology.
Journal
Functional Ecology
Method of Research
Observational study
Subject of Research
Animals
Article Title
Synchronous seasonal plasticity in coloration, behaviour and visual gene expression in a wild butterfly population
