A University of Georgia A study recently determined that there are no fundamental differences between monarch butterflies that live in eastern North America and their western counterparts.
The advice emerged from a staged study to determine if the lighter color of the western butterfly caterpillar was due to greater exposure to sunlight.
Distance doesn’t matter
The two populations of butterflies — separated by the Rocky Mountains — are basically the same butterfly, according to UGA ecology researcher Andy Davis.
A study 17 years ago in Davis’s lab indicated that monarch caterpillars in California appear lighter in color than those that populate the east. This was thought to have happened due to the caterpillars’ greater sun exposure in the west.
That study, Davis said, was done with lab-bred caterpillars, but this new study was done using photos of caterpillars taken in the wild and available on websites.
The new research, according to Davis, shows that western and eastern butterflies are basically the same.
The study was published in the latest issue of the Journal of Thermal Biology, a scientific publication that publishes articles on the influence of temperature on humans and animals.
“A Long Talk”
Entomologists have long debated whether the western monarch is a different population than the eastern one, according to Davis.
“This is a long-standing discussion that people have had in the butterfly world,” Davis said.
“For a very long time people thought they were completely separated,” he said. Eastern monarchs migrate to Mexico for the winter, while western monarchs migrate to locations in California.
The monarch caterpillar has a distinctive appearance and is generally known to ordinary people. The body is striped with yellow, white and black bands.
Seventeen years ago, study in Davis’ lab at UGA found that monarch caterpillars in California appeared to be lighter in color than those in the east.
This recent study was conducted by Davis, Nate Nibbelink, a research professor at the Warnell School of Forestry, and Christian J. Deneka, an undergraduate ecology student.
The new study, according to Davis, was based on photographs taken of monarch caterpillars in the wild.
Sharing photos in the service of science
“Now, with the rise of the internet and online photo-sharing platforms, like iNaturalist, there are hundreds of thousands of butterfly caterpillar photos out there,” he said.
The study was a Deneka student project.
“I said to him, ‘Here are all these photos. Look at the study we did 17 years ago and try to replicate the results using these iNaturalist photos,” Davis said.
“Christian uploaded 500 images, some measurements of those images, and we were surprised to find that all of the images he looked at from the western part of the country were basically identical to those from the east,” Davis said.
Other studies have shown that western and eastern monarchs are genetically the same, Davis said.
“Now we think there’s no real western monarch. It’s really just an offshoot of the eastern monarch,” he said. The two populations migrate to different places in the winter, but Davis stated that they are in fact “a giant North American population”.
Davis described Deneka as a talented student.
“This particular project caught my eye because monarchs are a highly studied species and I was excited to be able to contribute to this body of work,” said Deneka, a Canton, Georgia native and graduate of Etowah High School.
Davis said Professor Nibbelink added important skills to the study.
“He did something cool with the study. He was able to figure out how to generate data on the temperatures of the places the photo was taken knowing the latitude and longitude and the date of the photo,” Davis said.
Nebbelink was able to determine the temperature that day from the photo. The study showed that in places where the temperature was lower, the monarch had more visible black bands on the skin, Davis said.
“This allows the monarch to occupy a huge range in North America. There are monarchs in almost every state in the country and in most provinces in Canada. There is no other butterfly that can make the same claim,” the scientist said.