Trio of MC alums digs into turtle DNA, settles decades-old controversy

May 1, 2014

Placed side-by-side, Graptemys nigrinoda turtles seem to have two distinct subspecies.

But a recent inquiry into their DNA by three Maryville College graduates has revealed that, despite often dramatic differences in appearance, the turtles are all one and the same. Those findings will be published in the journal of the United Kingdom-based Linnean Society, which is the world’s oldest extant biology society.

Graptemys nigrinoda live in rivers throughout Mississippi, Alabama and Georgia. Their shape, size and color change depending on where they live.

For instance, turtles living near the Mobile Bay Basin, where the rivers drain into the Gulf of Mexico, have a darker color and higher domed shells. That’s because they live in murky and slow-moving water.

But the researchers concluded those variations are localized, geographic adaptations rather than indications of separate subspecies.

Adam Patterson ’13 said: “At first glance, if you were to compare the two, you’d think they were two different types of turtles. But when you take a look at the genetics there just wasn’t enough genetic variation to classify them as separate subspecies.”

Marly Kalis ’13, whose senior thesis the publication is based on, said she compared more than 60 physical characteristics of the turtles.

Her advisor, Dr. Josh Ennen ’03, is a scientist at the Tennessee Aquarium Conservation Institute. He was a visiting professor at the time of the research and contributed his expertise in DNA and morphometric analyses.

Hundreds of turtles had to be measured, and the specimens came from places as varied as the Auburn University Museum of Natural History, the Carnegie Museum of Natural History in Pittsburgh, and the University of Alabama Museum of Natural History.

Patterson is now the lead animal trainer of the Knoxville Zoo and said producing research for publication was one highlight of his Maryville College education.

“Taking measurements the way we did - we went through hundreds of turtles - taught me patience for detailed work, which will definitely stick with me,” he said. “Just knowing that I was able to get my name in a biological journal is very exciting. That feeling of accomplishment and fulfillment is a fantastic feeling.”

Kalis, who is pursuing a career in natural and alternative medicine, said Graptemys nigrinoda have been a source of controversy since the early 1970’s. She had been fascinated for some time and “already had collected half the data going into [her] senior year.

“The tools and research needed to complete this project and the experience of what it takes to be a part of a publication - as well as becoming confident and knowledgeable enough to speak in front of my professors and peers - will help me tremendously in my present and future endeavors,” she said. “I loved working on this project.”

The fact that the Maryville College trio settled this decades-old controversy using genetic testing carries wide-reaching implications, Kalis said. A large part of biology involves “systems of separation and naming of animals.”

“This study focuses on how we should separate organisms. Should scientists focus on genetic differences or physical differences?” she asked. “With the advancement of technology, how well will our old naming systems hold up? We have been separating organisms based on their physical traits. That’s why this study is so significant to biology today.”

Ennen, whose accomplishments include the discovery of a new turtle species in 2010, praised the work of both Patterson and Kalis as exemplary.

“Marley and Adam collected all the data, and Marley was instrumental in writing the manuscript,” he said. “Very few undergraduates at any university or college have the opportunity to conduct - let alone publish - quality research.”

By Gerhard Schneibel, News and New Media Writer


Maryville College is ideally situated in Maryville, Tenn., between the Great Smoky Mountains National Park and Knoxville, the state's third largest city. Founded in 1819, it is the 12th oldest institution of higher learning in the South and maintains an affiliation with the Presbyterian Church (USA). Known for offering its students a rigorous and highly personal experience that includes an undergraduate research requirement, Maryville College is a nationally ranked institution of higher learning that successfully joins the liberal arts and professional preparation. Total enrollment for the fall 2013 semester is 1,168.