Turtles Go Royal

If you’ve spent any time during the summer near Washington College’s biology department, you can’t have missed Aaron Krochmal, associate professor of biology, and his team of undergraduate researchers. Usually wearing muddy boots and staring intently at a radio transmitter, they have been steadily uncovering the mysteries of how Eastern painted turtles learn how to navigate when they migrate.

Their work from last summer, along with Krochmal’s colleague Timothy C. Roth, assistant professor of psychology at Franklin & Marshall College, has revealed that turtles use spatial memory as they navigate over land. And, their new findings have earned them the cover story in one of the most prestigious international science journals, the Proceedings of the Royal Society B, Biological Sciences.

The cover photograph in the Feb. 10 issue—a baby Eastern painted turtle in mid-migration—was taken by Baker Gerwig ’14, a Washington College biology major who was among the students who have conducted research on the turtle project.

Krochmal has been studying the migration patterns of Eastern painted turtles every summer for seven years. Little is known about how turtles find new habitats or return to old ones until now, largely because scientists could never be sure when turtles would leave a pond and start traveling. Krochmal solved that problem when he started his research in 2009 on an Eastern Shore farm near the College, where every summer a large pond is drained on a set date, forcing the turtles to move. Krochmal, Roth, and their undergraduate researchers are able to monitor where turtles go and how they get there. Previously, the team has shown that turtles are capable of learning how to navigate until they are four years old, after which turtles appear incapable of learning proper migration routes.

Last summer, using pharmacological manipulation, they were able to determine that turtles use spatial memory as they navigate their overland habitat. Using scopolamine, a drug frequently used in humans to block memory, Krochmal and Roth manipulated the brains of migrating turtles—both young and old—as they navigated after leaving the pond.

“We knew from our previous work that turtles four years and older are unable to navigate the paths,” Krochmal says, referring to a critical period in which turtles must learn to navigate. “However, from hatching to three years old, they learn very well. We wanted to see what cognitive mechanisms the turtles used to do this. Based on previous research on spatial memory in turtles, we knew that acetylcholine was an important chemical for learning and memory. So, we thought that we could use it as a tool to manipulate turtle memory in the wild. It was very far-fetched. I thought, no way this will ever work. Tim, my colleague, and I argued fiercely about it. And then finally we said, fine, we’ll do it. And it worked spectacularly.”

Experienced turtles that typically navigated with extreme precision became lost when given the drug, but not when given a control. Inexperienced juveniles that have no memory and seem to navigate by sensory cues were unaffected and continued to follow complex routes unimpaired.

“These results suggest the importance of spatial memory in complex navigation and highlight cognitive and neural mechanisms that might underlie animal movements,” Krochmal says. “It seems that turtles learn as youngsters and recall these memories as adults, and they do it by the same cellular mechanisms as humans.”

Krochmal says he and Roth plan to continue the research with hopes of understanding how the brain physically changes after the critical period. This work may someday provide a new window into learning about age-related memory loss and critical periods in humans. Like humans, turtles are a long-lived species. “Conceivably, memory is as important as issue across the species, and conceivably they employ the same mechanism because of this.”

You can see the cover and summary of the paper here:

http://rspb.royalsocietypublishing.org/content/283/1824.cover-expansion

and here:

http://rspb.royalsocietypublishing.org/content/283/1824/20152548