Turtle Expert

John Iverson retired last year, but his 30-plus year research with painted turtles of Nebraska must go on.

To continue the study, Iverson received nearly $105,000 of a total $724,000 grant from the National Science Foundation. The project, entitled “Climate change and environmental sex determination in a geographically-widespread species” will involve two-three students for 10 weeks each summer for the next three years.

“The thrust of this grant is TSD or temperature dependent sex determination,” Iverson says. In a lab setting, researchers have proven that the temperature of the nest during the middle third of the incubation determines the sex of painted turtles. Hot nests produce females, while cold nests produce males.

“This can be easily predicted in a lab, but in the field the temperatures of a nest fluctuate a lot,” he says. “What we are hoping is to build a model that can predict the sex ratio of painted turtles based on local climate data across their range.”

The grant allots about $100,000 each to fund research at seven sites including Iverson’s Nebraska site, and sites in Illinois, New Mexico, Washington, Minnesota, Kansas and Idaho.

“We wanted geographic variation with the seven sites,” explains Iverson, professor emeritus of biology. “The Illinois site is obviously colder, and the New Mexico site is hotter. We hope we have enough variation to correctly predict and test these models.”

Iverson says that perhaps the larger question that the grant hopes to answer concerns climate change.

“If we are getting warmer, what is this going to mean to this particular species?” he says. “If warmer temps mean more females, do we get to the point of where no males are produced, and then will TSD turtles become extinct? If it happens too fast we could lose a lot of species.”

Long-term study

Iverson began collecting data from the site in Nebraska in 1981.

“We’ve also been piloting the program in New Mexico, Washington and Minnesota, and we have added Kansas and Idaho, but we have no data from those two sites,” he says. “We are on the forefront in this study because we have been collecting data from (Nebraska) for so many years.”

Just before coming to Earlham in 1978, Iverson and a couple of friends took a 9,000-mile trek to visit and learn about possible research sites in the United States. Then in 1980 he revisited two or three sites from that original excursion.

“I picked the most remote site,” he says. “The Nebraska site hadn’t changed in essentially 200 years except that the buffalo have disappeared and cattle have replaced them. The Nebraska site is on a remote refuge about 28 miles down a single lane dirt road. We are really out there, but the wildlife is spectacular and the turtle population is fantastic. This will be my 33rd year of collecting data from this site.

“I set out to study the general ecology of all turtles. With the number of turtles that we caught, it was such a productive site and such a perfect site to use as a teaching and research tool that I just kept coming back.”

Throughout the study, Iverson says he has involved students in every way possible. Iverson teaches students how to catch, measure and weigh turtles. Transmitters are installed to allow better tracking, and recently the research groups have conducted paternity testing through blood samples.

“We are still catching turtles that we caught in 1981 that were full adults in 1981, and they haven’t changed in size, shape or weight in 30 years.”

Iverson says the study and its length of duration exists because of Earlham’s emphasis on faculty-student collaboration.

“This study would only have been possible at a small college like Earlham that values student faculty interaction and can support faculty and student projects for long periods of time,” he says. “NSF rarely supports long-term studies because they want a product quickly. You have to be at a place that values long-term student-faculty research. The system we have here at Earlham enables this to happen.”

John Iverson
John Iverson, Professor Emeritus of Biology

Ph.D., University of Florida; M.S., University of Florida; B.A., Hastings College

Print Friendly and PDF