Research Shows Turtles Can Change Shell Color
A national science magazine has highlighted research by Alma College faculty biologist John Rowe and three colleagues that shows turtles can act like chameleons by matching the color of their skin and shells to the color of their base environment.
The story in Natural History Magazine describes how Rowe and faculty colleagues Dave Clark and Larry Wittle plus John Tucker of the Illinois Natural History Survey collected female midland painted turtles and red-eared sliders from the wild, brought them to the lab, and injected them with oxytocin, a hormone that induces egg laying.
Dark- and light-shelled turtles
They assigned the hatchlings to two control groups, which they kept for 160 days on either a white or a black substrate, and to two “reversal” groups, which they kept for 80 days on white or black and then switched to a substrate of the opposite color for another 80 days.
The researchers periodically used a spectrometer to measure the color intensity of spots on each turtle’s head and shell.
By day 80, all the turtles had lightened or darkened, approaching the color of the substrates on which they were living. By day 160, the controls were staying the course, but both reversal groups had switched and were changing to the color density of their new substrate.
That puts freshwater turtles in the same league as chameleons, even if their process of changing colors is much slower, says Rowe.
“Our research goes along with background matching,” says Rowe. “We know that turtles on the clear, sandy bottoms of Lake Michigan are light to match their surroundings, while turtles that live on the dark, mucky bottoms of inland lakes are really dark and blend in to their environment. At first, it appears that there are two separate turtle populations. However, we have found that their color can be induced by the environment in which they live.”
A recent companion study examined whether adult turtles from the wild are capable of changing color. The answer is yes — their color changes when placed in an environment with a different color density, says Rowe.
Rowe includes students in his research on turtle biology. He has created artificial turtle habitats in his laboratory, with students maintaining the lab and analyzing how light intensity affects turtles and their shell coloring and growth rates. Other students accompany Rowe to off-campus sites to study the foraging activity and movements of turtles using radio transmitters.
Posted: Wed, December 23rd, 2009 at 8:24AM