If a human being sat at the bottom of a slough all winter, that person would freeze and die.
Painted turtles sit at the bottom of sloughs all winter, and they may freeze, too. But they don't die. In spring, they thaw out.
What is it about a turtle's physiology that is so different that allows this seemingly miraculous thaw to happen?
That is a question Tim Muir, assistant professor of biology at Augustana College, has been investigating for years, conducting research on turtles hatched from eggs he collects from turtles in the slough that runs through the Rock Island campus.
He will share what he's learned so far and answer questions on Wednesday and Saturday, June 7 and 10, when he conducts one of this year's eight Riverine Walks sponsored by River Action Inc., a Davenport-based environmental organization.
Muir might also touch on the implications that his research could have on the future of human organ donations. At present, harvested organs remain usable for only a certain length of time; if they could be frozen, then successfully thawed, they would be available for longer periods.
Other Riverine topics to be presented by local professionals include the story of Davenport pioneer leader Antoine LeClaire, archaeological sites near the mouth of the Rock River, recycling, raising butterflies and bald eagles. Participants will meet at various locations for the guided walks.
People attending Muir's talk — titled "I'm freezing out here!" — will begin in his lab at Augustana to see the turtle eggs that he begins harvesting in late May into June.
The eggs turn into hatchlings and, in time, are subjected to cold temperatures — sometimes gradually, sometimes in intense bursts, just as would happen in nature. Then their organs are harvested and researchers measure certain compounds present in the brain, liver and blood to try to determine how the turtle survives.
After viewing the lab, participants will walk down to the slough to talk about the three basic winter strategies adopted by animals that live in the Quad-City region.
Some birds, for example, leave, migrating to warmer climates.
Other birds and mammals hunker down in sheltered areas, relying on their coats of fur or feathers and a steady supply of high-calorie food.
But the vast majority of creatures — all fish, reptiles and amphibians such as turtles, snakes, frogs and salamanders and nearly all insects — adapt to the cold, Muir said. Some enter a kind of hibernation state, while many insects morph into a different life cycle, such as the egg or larval stage, living in a nook, or underground, where they do not freeze.
Painted turtles in the slough not only can freeze and then thaw, but they can survive without breathing for months as the water above them freezes. "They can hold their breath for that long," Muir said. "It is amazing."
Despite his years of research, Muir still does not know for sure how the turtles survive, although the phenomenon may be linked to high levels of sugar and urea in their blood. Cold temperatures may act as a trigger for the turtle to produce more sugar and urea.
"The more concentrated stuff there is in a liquid, the lower its freezing point, Muir said. That is why salt is applied to roadways during times of freezing rain.
"It's really interesting how animals survive in stressful environments," he said. "How they conserve energy, how they survive temperature extremes when they aren't eating."