Although Ohio may not be known for containing exotic wildlife, Miami University senior research scholar Jon Costanzo’s lengthy study of the wood frog shows that the creatures present some unique adaptations.
As a cryobiologist, or a biologist who focuses specifically on animals existing at low temperatures, Costanzo has spent the last 25 years exploring the ability of the wood frog, known as rana sylvatica, to freeze solid during the winter and thaw to return back to life when spring arrives.
Costanzo headquarters his research at Miami, but he recently traveled to Alaska, along with three graduate research assistants, to study the wood frog in even more extreme temperatures than those of Ohio. His exploration into the formation of frogs into, essentially, an ice cube, presents evolutionary adaptations and show the resilience of nature.
Beginning the study in 1989, Costanzo has gradually uncovered the internal processes that the wood frog undergoes to allow it to survive freezing and resume its usual habits upon thawing. In order to freeze, the wood frogs begin dehydrating their inner organs, expelling all water in order to form a coating around themselves. Organs, as well as the frogs’ blood streams, are frozen solid. Their hearts cease to beat, their brain function stops and no oxygen reaches their muscles or organs for the entirety of their icy hibernation. This absence of oxygen, known as a “metabolic depression”, requires the frog to utilize various bodily chemicals, such as glucose and urea, to initiate an anaerobic metabolism without oxygen that will still allow it to fuel and preserve its cells until warmer temperatures arrive.
This tiny species of frog has therefore found a way to cheat death and extreme conditions by literally putting itself on ice. Such an adaptation is even more amazing when one considers the range of temperatures it can withstand. The frogs’ habitat ranges across the eastern USA, and across Canada and Alaska. They can be found as far south as the mountains of Georgia and into the outer parts of the Arctic Circle in Canada. In Ohio, Costanzo’s research has found that the frogs can withstand being frozen down to temperatures of about 4 degrees Celsius, or 39 degrees Fahrenheit, while in Alaska the frogs can survive being frozen as low as -16 degrees Celsisus, or 3.2 degrees Fahrenheit.
The most miraculous aspect of this adaptation is the frog’s ability to simply bounce back once spring arrives. Due to the chemicals it uses to preserve some metabolic process during freeze, once thawed it can immediately begin activity to find food and search for a mate rather than being exhausted and vulnerable to prey.
Costanzo has discovered other freeze tolerant species, some of which are also found in Ohio, such as the box turtle, which he studied in the early 1990s. The evolution of such an adaptation across species fascinates Costanzo.
“They’re fascinating because these species have all arrived at the same solution to a common challenge different points of origin,” he says.
Costanzo plans to continue his research on the wood frog for the remainder of his time as a research scholar at Miami, with plans to return to Alaska to examine the wood frog at even colder temperatures. There is still much left to uncover about how life forms throughout the biosphere have adapted to the extreme conditions our environment can present.