Andis Arietta, left, and Yara Alshwairikh collect DNA samples from wood frogs in the Alaskan Arctic. Photo by Kaylyn Messer.
I am deep in the Alaskan Arctic, 300 miles from the nearest road system, attempting to conduct the kind of science that usually requires a specialized laboratory. We rowed 30 miles of meandering flatwater today, bringing our total to 200 river miles in 12 days since we landed at a lonely gravel bar on the headwaters of Ambler River in Gates of the Arctic National Park.
Mosquitoes spangle the tent canopy arching over me. Backlit by summer solstice sun, the silhouettes of the insects make an inverted night sky of shifting constellations. The sun never sets on the banks of the Kobuk River this time of year. It hangs high above the horizon even now at 11 p.m., transforming my tent into a solar oven as I, ironically, work to uncover the secrets of a frog that can turn into ice.
Wood frogs are one of the few amphibians found in Alaska, and they are the only frog found north of the Arctic Circle. During winter, most frogs hibernate by burying themselves below the frost line—an impossibility in the land of permafrost. Instead, wood frogs have developed the ability to survive winter as solid blocks of ice, only to reanimate as if from a brief nap in the spring. Scientists have fixated on this sci-fi-esque ability for decades. We now understand much of the mechanics of freeze-tolerance: frogs replace the water in their cells with a kind of organic antifreeze and systematically shut down their organs to retain blood flow to vital tissue until the moment before their bodies crystalize.
Yet, many of the details of how wood frogs undergo this statis and subsequent reanimation remain mysterious. Illuminating this process could hold major benefits for human health. For instance, one day we may be able to apply the wood frog’s powers to freeze organs for human donor transplants and prevent clots. Clues to reverse engineer the wood frog’s freezing ability could be hidden within their genetic code. Additionally, wood frog DNA may offer insights into long-standing questions in evolutionary biology and questions about how wildlife will adapt to climate change.
My lab mate, Yara Alshwairikh, and I took up the challenge of unlocking the genetics of these enigmatic frogs for our respective dissertations at Yale University. Despite over a century of wood frog research, tissue samples needed to recover DNA are difficult to find, especially from frogs in the most northern parts of the range. So we traveled across the continent in search of frogs to fill in the gaps on the map.
But searching for a miniscule frog in a million-acre wilderness is daunting. Looking at satellite images through the eyes of a frog helps. Wood frogs like to avoid ponds with fish. So we looked for the smallest pools visible on satellite images, avoiding the towering cut banks and aiming for ponds that required the least amount of bushwhacking. In waders, bug nets, and gloves, we carefully scanned the margins of ponds for hints of movements and seined the water with nets in search of tadpoles.
Once the frogs were captured, we collected organ and other tissue to preserve the DNA; a straight-forward process in the lab, but far more tedious in the field—swapping lab coats for rain jackets and lab benches for sleeping pads wrapped in trash bags.
Back at the University, it took about a day to extract DNA from just a sliver of tissue. The DNA was sent to a sequencing facility and returned to us as an enormous datafile. Just opening these files would melt a home computer. Instead, we funneled our data into super computers to allow us to analyze the genomes and look for key differences between populations or areas of the genome that associate with specific traits.
Searching for the secrets of icy adaptations among masses of genomic data is a lot like looking for a needle in a haystack or an inch-long frog in the Alaskan wilderness. But like the course of the Kobuk, the process of scientific discovery is a long and meandering path. Months of analysis lay before us, and many researchers will build on our work. With luck, the tiny frogs of the Arctic will enable breakthroughs in medical and ecological science.