For decades now, Chi-Hing "Christina" Cheng has been lured by Antarctica in a quest for the cold facts about the fishes of the Southern Ocean.
She is hooked on uncovering the genetic mysteries of the antifreeze protein that allows these fish —the Antarctic notothenioids -- to thrive in the world's coldest, harshest marine environment.
"We want to figure out how the antifreeze protein genes evolved in this isolated, freezing environment," says Cheng, an AAAS Fellow and associate professor of animal biology at the University of Illinois. "This is one of the few clear examples in biology where the environmental driving force can be directly linked to the evolution of a survival trait."
Through the National Science Foundation's Division of Polar Programs, Cheng and her team study the evolutionary traits of the Antarctic notothenioid at McMurdo Station, a former naval outpost, now a modern research facility.
Cheng first ventured to the Antarctic as a physiology graduate student working for Arthur DeVries, who discovered the antifreeze protein in the late 1960s.
"What a unique place," she recalls. "It was an amazing experience — I got sucked in."
Cheng and DeVries would eventually discover they shared more than an interest in Antarctic antifreeze (and the basement of Burrill Hall on the U of I campus). The two were married in 1986, and the Antarctic became their home away from home.
Once a more welcoming place, the Southern Ocean long ago played host to an abundant diversity of marine fish. But when Antarctica water froze about 15 to 20 million years ago, almost all but the notothenioid died out.
Armed with the protective antifreeze protein, the notothenioid ancestor survived, thrived and diversified in a wide open ocean with very little competition.
Though they are all related, the five families of Antarctic notothenioids, comprising about 100 species, bear little family resemblance. The most unique is the ghostly icefishes, the only vertebrate on Earth with no red blood cells. Cheng's favorite is the Antarctic toothfish, which can grow to hundreds of pounds, and makes a reliable subject for her studies.
The freezing point for the blood of these Antarctic fish is -1 degree Celsius, but they survive and thrive in water that's -2 degrees Celsius. As Cheng says, "Theoretically, they should freeze and die."
In spite of ice crystals that float freely inside their bodies, the antifreeze protein keeps the fish's body fluids in a liquid state.
"Ice crystals get in continually, but the antifreeze binds to them and prevents them from getting any bigger," says Cheng.
"Nobody had any idea a protein could interact with an external substance like ice crystals in that way — how creative!" says an admiring Cheng. "Antifreeze research has so many different facets. The questions are never ending and always interesting."
One of the questions she finds most intriguing is how the new antifreeze gene was created. Rather than copying and making use of the entire ancestral gene, as is usually the case, it seems the ancestral Antarctic notothenioid did something unexpected.
"The fish used just a tiny bit of protein coding sequence from the ancestral gene. The business end of the new gene was just about created from scratch, by repeatedly duplicating that tiny bit," explains Cheng. "It's a new twist on the traditional notion of new gene creation."
To fully understand whole animal evolution of cold adaptation, Cheng has recently embarked on whole genome sequencing of the Antarctic toothfish.
Her own evolution is no less surprising to Cheng, who was born in China and moved with her family to Hong Kong at the age of six. As a teenager, she made her way to the U.S. to attend college in Texas.
"When I left Hong Kong, I started this long journey, which has just been amazing," says Cheng. "I've come to value the freedom and opportunities we have in this country to pursue learning based on curiosity and passion."
Still, those early days were anything but easy.
"We were very poor — it was difficult for me to come here for college," recalls Cheng, the middle of seven children. "There were a lot of hopes and dreams riding on my shoulders."
Those pressures propelled her to complete her undergraduate degree in just two-and-half years. As she says, "I thought the quicker I finished, the less burden I would be on them."
It is the burden humanity is placing on the planet that concerns Cheng these days. She has, after all, seen firsthand the effects of global warming and commercial fishing in Antarctica.
"I take an evolutionary view. Of the millions of known animal species, we [humans] are the tiniest, newest twig on the Tree of Life," she says. "Species come and go a lot ... Who can say if human beings will be around forever or if we are accelerating our own demise?"
Perhaps it is an ancient fish's ability to change that gives her hope for us all.