The alligator's massive jaws and powerful tail mark it as a relic of the dinosaur age, a primitive creature that would appear to have little in common with humans. Yet scientists are studying aspects of alligator biology that could lead to new medical treatments and a better understanding of threats to the environment.
In the bayous of Louisiana, researchers have discovered that alligators have a ferocious immune system that can take down a vast range of viruses, bacteria and other infectious microbes, including HIV, the virus that causes AIDS.
And in the lakes and marshes of Florida, they have found that the reptiles are extraordinarily sensitive to pesticides, fertilizers and other pollutants, making them a useful early-warning system of possible hazards to people.
Because of the alligator's potential value to human health, scientists have proposed adding it to the short list of animals whose genes will be sequenced.
"We know so little about the alligator," said Michael Zasloff, dean of research and translational science at Georgetown University Medical Center and an expert on animals' immune systems. "This is an animal that after injury in its swamp, heals. So they can and they should be studied much more extensively to know how a vertebrate in water can experience such severe, terrible injury and recover."
Like the giraffe's neck and the hawk's eyesight, the alligator's immune system is an adaptation to its environment and behavior. Alligators engage in brutal territorial fights in swamps that teem with bacteria and other microbes. After the thrashing stops and the wounded combatants separate, those with the strongest capacity to resist infection tend to survive and can therefore produce offspring.
Mark Merchant, associate professor of biochemistry at McNeese State University in Lake Charles, La., first wondered about the alligator's resistance to disease as a youth, hunting and fishing in the bayous of southeast Texas. So many alligators were missing legs or had deep scars across the belly. Why did they otherwise seem so healthy?
As a scientist, Merchant headed back to the swamps. He snared alligators, drew their blood and returned them to the water. At the lab, Merchant and his team found that alligator blood serum killed all 16 strains of bacteria exposed to it, while human blood serum killed only six. Among the eradicated bacteria were E. coli and strains that cause dysentery, salmonella, and strep and staph infections. Alligator blood also killed the herpes simplex virus and a strain of HIV.
"Their immune system is very, very broad acting," said Merchant, who has published several papers on the subject. "It takes down practically everything. It kills all types of bacteria, many types of fungi and viruses. So it's of great interest to us."
As a growing number of microbes develop resistance to antibiotics, scientists are searching the animal and plant worlds for sources of new drugs. But it's difficult to translate resistance to disease in animals to resistance in people. You can't, for example, cure AIDS merely by injecting alligator blood into a patient.
As a first step, Merchant and other scientists have begun studying the proteins at the heart of the alligator's powerful immune system. They're short chains of amino acids, called peptides, which attack invading microbes.
Zasloff, the Georgetown immune system expert, said several drugs derived from animal peptides are in development, although none has received government approval for use in humans.
Zasloff said that while peptides from alligators and other animals can kill germs in laboratory experiments, they could be toxic in people or they could fail to function without the specific white cells that deploy them in the original animal's body.
"In the test tube, there's no problem," he said. "But in the body we have to worry about whether the anti-microbial peptides will go where they have to go and kill what they have to kill."
The alligator's potential benefit to human health has led scientists to propose sequencing its genome, the long chains of nucleic acids that make up its DNA. The National Institutes of Health's National Human Genome Research Institute has paid for the sequencing of several species that have some bearing on human health or basic biology, such as the fruit fly, Norwegian rat and the mosquito that transmits malaria.
Travis Glenn, a biologist at the University of Georgia who is coordinating efforts to sequence the alligator genome, said the National Institutes of Health turned down a proposal last year but appeared inclined to approve it this year or next.
Despite their stout resistance to what nature dishes out, alligators have turned out to be vulnerable to man-made chemicals. In the lakes and marshes of Florida, biologist Lou Guillette in 1994 found some of the first evidence of chemicals that may be disrupting the reproductive systems of animals and humans.
In Lake Apopka, site of a pesticide spill in 1980, he found male alligators with underdeveloped genitals and female alligators unable to produce healthy eggs. As he expanded his research, he found the same problems among alligators in lakes and marshes that hadn't experienced such a catastrophe, including Lake Okeechobee and the Everglades of western Broward County.
Guillette's work was an early indication of the vast range of pesticides, fertilizers and other chemicals that could obstruct the functioning of hormones. Known as endocrine disruptors, these chemicals interfere with the body's production of the hormones that regulate growth, behavior and the development of sex organs.
These problems were most widespread in lakes and marshes near farms, where pesticides and fertilizers would wash into the alligators' habitat. Guillette, distinguished professor of zoology at the University of Florida, and teams of graduate students have spent years exploring polluted and clean lakes to draw blood samples, examine alligators and collect their eggs. They exposed the eggs to minute amounts of pesticides, fertilizers and other chemicals and found that these substances led to imbalances in estrogen, testosterone and other hormones.
Meanwhile, physicians were recording troubling trends in humans. Using data from the past few decades, they found an increase in testicular cancer, low sperm counts, malformed penises and premature female puberty. Many scientists think the common cause lies in the huge number of chemicals that came into daily life in the last few generations.
"Some of Lou's [Guillette's] early work was really key in bringing attention to this issue," said Elaine Francis, national director of pesticides and toxics research for the U.S. Environmental Protection Agency. "He has consistently demonstrated that this is an ongoing issue that needs to be dealt with."
The EPA plans to screen thousands of pesticides and other chemicals for their ability to disrupt the endocrine systems of people and wildlife. But scientists say it's impossible to pin problems on any single chemical.
"If we can actually show there are problems in these wildlife populations, it raises a flag for our own health," Guillette said. "It doesn't mean that everything we find in wildlife we're going to find in humans, but we have to look at that. If we're finding there are abnormalities in wildlife, we need to address those issues and how we are in fact dealing with the ecosystem and the world around us."
David Fleshler can be reached at firstname.lastname@example.org or 954-356-4535.Copyright © 2015, RedEye