The pigs' domesticated forebears were brought to the island in the early 1500s by the Spanish, but they have since turned wild. They roam freely and feed on acorns, but the acorn crop on the island follows a "boom or bust" pattern both within years - with the acorns dropping only in the fall - and between years. When acorns are scarce, the pigs stray into the island's salt marshes to dig for roots.
All the Ossabaw pigs that I. Lehr Brisbin of the Savannah River Ecology Laboratory has tested so far show signs of a "metabolic syndrome" or "pre-diabetes". Just like humans with diabetes, when the pigs become sedentary they accumulate fat around their midriff and their blood glucose levels rise, as do their blood cholesterol and blood pressure.
Normally, however, the pigs are highly active and lean. They exhibit none of the symptoms of diabetes, nor of the related cardiovascular disease, and Brisbin suspects that the condition allows them to survive years when the acorn crop is poor.
"The metabolic syndrome means that you have a certain set of metabolic and biochemical characteristics that allows you to rapidly and efficiently lay on piles of fat when times are good and then use them when times are lean," he said at the annual meeting of the Ecological Society of America. "That same syndrome in humans, because we are constantly in a time of plenty, thank you to the Big Mac and super-sizing, means we just stay fat."
According to Brisbin, the metabolic syndrome is the downside of the so-called "thrifty genotype", a genetic predisposition to obesity that evolved in times when food was less constantly plentiful and starvation a real risk. In both humans and pigs, genes that predispose toward obesity would have been selected for because only those animals that survived lean periods by virtue of having it would go on to reproduce.
So why do the pigs get away with perfect health while the human cases of type II diabetes soar? "We think the answer is exercise," says Brisbin, adding that the experiments he refers to as "Project Couch Potato" have yet to be done. "We need to take Ossabaw pigs in the woods, put them in pens so they can't exercise, and stuff them with high cholesterol diets to see if they can act like people metabolically."
Since the pig cardiovascular system is very similar to the human one, the biomedical community is getting excited about the prospect of studying the Ossabaw pigs as a model of human type II diabetes. The incidence of type II diabetes in the US has breached epidemic proportions, and at the moment, no good models of the disease exist. There are rat models of diabetes, but the rodent cardiovascular system differs significantly from our own.
Brisbin's colleague Michael Sturek of the University of Missouri is trying to raise funds to pursue those studies, but meanwhile the Ossabaw pigs are vanishing thanks to the efforts of hunters and the Georgia Department of Natural Resources, which has a pig eradication program underway on the island.
BioMedNet
7 August 2003
Original web page at BioMedNet
