Moose Bones Yield Clues to Age-old Affliction
by Jennifer Donovan
As a 150-pound person ages, the aches and pains of osteoarthritis—a degenerative and progressively crippling joint disease—often become an unpleasant fact of life. Think how the same condition feels to a thousand-pound moose.
In a report published in Ecology Letters in September 2010, Michigan Tech wildlife ecologists Rolf Peterson and John Vucetich; Thomas Drummer, professor of mathematical sciences; and colleagues in Minnesota and Ohio identified a link between malnutrition early in a moose's life and osteoarthritis as the animal ages.
"I've long thought that there was a nutritional link to the increase in osteoarthritis in moose on Isle Royale as the population of the animals grew in the 1960s and 1970s," says Peterson, who holds the Robbins Chair in Sustainable Management of the Environment. He even raised the question in a paper published in the Journal of Wildlife Diseases in 1988, a hypothesis that was largely ignored.
Three generations of wildlife ecologists have been studying the moose of Isle Royale, a wilderness island national park in northwestern Lake Superior, and their primary predators, wolves, for more than fifty years. A key factor in the study has been the analysis of the bones of dead moose.
During the first two decades of the study, the scientists found increasing evidence of osteoarthritis in moose bones on Isle Royale, mostly in the animals' hip joints and lower spine. This type of arthritis is identical to the kind that affects humans and many other mammals.
Unlike the damaged and partial skeletons more commonly recovered from archeological digs, the bones of moose that die in the wilderness setting of Isle Royale usually reveal details such as gender, age, and degree of osteoarthritis. And they often include metatarsal leg bones, which are extremely sensitive to prenatal nutrition.
"After birth, the mass of a moose increases thirty-fold, but when a moose is born, the metatarsus is already half grown," Peterson explains. That gives them a leg up for running fast to escape their predators, the wolves.
Matching the length of a moose's metatarsal bone with the degree of osteoarthritis found in the hip joints and spine provided Peterson and his team with their best evidence of a nutritional link to osteoarthritis.
They found that the moose with the shortest metatarsal bones—indicating poor early nutrition—were the ones more likely to develop osteoarthritis later in their lives. They also observed the highest rates of osteoarthritis in moose born in years when the moose population was the largest and nutrition most problematic. As the moose population declined, improving the availability of adequate nutrition, osteoarthritis declined among the better nourished moose as they aged.
"This physiological association also has ecological implications," says Peterson. "The debilitating effects of osteoarthritis would inhibit a moose's ability to kick or dodge a lunging wolf. Consequently, the incidence of osteoarthritis is associated with the rate at which wolves kill moose on Isle Royale."
The ecologists' findings about nutrition and osteoarthritis in moose have implications for understanding arthritis in humans, Peterson goes on to say. Studies of humans and other animals have increasingly linked many chronic adult diseases with nutritional deficiencies early in life.
"Our study suggests the need to consider more carefully whether osteoarthritis is like other late-onset pathologies, including heart disease, diabetes, and hypertension, that appear to have risk factors established early in life," he observes. "The apparent link between early nutrition and osteoarthritis indicates that the cause of osteoarthritis is more complex than commonly assumed."
The association between osteoarthritis and early malnutrition also could help explain anthropologists' observation that arthritis became more prevalent in Native Americans as their diet became poorer, due to an increased reliance on corn and agriculture and less on hunting and gathering, the scientists suggest.
The research on early nutrition and arthritis in moose was supported by the National Science Foundation, the National Park Service, and Earthwatch Inc.