Links between three chronic and age-related diseases, osteoarthritis, periodontitis, and osteoporosis, in a wild mammal (moose) population.

OBJECTIVE: Osteoarthritis, periodontitis and osteoporosis are chronic, age-related diseases which adversely impact millions of people worldwide. Because these diseases pose a major global public health challenge, there is an urgent need to better understand how these diseases are interrelated. Our objective was to document the age and sex-specific prevalence of each disease and assess interrelationships among the three diseases in a wild mammal (moose, Alces alces) population. METHODS: We examined the bones of moose dying from natural causes and recorded the severity of osteoarthritis (typically observed on the hip and lowest vertebrae), osteoporosis (osteoporotic lesions observed on the skull) and periodontitis (observed on maxilla and mandibles). RESULTS: Periodontitis was associated with a greater prevalence of both severe osteoarthritis and osteoporotic lesions in moose. We found no evidence to suggest that moose with osteoporotic lesions were more or less likely to exhibit signs of osteoarthritis or severe osteoarthritis. The prevalence of osteoarthritis, periodontitis and osteoporotic lesions was greater among males than for females. CONCLUSIONS: Our results were consistent with the hypothesis that bacterial pathogens causing periodontitis are a risk factor for osteoarthritis and osteoporosis. They are also consistent with the hypothesis that the inverse association between osteoarthritis and osteoporosis sometimes observed in humans may be influenced by shared risk factors, such as obesity, smoking or alcohol consumption, which are absent in moose. Together these results provide insights about three diseases which are expected to become more prevalent in the future and that cause substantial socio-economic burdens.

The influence of winter severity, predation and senescence on moose habitat use.

Habitat use is widely known to be influenced by abiotic and biotic factors, such as climate, population density, foraging opportunity and predation risk. The influence of the life-history state of an individual organism on habitat use is less well understood, especially for terrestrial mammals. There is good reason to expect that life-history state would affect habitat use. For example, organisms exhibiting poor condition associated with senescence have an increased vulnerability to predation and that vulnerability is known to alter habitat use strategies. We assessed the influence of life-history stage on habitat use for 732 moose (Alces alces) killed by wolves (Canis lupus) over a 50-year period in Isle Royale National Park, an island ecosystem in Lake Superior, USA. We developed regression models to assess how location of death was associated with a moose's life-history stage (prime-aged or senescent), presence or absence of senescent-associated pathology (osteoarthritis and jaw necrosis), and annual variation in winter severity, moose density and ratio of moose to wolves, which is an index of predation risk. Compared to senescent moose, prime-aged moose tend to make greater use of habitat farther from the shoreline of Isle Royale. That result is ecologically relevant because shoreline habitat on Isle Royale tends to provide better foraging opportunities for moose but is also associated with increased predation risk. During severe winters prime-aged moose tend to make greater use of habitat that is closer to shore in relation to senescent-aged moose. Furthermore, moose of both age classes were more likely to die in riskier, shoreline habitat during years when predation risk was lower in the preceding year. Our results highlight a complicated connection between life history, age-structured population dynamics and habitat-related behaviour. Our analysis also illustrates why intraspecific competition should not be the presumed mechanism underlying density-dependent habitat use, if predation risk is related to density, as it is expected to be in many systems.

Mercury, lead and lead isotope ratios in the teeth of moose (Alces alces) from Isle Royale, U.S. Upper Midwest, from 1952 to 2002.

Assessing the effect of recent reductions in atmospheric pollution on metal concentrations in wildlife in North America has been difficult because of the sparse availability of historical samples with which to establish a "pre-regulation" baseline, and because many ecosystems may be affected by local point sources which could obscure broader-scale trends. Here we report a recent 50 yr annual record of Hg, Pb and Pb isotope ratios in the teeth of a resident population of moose (Alces alces) in Isle Royale National Park, a relatively remote island in Lake Superior, Michigan, USA. During the early 1980s, concentrations of tooth Hg abruptly declined by approximately 65% compared to the previous 30 years (p<0.001), similar to a previous study of Hg in herring gull eggs in the Great Lakes region. Lead declined at the same time, and by 2002 Pb in adult moose teeth was approximately 80% lower than it had been prior to the early 1980s (p<0.001). These trends were unaffected by normalization against the geogenic elements La and Sr, which indicates that the trends in Hg and Pb had an anthropogenic cause. Temporal patterns of Pb isotope ratios suggested that the primary sources of Pb at different times in the moose were combustion of U.S. coal and leaded gasoline. Reductions in emissions from coal combustion might explain the co-incident reductions of Hg and Pb in Isle Royale moose, with elimination of alkyl Pb additives also playing a role in the continued tooth Pb reductions after 1983.

Tooth fracture frequency in gray wolves reflects prey availability.

Exceptionally high rates of tooth fracture in large Pleistocene carnivorans imply intensified interspecific competition, given that tooth fracture rises with increased bone consumption, a behavior that likely occurs when prey are difficult to acquire. To assess the link between prey availability and dental attrition, we documented dental fracture rates over decades among three well-studied populations of extant gray wolves that differed in prey:predator ratio and levels of carcass utilization. When prey:predator ratios declined, kills were more fully consumed, and rates of tooth fracture more than doubled. This supports tooth fracture frequency as a relative measure of the difficulty of acquiring prey, and reveals a rapid response to diminished food levels in large carnivores despite risks of infection and reduced fitness due to dental injuries. More broadly, large carnivore tooth fracture frequency likely reflects energetic stress, an aspect of predator success that is challenging to quantify in wild populations.