Senescence related pathologies in moose (Alces alces) bones: why do some moose wear out their teeth faster or slower given their age?

The foundation of life history theory posits that organisms will allocate energy or make trade-offs between traits throughout their lifetime to optimize reproductive success. According to the disposable-soma theory, organisms have a finite amount of energy to invest and as energy is invested, less is available for somatic maintenance and repair later in life which ultimately leads to earlier or more rapid senescence. In this study I endeavor to answer the question: why do some moose wear out their teeth faster or slower than others? I used data on tooth wear in 1112 moose collected over 50 years in Isle Royale National Park to identify what individual and cohort factors influence rates of tooth wear in moose and I evaluate evidence for the disposable-soma theory. Using a two-step approach, I first built and compared a set of linear models that predicted tooth height from age at death and sex. The most parsimonious model includes both age and sex and from that model I calculated the residuals. I then built subsequent mixed models to determine how much of the variance seen in the residuals was explained by year of birth as an indicator of cohort effects. Here I found that cohort effects explain none of the variance we see in rate of tooth wear in moose. I then built a set of linear regression models to predict rates of tooth wear from body size, gum recession (periodontal disease) and presence/absence of arthritis. Based on AIC, the best model included body size and the interaction between body and gum recession (R2=0.032). These results provide evidence that supports the disposable-soma theory as an explanatory mechanism for the evolution of senescence in vertebrates