Meeting Abstract
Many animals can lower their metabolic rate to conserve energy during changes in diet. This phenomenon is widespread across vertebrates, but the responsible mechanisms are not well understood. It is thought that animals achieve a hypometabolic state by reducing the mass of energetically-costly organs, but reduced mitochondrial activity could also play a role. We assessed the impact of diet on digestive physiology and metabolism in three species of rodents with different natural diets: grasshopper mice (Onychomys torridus; insectivore), white-footed mice (Peromyscus leucopus; omnivore), and montane voles (Microtus montanus; herbivore). Rodents were placed on either a high-fiber (37%) or low-fiber (12%) diet for 5 weeks, after which we measured resting metabolic rates via open-flow respirometry and weighed energetically-costly tissues, such as heart, gut, liver, and kidney. O. torridus fed high-fiber diets had significantly reduced metabolic rate, but P. leucopus and M. montanus did not. Interestingly, O. torridus on high-fiber diets exhibited greater gut masses and, opposite of our expected result, larger kidney masses. P. leucopus and M. montanus had significantly larger kidneys on high-fiber diets. Further, O. torridus on high-fiber diets exhibited higher mass-specific mitochondrial activity (measured by citrate synthase activity) in liver tissue, despite no significant differences in liver masses. These results suggest that rodents with different natural diets employ divergent mechanisms to compensate for sub-optimal diets, and that metabolic depression involves more than a reduction in organ size.
