Inter- and intraspecific variability in the copy number of mitochondria in rodents from different elevations of the Ethiopian Highlands

Environmental conditions modulate the energy regimes of organisms, which affects their energetic mitochondrial functions. New regimes may reinforce adaptive increased ATP production, such as in high-elevation mammals, to offset their elevated thermoregulatory costs, increased erythropoiesis, or enlarged lung capacity. ATP production can be increased by higher densities of mitochondria in cells. This study investigated factors affecting inter- and intraspecific variation in the copy number of mtDNA in seven rodent species (genera Stenocephalemys and Lophuromys) from two regions of the Ethiopian Highlands. Quantitative PCR was used to assess the relative quantity of mtDNA (RQ) in liver and muscle tissues (n = 81 specimens). Overall, liver and thigh muscle tissue differed in the amount of mtDNA in a species-, genus- and area-specific manner. All species from the Choqa region had higher RQ in the liver than in the muscle. In contrast, two high-elevation specialists in the Guassa region had a higher number of mitochondria in muscle than in the liver, corresponding to other studies on rodents. In addition, the genus Lophuromys had an overall higher copy number of mtDNA than Stenocephalemys, and the tissue-specific relationship was altitude-dependent, with an absence of difference at high altitudes. This study provides the first data on the mtDNA copy number of Ethiopian rodents and demonstrates the complex relationship of mitochondrial quantity with species, life history, and area of origin.