Physiological and biochemical basis of basal metabolic rates in Brandt's voles (Lasiopodomys brandtii) and Mongolian gerbils (Meriones unguiculatus)

Basal metabolic rate (BMR) has been shown to be a highly flexible phenotypic trait both between and within species, but the physiological, biochemical and molecular mechanisms are still unclear. Brandt's voles (Lasiopodomys brandtii) and Mongolian gerbils (Meriones unguiculatus) are two sympatric rodent species in Inner Mongolian grasslands of China. It has been shown that Brandt's voles have higher metabolic rate than Mongolian gerbils. In this study, we elucidated the inter-specific variation in BMR integratively from the molecular levels to whole organism. Our results showed that differences in organ mass were not good predictors for the observed variations in BMR, while variations in the activity of thyroid hormones and the metabolic biochemical markers of tissues, such as mitochondria density, cytochrome c oxidase activity and state 4 respiration, were strongly correlated with variations in BMR, and there was also a positive relationship between residuals of T3/T4 and state 4 respiration, suggesting that thyroid hormones play an important role in the determination of BMR variations.