Relationship Between Organ Masses and Basal Metabolic Rate (BMR) in Tree Sparrows (Passer montanus)

Abstract BMR (basal metabolic rate), body mass and organ masses of tree sparrows (Passer montanus) were measured to analyze the correlation between organ masses and BMR in tree sparrows, and to evaluate the underlying physiological causes of difference in BMR. Adult tree sparrows were live-trapped by mist net in Qiqihar City, Heilongjiang Province (47°29′N, 124°02′E). The closed circuit respirometer was used to measure the metabolic rate (MR), and controlled the ambient temperature by using a water bath (±0.5°C). Body masses were measured to the nearest 0.01 g before and after BMR measurements with a Sartorius balance (model BT25S). The mean value was recorded as body mass. Wet and dry masses of several organs were measured, too. BMR was (4.276± 0.385) mL O 2 /(g · h) and mean body mass was (18.522±0.110) g. Since not all the variables were normal distributed, a log 10 -transformation of those variables was employed to linearize them, prior to analyses. Simple regression analyses indicated that most organ masses showed a significant high correlation with body mass. Both the small intestine and rectum masses were notable exception to that trend. The body-mass-adjusted residual analysis showed that only the kidney wet mass, brain mass, stomach mass, small mass and rectum wet mass correlated with BMR. In addition, correlations between several organ masses and BMR were observed. Because of the inter-correlations of organ masses, a principal component analysis (PCA) was performed to redefine the morphological variability. The first four components whose eigenvalues were greater than 1 could explain 75.2% variance of BMR. The first component, whose proportion reached 30.19%, was affected mainly by stomach mass, small intestine mass and rectum mass. Therefore, the results supported the hypothesis that BMR was controlled by some “expensive metabolic” organs.