Seasonal Variation Of Metabolism And Adaptation In Phrynocephalus Vlangalii

Phrynocephalus vlangalii, a species of lizard endemic in China, distributes on Qinghai-Tibet Plateau up to 4500 m above see level. Low temperature and hypoxia are the main features of high land. It is important to study how a ectotherm adatapted to such a harsh environment. In this study, seasonal variation (spring, summer and autumn) in body weight and visceral organ weight, preferred body temperature, standard metabolic rate (SMR), mitochondrial respiration rates, activities of four metabolic enzymes and contents of five metabolites were examined in P. vlangalii. Our results showed that body weight and visceral organ weights of lizards had significant difference with the seasonal variation, usually they reached the maximum in autumn. The results showed that the preferred body temperature of lizard was low in spring, intermediate in autumn and high in summer. SMR, maximal mitochondria! respiration rate and cytochrome c oxidase (CCO) activity of liver and skeletal muscle were the highest in spring and the lowest in summer between different seasons. From the analysis of metabolic enzyme activity, three metabolic enzymes activities with the seasonal variations showed significant difference. Lactate dehydrogenase (LDH) activities of liver and skeletal muscle had higher during spring in comparison to other two seasons, but there was no difference in summer and autumn. LDH is the key enzyme of anaerobic metabolism, the reason for this phenomenon may be closely related to glycolysis supplies most of the ATP used by reptiles during short periods of intense activity. Citrate synthase (CS) activities of liver and skeletal muscle were the highest in spring, summer in the middle value and the enzyme activity is the lowest in autumn. However, compared with other two seasons, β-hydroxyacyl coenzyme A dehydrogenase (HOAD) activities of liver and skeletal muscle were the highest in autumn. When analyzed contents of five metabolites, we found they had significantly changed in different seasons, and there were a distinct tissue specificity with their variations, In the three active seasons, protein contents of serum, liver and skeletal muscle were the highest in summer in comparison to other two seasons. Glucose content of liver was the highest in autumn, and it was about higher 3 times and 1.4 times than in spring and summer respectively, but there was no significant difference in skeletal muscle between seasons. Similarly, glycogen content of liver was particularly high in autumn, and it was about higher 8 times and 2 times than in spring and summer respectively. Glycogen content of skeletal muscle was higher in autumn than in spring and summer, but there was no significant difference between spring and summer. Free fatty acids contents of the serum and liver were much higher in summer and autumn than in spring, but there was no significant difference in muscle tissue between seasons. The content of triglyceride in serum and liver increased gradually with the spring, summer and autumn, but there was no significant difference in muscle tissue between seasons. From above results, we found lipid metabolism of P. vlangalii was relatively strong and glycogen content increased greatly in autumn. It indicated that anabolism of carbohydrate and catabolism of lipid enchanced in autumn, this may be associated with hibernation of lizards. On the whole, seasonal variation of metabolism is the highest in spring, summer in the middle value and the metabolism is the lowest in autumn. Seasonal variation of metabolism is the opposite of preferred body temperature, this may be one of the mechanisms to adapt to the environment in P. vlangalii. But seasonal variation of metabolism and the relationship between the environment adaptation in P. vlangalii remain to be studied further.