Pre-hibernation energy reserves and their consumption during freezing in the moor frog Rana arvalis in Siberia

Abstract

For the first time, the pre-hibernation sizes of “storage” organs (liver and fat bodies), the type, concentration and total content of reserve substances (glycogen or lipids) in these organs and muscle tissue, and their change during freezing in freeze tolerant specimens of the moor frog (Rana arvalis) in the Siberian population were studied. In autumn, the relative weight of the liver (hepatosomatic index) in the studied individuals reaches 10%, which is 2–4 times higher than in most species of Eurasian ranid frogs; this determines 2–4 times greater hepatic glycogen stores. The concentration of glycogen in the muscles is about 4.4 times lower than in the liver, but the total storage of glycogen in the muscles is 43–57% of the storage in the liver. The high degree of glycogen degradation upon freezing in both tissues may indicate that it is promising to search for either high levels of glucose or other cryoprotectants than in the ranid frogs studied so far. The content of lipids in the tissues in autumn is small and not completely consumed before freezing. Probably, lipids play an insignificant role in pre-winter metabolism, and are necessary for maintaining activity after overwintering. Thus, the highest freeze tolerance of the moor frog among the Eurasian ranid frogs (−14°C to −16°C in different Siberian populations) may be due to the high relative weight of the liver, which provides a large supply of glycogen before hibernation, the participation of muscle tissue in the deposition of almost a third part of all glycogen the body, significant consumption of glycogen during freezing for cryoprotectants. The patterns of storage and consumption of pre-hibernation energy resources in frogs of the genus Rana differ greatly not only between terrestrial and aquatic hibernators but also between freeze tolerant species.