A Study On Cold Hardiness And Its Mechanism Of Two Toad-headed Lizards Living At Different Altitude

Cold,hypoxia and intense UV radiation are three major environmental challenges of organisms living at high altitudes.However,lifelong exposure to high altitude could generate certain adaptability which makes them tolerant to these environments.Phrynocephalus erythrurus inhabits the Qiangtang Plateau in northern Tibet,and is believed to be the world's highest lizard.The aim of the present study was to investigate survival strategies under low temperature and the possible mechanism of Phrynocephalus erythrurus.We collected the Phrynocephalus erythrurus living at Tanggula town of Golmud city of Qinghai Province and choose the Phrynocephalus przewal skii living at Minqin County of Gansu Province as the reference.To compare the physiological and biochemical indexes of two altitude lizards before and after hibernation,include supercooling ability,the abilty to resist incolutive freezing,the concentration of hemoglobin and hematocrit,four organic osmolytes(such as glucose,urea,lactate and glycerol)that may acted as cryoprotectants etc.The results showed that there has no difference of supercooling ability of two species.But the ability to resist inc olutive freezing of Phrynocephalus erythrurus was signif icant lower than Phrynocephalus przewalskii before hibernation,and the result was opposite after hibernation.Compared with pre-hibernation,there were no difference of supercooling ability of same species,but after hibernation,the abilty to resist incolutive freezing of Phrynocephalus erythrurus has signif icantly improved,the abilty to resist incolutive freezing of Phrynocephalus przewal skii has significantly decreased.After hibernation,Phrynocephalus erythrurus has a better adaptive ability at 4?C and 0?C than Phrynocephalus przewalskii.There were no regular difference of four organic osmolytes that may acted as cryoprotectants of same species before and after hibernation.In order to better explore hibernation for Phrynocephalus erythrurus,we put Phrynocephalus erythrurus selected before hibernation at 2~4?C for 7~8 weeks to acclimatization.The results showed that compared with pre-hibernation,the ability of supercooling and resist incolutive freezing of Phrynocephalus erythrurus has signif icantly improved;its heart rate and breathing rate at 4?C and 0?C have markedly improved;there have a series of physiological changes in adaptability(such as the concentration of hemoglobin and hematocrit has signif icantly improved);but four organic osmolytes did not show regular changes.These results suggest that low temperature acclimatization can raise the adaption ability and cold hardiness of lizards,the two species of lizards are partly freeze-tolerant and incolutive freezing is benefical for lizards survival.We speculate Phrynocephalus erythrurus may hibernate below soil freezing depth and use supercooling as the way to survive in the winter.The lizards whether use the cryoprotectant and cryoprotectant types need to be further determined.