Physiological And Biochemical Responses Of The Chinese Pond Turtle (Mauremus Reevesii) In Northern And Southern Populations To Heat Waves

Global warming has led to frequent extreme weather,especially frequent extreme heat waves,which makes global organisms face more severe survival challenges,and reptiles,as one of ectothermic animals are seriously affected by climate warming.At present,there are many studies on reptiles subjected to acute high temperature stress,but only few studies on the physiological and biochemical responses of reptiles to heat waves.In this study,we used the Chinese pond turtle(Mauremys reevesii)in Jiaxing,Zhejiang Province("northern population")and Haikou,Hainan Province("southern population")in China as the research objects,and measured oxidative stress,antioxidant enzyme activity,related gene expression and innate immunity to detect how heat waves affected the physiological and biochemical indicators of turtles in northern and southern populations.First of all,the habitat of wild turtles has been severely destroyed because of global warming and human activities.Although breeding farms in various regions of the country provided good protection for turtles,it also resulted in frequent genetic hybridization of local populations.In order to compare the genetic differentiation between the populations of Jiaxing and Haikou,we used the mitochondrial cytochrome b(Cyt B)gene to analyze the genetic distance of the northern and southern populations.We found that there was no significant population differentiation between the two populations.Secondly,in order to understand the response pattern of innate immunity in different turtles populations while facing heat wave stimulation,we compared the concentrations of C3,C4 and lysozyme in plasma and the immune organ indexes in liver and spleen between the two populations.We found that the concentration of C3 in plasma of the two turtle populations differed significantly,while there were no significant differences in the northern population before and after treatment.The C3 concentration of the southern population was significantly higher than the control group after recovery.It's probably because that the heat waves increased the antibacterial ability of the southern population of turtles and caused immune damage.Accordingly,the innate immunity of the southern population is more susceptible to heat waves than the northern population.Finally,in order to explore how heat waves influence the oxidative stress,antioxidant enzyme activity and gene expression of different populations of turtles,we tested malondialdehyde(MDA)content,catalase(CAT)levels,superoxide dismutase(SOD)activtity and total antioxidant capacity(T-AOC)and reduced glutathione/oxidized glutathione ratio(GSH/GSSG)of liver and muscle tissues of the turtles,and we used quantitative real-time PCR technology to detect tortoise liver,muscle and brain tissue antioxidant genes(Nrf2,CAT,Mn SOD,Cu SOD)and heat shock protein 70(HSP70)gene expression levels.The results showed that the content of MDA in liver tissue of southern turtles increased significantly,SOD activity,T-AOC and GSH/GSSG decreased significantly,and CAT activity of muscle tissue increased significantly.The CAT activity and T-AOC of the liver tissue of the northern population increased significantly,GSH/GSSG decreased significantly,T-AOC of muscle tissue increased significantly,and GSH/GSSG decreased significantly.After the heat wave treatment,the expression of Nrf2,HSP70 and Mn SOD genes in the liver,brain and muscle tissues of the southern turtles and the expression of Cu SOD and CAT genes in the brain and muscle tissues were all up-regulated to varying degrees,and they were generally higher than those in the northern populations.After the recovery treatment,the expression of some genes in the tissues of the northern and southern populations increased,which may be related to the oxidative damage caused by the heat wave.This study shows that heat wave stimulation will cause the southern population to produce more oxidation product MDA,lower antioxidant enzyme activity and higher antioxidant gene expression.In summary,there is no obvious genetic differentiation among turtles in Haikou and Jiaxing populations.After heat waves treatment,the concentration of C3 in plasma and MDA in liver tissue of southern population of turtles were significantly higher than those of northern population,and the antioxidant enzyme activity of the southern population was lower than that of the northern population,and the antioxidant enzyme gene expression was higher than that of the northern population,and the response was more intense.Therefore,turtles in southern population may be more susceptible to heat waves than northern population.