Seasonal Variations And Adaptation To Low Temperature Of Body Mass And Thermogenesis Properties In Eothenomys Olitor

Ambient temperature has an important effect on physiological and morphological characteristics and energy regulation of mammals.When faced with seasonal environmental changes,different groups of animals adopt different life-history strategies to adapt to the environment to maintain survival.Among them,body mass regulation and changing metabolic rate are often regarded as an important strategy.In order to adapt to the environment of the Yunnan Plateau,Eothenomys olitor has evolved its own adaptation strategy.In order to explore the survival strategy of E.olitor,seasonal experiment and cold acclimation experiment were designed in this paper,which mainly consists of three parts:(1)Seasonal variations of thermoregulation and thermal neutral zone shift in E.olitorIn order to explore the physiological adaptation characteristics of E.olitor in Zhaotong area,body temperature,Resting metabolic rate(RMR)and Thermal conductance(C)were measured in the range of 5??30?in summer and winter,respectively.The results showed that there were seasonal differences in body temperature,RMR and C value in E.olitor.Body temperature in summer was higher than that in winter,and the average body temperature was 36.17±0.52?and35.55±0.46?,respectively.The Thermal neutral zone(TNZ)showed seasonal differences.TNZ was 20??27.5?in summer and 15??25?in winter respectively,which showed that the lower limit critical point in winter was lower than that in summer.In TNZ,RMR in summer(2.76±0.19 m L O₂/g·h)was lower than that in winter(4.78±0.22 m L O₂/g·h).In summer and winter,C value in E.olitor was stable in TNZ,and the mean values were 0.18±0.02 m L O₂/g·h·?and 0.31±0.04 m L O₂/g·h·?,respectively.The above results suggested that E.olitor adapt to the climate characteristics of Zhaotong area,which were large temperature difference between winter and summer andlow annual extreme temperature by regulating body temperature,RMR and C value.(2)Variations of body mass and thermogenic properties in E.olitor in summer and winterWe investigated seasonal variations of body mass and thermogenesis properties in E.olitor by quantifying body mass,body fat mass,food intake,RMR,NST,serum leptin levels,internal organs and digestive tract mass,biochemical indexes of liver and Brown adipose tissue(BAT),gene expression of hypothalamic Neuropeptide Y(NPY),Agouti related peptide(Ag RP),Pro-opiomelanocortin(POMC),Cocaine and amphetamine regulated transcript peptide(CART)were measured between summer and winter.The results showed that body mass did not differ between summer and winter,but body fat mass was higher in summer.Food intake,RMR and NST were higher in winter.Difference of serum leptin levels between seasons was similar to that of body fat mass.Except for lung mass,cecum mass,and large intestine mass,the mass of other organs and digestive tract increased significantly in winter.Biochemical indexes of liver and BAT were higher in winter.The expressions of NPY and Ag RP were higher in winter,while POMC and CART expressions were higher in summer.All of the above results suggested that body mass of E.olitor supported the“set point regulation model”,and it adapted to the variations of seasonal environment mainly by reducing body fat mass,increasing food intake,metabolic thermogenesis and internal organs mass in winter.(3)Variations of body mass and thermogenesis properties in E.olitor during cold acclimationThe“set point regulation model”states that there is a biological control method in mammals that actively regulates body mass toward a predetermined set body mass for each individual,which may occur by regulation of energy intake or energy expenditure.In order to investigate the effects of low temperature on body mass regulation in E.olitor,body mass,body fat mass,food intake,RMR,NST,serum leptin levels,morphology,biochemical indexes of liver and BAT and hypothalamic neuropeptide genes expression were measured during cold acclimatization.The results showed that there was no significant difference in body mass but food intake,RMR and NST increased during cold acclimatization.Cytochrome c oxidase(COX)and?-glycerophosphate oxidase(?-GPO)activities in liver and BAT were significantly enhanced during cold acclimatization,and Triiodothyronine(T₃)and Thyroxine(T₄)levels in serum were significantly higher than those in the control group.Serum leptin levels decreased after cold acclimatization.Low temperature significantly increased the expression of NPY and Ag RP,while it decreased CART and POMC expressions.All of the above results suggested that body mass in E.olitor can remain relatively stable at low temperature,which conforms to the“set point regulation model”.However,the species showed differences with sympatric species,such as Eothenomys miletus,Apodemus chevrieri and Tupaia belangeri.Moreover,E.olitor can cope with low temperature by increasing its metabolic rate and thermogenesis properties.In conclusion,the shift of TNZ in E.olitor in the process of seasonal variation,and the lower limit critical point in winter was lower than that in summer.Body temperature in winter was lower than that in summer,and C value was relatively higher in winter in E.olitor.Secondly,body mass conforms to the“set point regulation model”during seasonal variation,however,the species showed differences with sympatric species,such as E.miletus,A.chevrieri and T.belangeri.The expression of serum leptin and hypothalamic neuropeptide genes are involved in the regulation of energy balance and body mass in E.olitor.In winter or low temperature,E.olitor can regulate energy balance by enhancing metabolic rate and thermogenesis properties.These characteristics of E.olitor are unique adaptive strategies evolved to adapt to the climate characteristics of Yunnan Plateau,which were large temperature difference between winter and summer and low annual extreme temperature.