Hibernation patterns and changes of body temperature in Daurian ground squirrels(Spermophilus dauricus) during hibernation

In order to understand the patterns of body temperature changes and hibernation,we used iButtons to monitor body temperatures(Tb) in a typical hibernator,the Daurian ground squirrel(Spermophilus dauricus),before,during,and after their hibernation period.Hibernation patterns and thermoregulation characteristics were analyzed.In the laboratory,there were great individual differences in the length of the hibernation time.Three types of torpor were distinguished,deep hibernation,short hibernation,and no hibernation.Three different kinds of torpor bouts could also be distinguished during the hibernation season,deep hibernation bouts(the minimal body temperature,Tbmin20℃,the duration of the hibernation bout,BD24 h),short hibernation bouts(Tbmin20℃,BD≤24 h),and daily torpor bouts(Tbmin≥20℃,BD≤24 h).The Tbmin in deep hibernation bouts(2.54℃±0.35℃) was lower than in short hibernation bouts(10.05℃±1.97℃),but the Tbmax in daily torpor bouts(38.09℃±0.17℃) was higher than in either of the other conditions(37.31℃±0.15℃ and 37.22℃±0.31℃).These results suggest that the regulation mechanism for daily torpor may be different from the other two kinds.Tbmin in deep hibernation bouts and daily torpor bouts was significantly correlated with ambient temperature(Ta).The lowest Tb we recorded was-2.43℃.In deep hibernation bouts,most individuals were able to tolerate temperatures as low as-2℃ to 0℃.The fluctuation amplitude of Tb within 10 days before hibernation was greater than after hibernation.Most animals displayed very careful body temperature reductions before entering hibernation,which imply that the thermoregulatory mechanism is schanged to a new state before hibernation starts.