Body temperature patterns before, during, and after semi-natural hibernation in the European ground squirrel

Abstract

Body temperature patterns before, during, and after semi-natural hibernation in the European ground squirrel Hut, Roelof; Barnes, B.M.; Daan, S.; Heldmaier, G. Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. Abstract Ground squirrels undergo extreme body temperature¯uctuations during hibernation. The eect of low body temperatures on the mammalian circadian system is still under debate. Using implanted temperature loggers, we recorded body temperature patterns in European ground squirrels kept in an enclosure under natural conditions. Although hibernation onset was delayed, hibernation end corresponded closely to that measured in a ®eld population. Circadian body temperature¯uctuations were not detected during deep torpor, but indications of circadian timing of arousal episodes at higher temperatures were found at the beginning and end of hibernation. One male exhibited synchronised arousals to a relatively constant phase of the day throughout hibernation. All animals ®rst entered torpor in the afternoon. Daily body temperature¯uc-tuations were decreased or distorted during the ®rst days after hibernation. We hypothesise that hibernation may aect the circadian system by either decreasing the expression of the circadian oscillator, or by decreasing the amplitude of the circadian oscillator itself, possibly due to gradual, temperature dependent, internal desynchronisation. The latter mechanism may be bene®cial because it might facilitate post-hibernation re-entrainment rates.Keywords Circadian rhythmicity á Torpor á Euthermia á Arrhythmicity á Implantable temperature loggers Abbreviations DD continuous darkness á LD light-dark cycle á SCN suprachiasmatic nuclei

The Case of the Missing Mechanism: How Does Temperature Influence Seasonal Timing in Endotherms?

“…Body temperature drops dramatically during that life-cycle stage, sometimes below freezing temperatures (as low as −2.9°C in the Arctic ground squirrel [82]). Hibernation is however generally not continuous and most hibernating species show intermittent interruptions of their low-temperature torpid states by short arousal phases that are modulated both by endogenous circannual cycles and by ambient temperatures [83],[84]. Due to this temperature dependency of arousal frequency, energy expenditure during hibernation is minimized at ambient temperatures around 0°C [85].…”

Platelet Dynamics during Natural and Pharmacologically Induced Torpor and Forced Hypothermia

“…During torpor, metabolic activity is markedly reduced resulting in inactivity and a drop in body temperature, meanwhile various physiological parameters change including a steep decline in heart rate and ventilation rate [1]–[5]. Bouts of torpor are interspersed by short arousal periods, during which metabolism increases and body temperature returns to euthermia [2], [6], [7]. Key changes in physiological parameters are thought to lead to an increased resistance to ischemia/reperfusion [8], [9] allowing hibernating mammals to survive periods of torpor and arousal without signs of organ injury.…”

Molecular signatures of mammalian hibernation: comparisons with alternative phenotypes

“…Core clock genes including Per1 , Per2 , and Bmal1 stop oscillating in their expression levels during torpor in European hamsters ( Cricetus cricetus L. ), which suggests that the circadian clock is arrested during hibernation [9]. Circadian rhythms of body temperature have not been detected during hibernation in either Arctic or European ground squirrels, and arrhythmic patterns of body temperature continue for several weeks after the animals end torpor and resume constant high body temperatures in spring, provided they experience constant darkness [10,11]. However, very low amplitude cycles of body temperature persist during torpor in the golden-mantled ground squirrel ( Callospermophilus lateralis ) [5].…”