Heart rate dynamics in a marsupial hibernator

Area of Science:

• Physiology
• Comparative Biology
• Mammalian Hibernation

Background:

• The eastern pygmy possum (Cercartetus nanus) exhibits both short torpor bouts and multi-day hibernation.
• Understanding heart rate (fH) control during torpor is crucial for studying mammalian hibernation.

Purpose of the Study:

• To investigate heart rate control mechanisms in a marsupial hibernator across different torpor stages.
• To compare heart rate variability in marsupial hibernators with that of placental hibernators.

Main Methods:

• Radiotelemetry was used to record electrocardiogram (ECG) and body temperature (Tb).
• Oxygen consumption and ventilation rates were measured.
• Heart rate, body temperature, and ambient temperature were monitored during euthermia and torpor.

Main Results:

• Heart rate and oxygen consumption were lowest during euthermia at 31°C.
• During torpor entry, heart rate slowed due to episodic cardiac activity.
• In deep torpor (Tb ~8°C), minimum heart rate was 8 beats/min, with QRS complex duration increasing significantly.
• Shivering bouts in deep torpor caused temporary increases in heart rate.

Conclusions:

• The eastern pygmy possum displays a dynamic heart rate range of approximately 600 beats/min (80-fold).
• Cardiac control and function in marsupial hibernators appear indistinguishable from placental hibernators, despite a significant evolutionary divergence.