Wheel-running and rest activity pattern interaction in two octodontids (Octodon degus, Octodon bridgesi)

Area of Science:

• Chronobiology
• Animal Behavior
• Mammalian Physiology

Background:

• Non-photic stimuli, such as wheel-running, significantly impact the rest-activity patterns of mammals.
• Previous studies indicated a phase preference inversion in Octodon degus activity when exposed to wheel-running.

Purpose of the Study:

• To investigate the rest-activity pattern responses to ad libitum wheel-running in two species of Octodon: O. degus (crepuscular-diurnal) and O. bridgesi (nocturnal).
• To compare the masking responses to wheel-running between nocturnal and diurnal octodontids.

Main Methods:

• Wild-captured male Octodon degus (n=9) and Octodon bridgesi (n=3) were habituated to laboratory conditions for two months.
• Rest-activity patterns were recorded using an automated acquisition system under a 12:12 light-dark schedule, with and without wheel access.
• Octodon bridgesi were also studied under constant darkness with and without wheel access.

Main Results:

• Octodon degus exhibited a crepuscular activity pattern, with enhanced dark-phase activity when wheel-running was available.
• Octodon bridgesi displayed a robust nocturnal chronotype, showing no significant phase preference change with wheel-running.
• Wheel-running exposure under constant darkness led to a lengthening of the endogenous period in Octodon bridgesi.

Conclusions:

• Octodon degus and Octodon bridgesi demonstrate distinct masking responses to wheel-running, reflecting their different chronotypes.
• Wheel-running acts as a significant non-photic stimulus influencing circadian rhythms in these rodent species.