Abstract
Octodon degus is primarily a diurnal species, however, in laboratory conditions, it can switch from diurnal to nocturnal in response to wheel running availability. It has been proposed that this activity inversion obeys thermoregulatory constraints induced by vigorous physical exercise. Thus, its activity shifts to the night as the ambient temperature is lower.Here, we investigate the relationship between thermoregulation and the activity phase-inversion in response to wheel-running in this species. We measured behavioral activity and body temperature rhythms in diurnal naïve animals under 12 h light: 12 h dark cycles at four different ambient temperatures (spanning from ~26°C to 32°C), and following access to running wheels while maintained under high ambient temperature.Our results show that naïve degus do not shift their diurnal activity and body temperature rhythms to a nocturnal phase when subjected to sequential increases in ambient temperature. However, when they were provided with wheels under constant high-temperature conditions, all animals inverted their diurnal phase preference becoming nocturnal. Both, negative masking by light and entrainment to the dark phase appeared involved in the nocturnalism of these animals. Analysis of the thermoregulatory response to wheel running revealed some differences between masked and entrained nocturnal chronotypes.These data highlight the importance of the coupling between wheel running availability and ambient temperature in the nocturnalism of the degus. The results support the view that an innate “protective” pre-program mechanism (associating darkness and lower ambient temperature) may change the timing of behavioral activity in this species to reduce the potential risk of hyperthermia.
Highlights
Temporal niche selection in mammals results from the integrated actions of the central pacemaker and other internal or external cues that adaptively sculpt the overt circadian rhythms, without affecting the phase of the brain central pacemaker.Ambient Temperature and Wheel Running Availability in DegusOctodon degus is a caviomorph rodent from Central Chile, which has been described as diurnal with major episodes of activity at dawn and dusk (Fulk, 1976)
Our results show that a sequential increase in ambient temperature from 26◦C to 32◦C did not induce nocturnalism in naïve degus that never had previously wheel running experience
There was a trend for animals to increase their Tb following ramping of ambient temperature, this only reached statistical significance for mean Tb at night (p = 0.0602 and p = 0.0011, RM-ANOVA for Tb during light and dark phases, respectively, Figure 2D)
Summary
Temporal niche selection in mammals results from the integrated actions of the central pacemaker and other internal or external cues that adaptively sculpt the overt circadian rhythms, without affecting the phase of the brain central pacemaker (otherwise known as masking; Mrosovsky, 1999).Ambient Temperature and Wheel Running Availability in DegusOctodon degus is a caviomorph rodent from Central Chile, which has been described as diurnal with major episodes of activity at dawn and dusk (Fulk, 1976). It has been shown that degus select the dark phase with cooler ambient temperature to run in wheels (Vivanco et al, 2010c,d) but prefer to be active during the subjective night even when the ambient temperature did not change throughout the circadian day (Kas and Edgar, 1999). This raises the possibility that thermoregulation may be an endogenous overriding factor in determining nocturnal behavioral activity in this species
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
