Physiological and cognitive consequences of a daily 26 h photoperiod in a primate: exploring the underlying mechanisms of the circadian resonance theory.

Clara Hozer,Fabien Pifferi

doi:10.1098/rspb.2020.1079

Abstract

The biological clock expresses circadian rhythms, whose endogenous period (tau) is close to 24 h. Daily resetting of the circadian clock to the 24 h natural photoperiod might induce marginal costs that would accumulate over time and forward affect fitness. It was proposed as the circadian resonance theory. For the first time, we aimed to evaluate these physiological and cognitive costs that would partially explain the mechanisms of the circadian resonance hypothesis. We evaluated the potential costs of imposing a 26 h photoperiodic regimen compared to the classical 24 h entrainment measuring several physiological and cognitive parameters (body temperature, energetic expenditure, oxidative stress, cognitive performances) in males of a non-human primate (Microcebus murinus), a nocturnal species whose endogenous period is about 23.5 h. We found significant higher resting body temperature and energy expenditure and lower cognitive performances when the photoperiodic cycle length was 26 h. Together these results suggest that a great deviation of external cycles from tau leads to daily greater energetic expenditure, and lower cognitive capacities. To our knowledge, this study is the first to highlight potential mechanisms of circadian resonance theory.

Highlights

Circadian rhythms provide notable benefits to the organism compared with passive oscillations in local and transient response to exogenous factors [1,2]
We aimed at investigating the metabolic costs of the circadian clock daily synchronization and its cognitive consequences
Animals submitted to light–dark cycles of 26 h, inducing a great divergence between tau and external cycles, exhibited higher resting body temperature, higher VO2, VCO2 and heat levels and lower cognitive performances

Summary

Introduction

Circadian rhythms provide notable benefits to the organism compared with passive oscillations in local and transient response to exogenous factors [1,2]. Wyse et al [15] found a negative correlation between the deviation of tau from 24 h and longevity in several strains of laboratory mice, and several species of rodents and primates; Libert et al [16] showed that mice with circadian period close to 24 h lived about 20% longer than those with shorter or longer tau. These two studies provide evidence that keeping a 24 h free-running period positively affects lifespan. We assessed cognitive performance using a learning task based on visual discrimination

Results

Discussion

Findings

29. Martino TA et al 2008 Circadian rhythm