Chronic food shortage and seasonal modulations of daily torpor and locomotor activity in the grey mouse lemur (Microcebus murinus)

Abstract

The extent to which seasonal plasticity in torpor displayed by one of the smallest Malagasy primates (Microcebus murinus) will help survival in the context of ongoing global change-induced chronic food shortage, is unknown. Body temperature (Tb) and locomotor activity were measured by telemetry in short- (SD, winter-acclimated) and long-days (LD, summer-acclimated) males (n = 24) during an experimental 35-day calorie restriction of 40 or 80%. Under SD exposure, regardless of calorie restriction intensity, mouse lemurs immediately increased torpor depth and duration by 4.6-fold, and showed greater phase-advanced entry into torpor (2.4-fold). Tb adjustments were efficient under 40% calorie restriction to maintain body mass, whereas they did not prevent a 0.71 +/- 0.11 g/day mass loss during 80% calorie restriction. The 40% food-deprived LD animals combined an early shallow deepening of torpor (1 degrees C) and a late 18% decrease in locomotor activity, resulting in a moderate 6% mass loss. After 15 days of 80% calorie restriction, LD animals exhibited a SD phenotype by increasing their torpor duration and phase-advancing the entry of torpor (16 min/day). Those adjustments had no impact on mass loss (0.93 +/- 0.07 g/day) as locomotor activity increased four-fold. Daily torpor allows M. murinus to face moderate food shortage whatever the photoperiod but poorly mitigates energy imbalance during severe food deprivation, especially under LD exposure. Although the behavioral thermoregulation role warrants further investigation in energy savings, M. murinus survival would be impaired during long-term food shortage in summer.