Impacts of daily rhythms plasticity on energy budget in a South American subterranean rodent

TACHINARDI P; VALENTINUZZI VS; BUCK LC; ODA GA

Sao Paulo

Workshop; International Workshop on Organism-environment interactions: timing, plasticity and metabolic adjustments; 2018

Plasticity in circadian rhythmicity is becoming a subject of increasing interest for chronobiologists. Switches from nocturnality in the laboratory to diurnality in the field, recently reported for many rodent species, are striking examples of rhythmic plasticity. The subterranean rodent tuco-tuco (Ctenomys aff. knighti) is among the species which display such switches, being nocturnal in standard lab conditions but displaying a significant amount of activity during the light hours of the day in the field. Energetic challenges, which differ between field and lab, could trigger this difference in temporal patterns of activity. In laboratory, animals are fed ad libitum and kept at a constant ambient temperature (Ta), while in nature they expend energy with foraging and face large Ta variations. The ?circadian thermo-energetics (CTE) hypothesis? (Hut et al., 2012) proposes that daytime activity could be a response to energetic challenges by allowing the animal to maintain lower body temperature and rest in sheltered burrows during the coldest hours of the night. Studying wild animals under both captive and natural conditions can increase understanding of how temporal activity patterns are shaped by the environment and could serve as a test of the CTE hypothesis. We estimated the effects of activity timing on energy expenditure for the tuco-tuco by combining laboratory measurements of metabolic rate with environmental temperature records in both winter and summer. We showed that the implications of diurnal activity on the energy budget depends on the season. In winter, there would be considerable energy savings if activity is allocated at least partially during daylight, lending support to the CTE hypothesis. In summer, the impact of activity timing on energy expenditure is small suggesting that during this season, other factors, such as predation risk, water balance and social interaction may have more important roles than energetics in the determination of activity time.