Abstract
Hibernation has been selected for increasing survival in harsh climatic
environments. Seasonal variability in temperature may push the body
temperatures of hibernating animals across boundaries of alternative
states between euthermic temperature and torpor temperature, typical of
either hibernation or summer dormancy. Nowadays, wearable electronics
present a promising avenue to assess the occurrence of criticality in
physiological systems, such as body temperature fluctuating between
attractors of activity and hibernation. For this purpose, we deployed
temperature loggers on two hibernating edible dormice for an entire year
and under severe Mediterranean climate conditions. Highly stochastic
body temperatures with sudden switches over time allowed us to assess
the reliability of statistical leading indicators to anticipate tipping
points when approaching a critical transition. Hibernation dynamics
showed flickering, a phenomenon occurring when a system rapidly moves
back and forth between two alternative attractors preceding the upcoming
major shift. Flickering of body temperature increased when the system
approached bifurcations, which were also anticipated by several metric-
and model-based indicators. Gradual changes in air temperature drove
long transient behavior (since flickering began long before
bifurcations) and hysteresis. For hibernating animals, hysteresis may
increase resilience when ending hibernation earlier than the optimal
time, which may occur in regions where temperatures are sharply rising,
especially during winter. Temporal changes in early indicators of
critical transitions in hibernation dynamics may help to understand the
effects of climate on evolutionary life histories and the plasticity of
hibernating organisms to cope with shortened hibernation due to global
warming.