After a 55-min delay in high school start times, students increased their sleep significantly and improved attendance and grades.

Successful reproduction in female mammals is precisely timed and must be able to withstand the metabolic demand of pregnancy and lactation. We show that kisspeptin-expressing neurons in the arcuate hypothalamus (Kiss1 ARH ) of female mice control the daily timing of food intake, along with the circadian regulation of locomotor activity, sleep, and core body temperature. Toxin-induced silencing of Kiss1 ARH neurons shifts wakefulness and food consumption to the light phase and induces weight gain. Toxin-silenced mice are less physically active and have attenuated temperature rhythms. Because the rhythm of the master clock in the suprachiasmatic nucleus (SCN) appears to be intact, we hypothesize that Kiss1 ARH neurons signal to neurons downstream of the master clock to modulate the output of the SCN. We conclude that, in addition to their wellestablished role in regulating fertility, Kiss1 ARH neurons are a critical component of the hypothalamic circadian oscillator network that times overt rhythms of physiology and behavior.

SUMMARYBats hibernate to cope with low ambient temperatures (T a ) and low food availability during winter. However, hibernation is frequently interrupted by arousals, when bats increase body temperature (T b ) and metabolic rate (MR) to normothermic levels. Arousals account for more than 85% of a batʼs winter energy expenditure. This has been associated with variation in T b , T a or both, leading to a single testable prediction, i.e. that torpor bout length (TBL) is negatively correlated with T a and T b . T a and T b were both found to be correlated with TBL, but correlations alone cannot establish a causal link between arousal and T b or T a . Because hydration state has also been implicated in arousals from hibernation, we hypothesized that water loss during hibernation creates the need in bats to arouse to drink. We measured TBL of bats (Pipistrellus kuhlii) at the same T a but under different conditions of humidity, and found an inverse relationship between TBL and total evaporative water loss, independent of metabolic rate, which directly supports the hypothesis that hydration state is a cue to arousal in bats.

Visual Abstract

Total evaporative water loss is the sum of respiratory water loss (RWL) and cutaneous water loss (CWL) and constitutes the main avenue of water loss in bats. Because bats fly and have large surface-to-volume ratios, they potentially have high rates of RWL and CWL. Most species of small insectivorous bats have the ability to reduce their body temperature (T(b)) at rest, which substantially reduces energy expenditure and water loss. We hypothesized that bats reduce evaporative water loss during bouts of deep hypothermia (torpor) by decreasing RWL and CWL. We measured T(b), RWL, CWL, and resting metabolic rate (RMR) in Kuhl's pipistrelle Pipistrellus kuhlii, a small insectivorous bat. In support of our hypothesis, we found that RWL decreased with decreasing RMR. We found that CWL was lower in torpid individuals than in normothermic bats; however, bats in deep torpor had similar or higher CWL than bats in shallow torpor, suggesting that they exert a less effective physiological control over CWL when in deep torpor. Because insectivorous bats spend most of their lives in torpor or hibernation, the regulation of CWL in different heterothermic states has relevant ecological and evolutionary consequences.