Thermoregulatory Trade-Offs Underlie the Effects of Warming Summer Temperatures on Deer Mice

Abstract

As global temperatures continue to rise due to the effects of climate change, the ability of endotherms to property thermoregulate and maintain normal body temperature (Tb) may be challenged. The effects of warming summer temperatures on activity and thermoregulatory physiology in small mammals remain poorly understood. Using deer mice (Peromyscus maniculatus), a nocturnal species that maintains high activity in the wild allows us to investigate whether ecologically realistic summer ambient temperatures (Ta) will impact the physiology and activity of these animals. With exposure to warming temperatures up to 38°C, animals had a strong Tb dysregulation that culminated in a complete reversal of the diel pattern of Tb variation during the late weeks of the summer warming acclimation. During this, Tb surged to extreme highs (~40°C) during daytime heat but extreme lows (~34°C) at cooler nighttime temperatures. The decrease in nighttime Tb was associated with a decrease in thermogenic capacity and decreased mass and uncoupling protein (UCP1) content of brown adipose tissue. Activity, body mass and food consumption were also reduced, and water consumption was increased in later stages of summer warming. However, there was an increased capacity for heat dissipation through evaporative water loss (EWL) and a lower baseline metabolic rate typically of heat acclimation. Therefore, we propose that thermoregulatory trade-offs associated with heat acclimatization may limit nighttime activity, impacting the ability of nocturnal mammals to perform behaviours important for fitness in the wild.