Thermal performance curve of endurance running at high temperatures in deer mice

Abstract

The impacts of warming temperatures associated with climate change on performance are poorly understood in most mammals. Thermal performance curves are a valuable means of examining effects of temperature on performance traits, but they have rarely been used in endotherms. Here, we examined the thermal performance curve of endurance running capacity at high temperatures in the deer mouse (Peromyscus maniculatus). Endurance capacity was measured using an incremental speed test on a treadmill, and subcutaneous temperature in the abdominal region was measured as a proxy for body temperature (Tb). Endurance time at 20°C was repeatable but varied appreciably across individuals, and was unaffected by sex or body mass. Endurance capacity was maintained across a broad range of ambient temperatures (Ta) but was reduced above 35°C. Tb during running varied with Ta, and reductions in endurance were associated with Tb greater than 40°C when Ta was above 35°C. At the high Ta that limited endurance running capacity (but not at lower Ta), Tb tended to rise throughout running trials with increases in running speed. Metabolic and thermoregulatory measurements at rest showed that Tb, evaporative water loss, and breathing frequency increased at Ta of 36°C and above. Therefore, the upper threshold temperatures at which endurance capacity is impaired are similar to those inducing heat responses at rest in this species. These findings help discern the mechanisms by which deer mice are impacted by warming temperatures, and provide a general approach for examining thermal breadth of performance in small mammals.

Thermoregulatory trade-offs underlie the effects of warming summer temperatures on deer mice

“…Similarly, voluntary wheel running is only modestly affected by chronic exposure to constant temperatures from ∼20 to 30°C in house mice (Fregly et al, 1957;Vaanholt et al, 2007). Secondly, forced endurance capacity is maintained from ∼15 to 30°C in deer mice, and performance is not impaired until T a is increased above 35°C (Eizenga et al, 2022). It is more likely that decreases in running activity during the later stages of summer warming resulted from the prolonged decrease in night-time T b , as reductions in T b are known to reduce locomotor performance (Rojas et al, 2012).…”