Phenotypic Plasticity and Population-level Variation in Thermal Physiology of the Bumblebee 'Bombus impatiens'

Abstract

Temperature variation affects most biological parameters from the molecular level to community structure and dynamics. Current studies on thermal biology assess how populations vary in response to environmental temperature, which can help determine how populations differentially respond to climate change. To date, temperature fluctuation effects on endothermic poikilotherms such as the common eastern bumblebee (Bombus impatiens) are unknown even though bumblebees are the most important natural pollinators in North America. A cold-acclimation experiment with B. impatiens colonies revealed individuals acclimated to 5°C or 10°C at night did not differ in resting metabolic rate, flight metabolic rate, wingbeat frequency, or morphological measurements, compared to the control group. Moreover, an infrared camera showed that all colonies maintained maximum nest temperature consistently above 36.8°C. A latitudinal sampling of flight metabolic rate and morphological measurements of B. impatiens from four locations spanning Ontario (N 45°; W 75°) to North Carolina (N 34°; W 77°) indicated no latitudinal trend in the measured variables. This study shows that bumblebees are well equipped to face a wide range of environmental temperatures, both in the short term and long term, and can use a combination of behavioural and physiological mechanisms to regulate body and nest temperatures. These results are reassuring on the direct effects of climate change on bumblebee ecology, but further studies on the indirect effect of temperature variation on North American bumblebees are required to predict future ecosystem dynamics.