| Summary: | As the climate warms, Arctic bumblebee species face the loss of habitat and must deal with increased competition from southern species tracking their thermal and habitat niches north, for example Bombus terrestris. Previous studies demonstrate that bumblebees follow Bergmann’s rule, i.e., larger body sizes at higher latitudes, despite bumblebees not being considered truly ectothermic, as they can generate heat through muscular activity (i.e., beating their wings). This study seeks to confirm and understand the relationship between body size and temperature using an elevational gradient as a proxy for climate. In this study, I examined 13 plots (420-1164 m.a.s.l.) set along the 3.4 km transect up the slope of Mt. Nuolja in Abisko National Park, Sweden. For body size, I chose to use the commonly accepted proxy distance between the base of the wings (i.e., intertegular distance). For temperature, I chose the mean temperature at time of visitation. Results show that climate is a significant explanatory variable for bumblebee body size, with an overall increasing body size with increasing elevation (i.e., colder climate), although most of the variance is explained by caste, i.e., queens having a larger body size than workers. Body size also shows some correlation with day of capture, which can be explained by changes in environmental conditions (e.g., temperature, flowering plant species) during the growing season experienced by the different emerging times for the castes. Given that caste was the most useful explanatory variable for body size, future studies could look at a larger environmental gradient, for example, by sampling at multiple locations along the entire Scandes mountain range to see if the effects found are localized. Further, specific habitat and specific traits of preferred plants may also help to elucidate body-size differences between species and castes. For example, many bumblebee species’ castes emerge at a specific time of year when only certain flowering plant species in specific habitats are ...
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