Common Garden Reared Bumble Bees (Bombus Vosnesenskii) Maintain Constitutive Differences in Cellular Metabolites Linked to Cold Tolerance

Abstract

Cold tolerance of ectotherms can vary strikingly among species and populations. Variation in cold tolerance can reflect differences in genomes and transcriptomes that confer cellular-level protection from cold; however, shifts in protein function and expression can be altered by other cellular constituents as cold-exposed insects from the same population often have shifts in their metabolomes. Even without a cold challenge, insects from different populations may vary in cellular composition that could alter cold tolerance, but investigations of constitutive metabolomes across populations remain rare. To address this gap, we reared Bombus vosnesenskii queens collected from Oregon and California (USA) that differ in cold tolerance (CTmin = -6 °C and 0 °C, respectively) in common garden conditions, and measured offspring metabolomes using untargeted LC-MS/MS. Some metabolites were common across body segments (head, thorax, and abdomen) likely as constituents of hemolymph. Thoracic tissue had the most distinct differences in metabolites depending on source populations likely due to hemolymph and metabolic processes that occur within the flight muscle. As predicted, metabolites previously associated with cold tolerance, including maltitol, sorbitol, and ornithine, were more abundant in the more cold-tolerant Oregon bees. Overall, our results reveal constitutive differences in metabolomes for bumble bees reared from queens collected in different locations despite no previous cold exposure; these differences likely underly, in part, population differences in cold tolerance.

Keywords: Cryoprotectant, climate, temperature, critical thermal minima, thermal tolerance, physiology