Transcriptional profiles rapidly return to normal following cold exposure in the bumble bee Bombus impatiens

Physiological responses to sudden shifts in temperature can determine an organism’s survival or capacity to maintain ecological functions. For organisms that may be exposed to sudden drops in temperature, both immediate responses to that exposure and the capacity for cold hardening may facilitate tolerance to cold. Bumble bees are well known for their abundance in cooler climates, but little is known about the temporal dynamics of cold response mechanisms following chill exposure. To better understand how bumble bees respond to acute cold exposure, we compared mRNA transcript abundances in commercially reared bumble bees (Bombus impatiens) exposed to 0°C for 75 min (inducing chill coma) and bees maintained at a constant ambient temperature (28°C). We used TagSeq to quantify gene expression levels in the thoracic tissue of individuals sampled at several time points immediately following cold exposure. Significant differences in transcriptional regulation are only detectable within 30 minutes after the treatment, with the most differential expression occurring at the 10-minute time point (371 DEGs). GO enrichment analysis identified up-regulation of genes associated with glycolysis, glycogen metabolism, and amino acid biosynthesis. Such patterns are indicative of a rapid recovery response post chill coma. Our results suggest bumble bees mount an acute differential transcriptional response during recovery from chill coma, that returns to baseline expression levels within an hour. Our work highlights the functions and pathways important for acute cold recovery and provides an estimated time frame for recovery from cold exposure in bumble bees.