Transcriptomic signatures of cold adaptation and heat stress in the winter ant (Prenolepis imparis)

Climate change is a serious threat to biodiversity; it is therefore important to understand how animals will react to this stress. Ectotherms, such as ants, are especially sensitive to the climate as the environmental temperature influences myriad aspects of their biology, from optimal foraging time to developmental rate. In this study, we conducted an RNA-seq analysis to identify stress-induced genes in the winter ant (Prenolepis imparis). We quantified gene expression during heat and cold stress relative to a control temperature. From each of our conditions, we sequenced the transcriptome of three individuals. Our de novo assembly included 13,324 contigs that were annotated against the nr and SwissProt databases. We performed gene ontology and enrichment analyses to gain insight into the physiological processes involved in the stress response. We identified a total of 643 differentially expressed genes across both treatments. Of these, only seven genes were differentially expressed in the cold-stressed ants, which could indicate that the temperature we chose for trials did not induce a strong stress response, perhaps due to the cold adaptations of this species. Conversely, we found a strong response to heat: 426 upregulated genes and 210 downregulated genes. Of these, ten were expressed at a greater than ten-fold change relative to the control. The transcripts we could identify included those encoding for protein folding genes, heat shock proteins, histones, and Ca2+ ion transport. One of these transcripts, hsc70-4L was found to be under positive selection. We also characterized the functional categories of differentially expressed genes. These candidate genes may be functionally conserved and relevant for related species that will deal with rapid climate change.