Megachile rotundata RNA-seq from post-diapause quiescent prepupae

The genetic component of insect response to long-term, ecologically relevant temperature stress is poorly understood. Long-term low temperature exposure can lead to physiological effects collectively known as chill injury. Periodically increasing temperatures during long-term chilling has been shown to increase survival in many insects. However, the transcripts responsible for this increase in survival have never been characterized. Here we present the first transcriptome-level analysis of increased longevity under fluctuating temperatures during chilling. Overwintering post-diapause quiescent alfalfa leafcutting bees, Megachile rotundata, were exposed to a constant temperature of 6°C or 6°C with a daily fluctuation to 20°C. RNA was collected at two different time points, before and after mortality rates began to diverge between temperature treatments. Expression analysis identified differentially regulated transcripts between pairwise comparisons of both treatments and time points. Transcripts functioning in ion homeostasis, metabolic pathways, and oxidative stress response were up-regulated in individuals exposed to periodic temperature fluctuations during chilling. These provide genetic support for the hypotheses that fluctuating temperatures protect against chill injury by reducing oxidative stress and returning ion concentrations and metabolic function to more favorable levels. Additionally, exposure to fluctuating temperatures lead to increased expression of transcripts functioning in immune response and neurogenesis, providing evidence for additional mechanisms associated with increased longevity during chilling in M. rotundata.