Temporal regulation of temperature tolerances and gene expression in an arctic insect.

Terrestrial arthropods in the Arctic are exposed to highly variable temperatures that frequently reach cold and warm extremes. Yet, ecophysiological studies on arctic insects typically focus on the ability of species to tolerate low temperatures, whereas studies investigating species' physiological adaptations to periodically warm and variable temperatures are few. In this study, we investigate temporal changes in thermal tolerances and the transcriptome in the Greenlandic seed bug Nysius groenlandicus, collected in the field across different times and temperatures in Southern Greenland. We find that plastic changes in heat and cold tolerances occur rapidly (within hours) and at a daily scale in the field, and that these changes are correlated with diurnal temperature variation. Using RNA sequencing we provide molecular underpinnings of the rapid adjustments in thermal tolerance across ambient field temperatures and in the laboratory. We show that transcriptional responses are sensitive to daily temperature changes, and days characterized by high temperature variation induce markedly different expression patterns than thermally stable days. Further, genes associated with laboratory induced heat responses, including expression of heat shock proteins and vitellogenins, are shared across laboratory and the field, but induced at timepoints associated with lower temperatures in the field. Cold stress responses were not manifested at the transcriptomic level.