Abstract:

 Temperatures in Arctic and sub-Arctic regions are highly variable, with long, and cold winters, and short summers. Studies on thermal biology of ectotherms from these latitudes have mostly focused on how organisms cope with cold temperatures. However, temperatures in microhabitats such as south-facing slopes can occasionally reach high and potentially stressful temperatures. Such microclimatic conditions are challenging for organisms, since they need to time their development to coincide with the short summer, while coping with thermal extremes during summer and winter. In the present study, we investigate upper and lower thermal limits of adults and eggs in Nysius groenlandicus, a univoltine seed bug widely distributed in Greenland and alpine areas of Scandinavia and with preference for dry and sunny habitats. Secondly, we investigate the survival strategy of the overwintering egg stage during cold exposure. We found a clear association between the microhabitat temperatures experienced by each specific life stage and their heat and cold tolerance. Thus, adults and eggs, which are both exposed to high summer temperatures, showed a high heat tolerance. Adults which do not overwinter had very poor cold tolerance, whereas eggs produced in autumn were very cold hardy (with some survival at − 21 °C). Cold tolerance of the eggs of N. groenlandicus was based on freeze avoidance through extensive supercooling and by conserving water. These results suggest life stage-specific adaptation to heat and cold stress in Arctic and sub-Arctic insects, and highlight new research avenues addressing adaptation to higher and more variable temperatures in Arctic and sub-Arctic regions.