Rapid adjustments in thermal tolerance and the metabolome to daily environmental changes – a field study on the Arctic seed bug Nysius groenlandicus

Laboratory investigations on terrestrial model-species, typically of temperate origin, have demonstrated that terrestrial ectotherms can cope with daily temperature variations by rapid heat or cold hardening. However, few studies have investigated this ability and its physiological basis in the field. This is even more true in the polar regions, where temporal and spatial temperature variations can be extreme, e.g. during the arctic summer. We examined adjustments in heat and cold tolerance in the Greenlandic seed bug <i>Nysius groenlandicus</i> to daily changes in microhabitat temperatures by collecting individuals for thermal assessment at different time points within and across days. Secondly, we assessed underlying metabolomic fingerprints using GC-MS metabolomics in a subset of individuals collected during days with either low or high temperature variation. We found a significant correlation between observed heat or cold tolerance and the ambient microhabitat temperatures at the time of capture, indicating that <i>N. groenlandicus </i>continuously and within short time-windows respond physiologically to thermal changes in their microhabitats. Concentrations of some metabolites varied significantly with time of collection and temperature. For instance, we detected elevated sugar levels in animals caught at the lowest daily field temperatures. Polyol concentrations were lower in individuals collected at the time points with the coldest temperatures and higher at the warmest temperatures. Additionally, changes in concentrations of metabolites associated with energetic metabolism was observed across collection times. Our findings suggest that hardening responses under natural conditions are marked and likely play a crucial role for coping with microhabitat temperature variation on a daily scale, and that metabolite levels are actively altered on a daily basis. Such results provide interesting new knowledge on the thermal biology of a common insect from the Arctic region, and contribute to our understanding of responses and robustness of arthropods to environmental changes in fragile and thermally variable ecosystems.