Antarctic winters are challenging for terrestrial invertebrates, and species that live there have specialized adaptations to conserve energy and protect against cold injury in the winter. However, rapidly occurring climate change in these regions will increase the unpredictability of winter conditions, and there is currently a dearth of knowledge on how the highly adapted invertebrates of Antarctica will respond to changes in winter temperatures.

We evaluated the response of larvae of the Antarctic midge, Belgica antarctica, to simulated winters at three ecologically relevant mean temperature scenarios: Warm (-1 °C), Normal (-3 °C) and Cold (-5 °C). Within each scenario, larvae were placed into three distinct habitat types in which they are commonly observed (decaying organic matter, living moss, and Prasiola crispa algae). Following the simulated overwintering period, a range of physiological outcomes were measured, namely survival, locomotor activity, tissue damage, energy store levels and molecular stress responses.

Survival, energy stores and locomotor activity were significantly lower following the Warm overwintering environment than at lower temperatures, but tissue damage and heat shock protein expression (a proxy for protein damage) did not significantly differ between the three temperatures. Survival was also significantly lower in larvae overwintered in Prasiola crispa algae, although the underlying mechanism is unclear. Heat shock proteins were expressed least in larvae overwintering in living moss, suggesting it is less stressful to overwinter in this substrate, perhaps due to a more defined structure affording less direct contact with ice.

Our results demonstrate that a realistic 2 °C increase in winter microhabitat temperature reduces survival and causes energy deficits that have implications for subsequent development and reproduction. While our Warm winter scenario was close to the range of observed overwintering temperatures for this species, warmer winters are expected to become more common in response to climate change. Conversely, if climate change reduces the length of winter, some of the negative consequences of winter warming may be attenuated, so it will be important to consider this factor in future studies. Nonetheless, our results indicate that winter warming could negatively impact cold-adapted insects like the Antarctic midge.