Winter warm spikes reduce cold-adapted insect longevity and reproduction

Abstract

The aquatic fly family Chironomidae contains many cold-adapted, winter-active species in the Northern Hemisphere. Cold-adapted chironomid larvae develop underwater but emerge in winter as terrestrial adults to reproduce. Climate change will likely impact these winter-active adults as winter air temperatures increase. Previous studies have found constant exposure to high temperatures reduces survivorship of adult Diamesa mendotae, a cold-adapted chironomid in Minnesota. My research sought to understand how climate change could affect D. mendotae and other cold-adapted chironomids by exposing D. mendotae to high temperatures for short intervals. Here I show short-term exposure to high temperatures decreased adult D. mendotae longevity, reduced egg laying, and increased larval hatch success, but did not noticeably alter adult behaviors. Mean longevity of adult D. mendotae ranged from 14.7-24.3 days at constant 6°C, 12.3-16.8 days after exposure to 22°C for 24h, and 10.5-17.4 days after exposure to 22°C for 48h. D. mendotae eggs were also more likely to complete embryogenesis and hatch as larvae at constant 6°C than after 22°C exposure. However, D. mendotae exhibited similar behaviors over their lifespan in constant 6°C and 22°C exposure treatment groups. Taken together, I found impacts of winter short-term high temperature spikes on D. mendotae. Disruptions in D. mendotae and cold-adapted insect populations by winter warming may have broad ramifications f0r groundwater-fed stream ecosystems. This study highlights the need for further research on cold-adapted insect survivorship after short-term temperature spikes to understand seasonal impacts of climate change beyond mean annual temperature increases.