Mesocosms

Chironomids are a useful group for investigating body size responses to warming temperature, due to their high local abundance, sensitivity to environmental change and trophic position as fundamental prey for other invertebrates, fish and birds. We collected specimens of six species of chironomids every two weeks over a two-year period (2017-2018) from mesocosm experiments using five ponds at ambient temperature and five ponds at 4℃ higher than ambient temperature. We investigated 1) wing length responses to temperature within species and between sexes using a regression analysis, 2) interspecific body size responses to test whether the body size of species influences sensitivity to warming temperature, and 3) the correlation between emergence date and wing length. We found a significantly shorter wing length with warming temperature in both sexes of Procladius crassinervis and Tanytarsus nemorosus, in males of Polypedilum sordens, but no significant relationship in the other three species studied. The average body size of a species affects the magnitude of the temperature-size responses in both sexes, with larger species shrinking disproportionately more with increasing temperature. There is a significant decline in wing length with emergence date across most species studied (excluding Polypedilum nubeculosum and P. sordens), indicating that individuals emerging later in the season tend to be smaller. The reduction in body size under the predicted global warming scenario tested here has the potential to affect trophic interactions.