Thermal sensitivity of eggs exceeds that of sperm when exposed to experimental heatwaves in a model insect

Thermal stress from extreme weather events such as heatwaves is becoming more frequent under continued climate change, resulting inin negative impacts on biodiversity. Recent work revealed detrimental effects of thermal stress on insect sperm, which can reduce population viability. However, relatively little is known about how insect eggs are affected by thermal stress. Here, we directly compared how short-term thermal stress simulating ecologically relevant heatwaves across a range of temperatures affects sperm and eggs in a model insect, the red flour beetle (Tribolium castaneum). We show that a very brief heatwave conditions of two to five hours resulted in strong negative effects and eggs were more sensitive than sperm. These results suggest that eggs may be particularly sensitive to extreme weather conditions and suggest that further work is needed to evaluate the generality of these findings across taxa. High egg sensitivity to heatwaves is an important factor to consider when evaluating insect population responses to warming climate.