Supplementary material from "Heatwaves impair female but not male fertility in a subsocial insect"

Climate change is increasing the frequency of heatwaves with detrimental effects on reproduction. Sex differences in thermal sensitivity of fertility could impact population persistence under global warming, with some predictions indicating increased vulnerability in males. Yet, few studies have measured both male and female fertility simultaneously. Here, we investigated the independent and combined effect of temperature stress on male and female reproductive success and offspring fitness in the burying beetle Nicrophorus vespilloides. Despite the expectation of increased thermal sensitivity in males, we found a significant reduction in all reproductive success traits when females, but not males, were exposed to a heatwave. We also found evidence for additive combined effects of heat stress on male and female fertility, although this had no downstream consequences for offspring fitness. In sum, our findings suggest that the effects of climate change on female fertility may have been underestimated. This could have important implications for populations under increasing environmental threat given that population growth tends to be determined by female fertility.