Sex-specific sterility caused by extreme temperatures is likely to create cryptic changes to the operational sex ratio in Drosophila virilis

Climate change is increasing the frequency and severity of short-term heat shocks that threaten the persistence of natural populations. The effect of thermal stress on natural selection is a common topic of debate, but high temperatures can also influence sexual selection. Typically, males and females of a species can survive at similar extreme temperatures, but males have been shown to lose fertility at lower temperatures than females. Here, we examine how a brief exposure of pupae to high temperatures in the fruit fly Drosophila virilis affects adult fertility in both males and females. We find strong sexual dimorphism in temperature-induced sterility. This has the potential to quickly and unpredictably create populations composed of mostly sterile males and fertile females, resulting in changes to the operational sex ratio (OSR). These disruptions are likely to be cryptic and difficult to measure in the wild, especially considering that males can eventually recover fertility and that sterile males of some species can still copulate. Changes to the OSR in this way are likely to influence sexual selection by favouring females that can discriminate between fertile and sterilised males, and possibly leading to female-female conflict over a limited pool of fertile males. Further research on how cryptic disruptions to the OSR affect sexual selection dynamics is critical for understanding the impact of environmental change on biodiversity.