Temperatures that sterilise males better predict global species distributions than lethal temperatures

Predicting how biodiversity will respond to increased temperatures caused by climate change is vital. However, our understanding of the traits that determine species’ response to thermal stress remains incomplete. Laboratory measurements of lethal temperatures have successfully been used to predict global species distributions and the vulnerability of species to future climate change. However, although it has long been known that fertility is sensitive to heat stress, temperatures that cause sterility have not been incorporated into predictions about how climate change will affect biodiversity. Here we show that male sterility temperatures predict the global distributions of 43 species of Drosophila substantially better than their lethal temperatures. This strongly suggests that thermal limits to reproduction can underpin how temperature affects species’ distributions. High temperatures impair male fertility across a broad range of animals and plants, so many organisms may be more vulnerable to high temperatures than currently expected.