QUANTIFYING FERTILITY LOSS AT HIGH TEMPERATURE ACROSS THE ANIMAL KINGDOM

The world is warming rapidly, and heatwaves are becoming more common. Many animals- including humans, livestock, pollinators, disease vectors, and species of conservation concern- lose fertility at high temperatures. Importantly, recent work suggests that sterility-inducing temperatures are often significantly lower than lethal temperatures, and that populations cannot easily evolve to maintain fertility at high temperatures. This means that rising temperatures may cause many species to become extinct due to heat-induced sterility, long before heat-induced death. Identifying the traits or factors which make species vulnerable to thermal fertility loss now will allow us to identify key conservation targets before populations start to collapse due to mass sterility. It will also allow us to predict how climate change will impact the reproductive capacity of disease vectors and species of agricultural importance, and where in the world such changes will first occur. Unfortunately, our knowledge of the factors driving thermal fertility losses in animals is rudimentary, lagging decades behind our understanding of temperature effects on survival. For example, we do not conclusively know whether male fertility is more vulnerable than female fertility. Are terrestrial species more susceptible than aquatic species? What about tropical versus temperate species? This is despite the fact that there are now thousands of published studies that record the link between animal fertility and temperature in a lab or field setting.

We have recently collected 2,333 papers examining the link between temperature and fertility across the animal kingdom. We will use this dataset to conduct the first global meta-analysis examining how rising temperature impacts animal fertility. We will test whether thermal fertility is most impacted by species phylogeny, ecology, reproductive physiology or geography. Crucially, this will allow us to begin to predict which taxa will be most at risk from a warming world, and where and when we expect to see population declines due to fertility loss. Comparing our results to lethal temperature data will also allow us to identify species with the greatest disparity between temperatures causing death vs fertility loss; in other words, species for which rising temperatures may cause severe population declines sooner than we previously thought. This will enable researchers to identify future conservation targets, develop practical biodiversity management strategies, and work to mitigate negative impacts on the reproduction of livestock, poultry and farmed-fish species.