Heritable variation in thermal profiles is associated with reproductive success in the world's largest bird

Large animals inhabiting extreme thermal environments, such as deserts, are predicted to be particularly vulnerable to the increasing temperature fluctuations expected in the future. However, previous work on the evolutionary potential of thermoregulation has primarily focused on the effect of hot temperatures on the survival of small ectotherms. We know little about how large endothermic vertebrates, such as birds, will respond to changing temperatures. Here we study the ostrich (Struthio camelus ), the world's largest bird, that inhabits some of the hottest and driest regions on Earth. We show that the ability of females to reproduce during hot conditions is associated with the regulation of their head temperatures ("thermoregulatory capacity"). Furthermore, variation in thermoregulation is heritable and related to past climatic conditions: females originating from parts of Africa with more extreme temperature fluctuations were better able to thermoregulate, indicating local adaptation to different climatic conditions. Together, these results suggest that thermoregulation in this large desert bird has evolved in response to past climatic conditions, remains genetically variable, and is currently under selection through its effect on reproduction.