Heritable variation in thermoregulation is associated with reproductive success in the world’s largest bird

Abstract

Organisms inhabiting extreme thermal environments, such as desert birds, have evolved various adaptations to thermoregulate during hot days and cold nights. However, our knowledge of selection acting on thermoregulatory traits and their evolutionary potential is limited, particularly for large organisms experiencing extreme temperature fluctuations. Here we show, using thermal imaging that the featherless neck of the ostrich (Struthio camelus) acts as a ‘thermal radiator’, protecting the head from overheating during hot conditions and conserving heat during cool conditions. We found substantial individual variation in thermal plasticity of the neck to dissipate heat away from the head that was associated with increased egg-laying rates during high ambient temperatures. Combined with low, but significant, heritability estimates of individual thermal profiles, these findings suggest that the ostrich neck functions as an adaptive thermal radiator with evolutionary potential. There were also signatures of past selection, since ostriches originating from more volatile climatic regions and females that incubate during hot daytime conditions exhibited especially high thermal plasticity. Taken together our results indicate that morphological adaptations involved in ostrich thermoregulation, such as the neck, are experiencing ongoing selection and are crucial for successfully reproducing under fluctuating climatic conditions.