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

Organisms inhabiting extreme thermal environments, such as desert birds,
have evolved spectacular adaptations to thermoregulate during hot and cold
conditions. However, our knowledge of selection for thermoregulation and
the potential for evolutionary responses is limited, particularly for
large organisms experiencing extreme temperature fluctuations. Here we use
thermal imaging to quantify selection and genetic variation in
thermoregulation in ostriches (Struthio camelus), the world’s largest bird
species that is experiencing increasingly volatile temperatures. We found
that females that are better at regulating their head temperatures
(‘thermoregulatory capacity’) had higher egg-laying rates under hotter
conditions. Thermoregulatory capacity was both heritable and showed
signatures of local adaptation: females originating from more
unpredictable climates were better at regulating their head temperatures
in response to temperature fluctuations. Together these results reveal
that past and present evolutionary processes have shaped genetic variation
in thermoregulatory capacity, which appears to protect critical organs,
such as the brain, from extreme temperatures during reproduction.