The ostrich鈥檚 long, flexible neck is an important means of staying cool in the heat and keeping warm in cooler weather, and it may have evolved partially as an adaptation to wildly variable climatic conditions.
Large animals are vulnerable to rapid temperature changes because their big bodies tend to hold on to heat. To investigate how they evolve thermal tolerance, Erik Svensson at Lund University, Sweden, and his colleagues looked to the world鈥檚 largest bird: the common ostrich (Struthio camelus).
From 2012 to 2017, they took nearly 5600 photos of 794 ostriches at an ostrich research farm in Klein Karoo, South Africa, with an infrared thermography camera. The researchers found that the neck was a 鈥渢hermal window鈥�, emitting excess heat in hot conditions and retaining heat in the cold, stabilising the temperature of the head and brain. African elephants鈥� ears and the bony casque on cassowaries鈥� heads have similar radiator-like qualities.
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The farm hosts three distinct populations of the birds: South African 鈥渂lack鈥� ostriches, Zimbabwean 鈥渂lue鈥� ostriches, and the Kenyan 鈥渞eds鈥�. Ostriches from populations that evolved in South Africa or Zimbabwe, regions with more climatic variability, were more efficient at shifting the temperature in their necks. On hot days, female ostriches with a greater difference between their head and neck temperatures laid more eggs in the following days compared with those with a smaller heat gap. This all suggests that the neck is a buffer for heat stress, the researchers argue.
They also suggest that, as the planet warms, ostrich necks could evolve to become even longer as an adaptation to harsher temperatures. Using pedigree data from ostriches on the farm, the researchers confirmed that the neck radiator鈥檚 efficiency is heritable.
The ostrich鈥檚 heat-dumping neck isn鈥檛 that surprising to at Rhodes University in South Africa, given that birds often use their long legs or wings to cool off. He also points out that ostriches use evaporation from their open mouth and throat to lose heat in warm conditions.
鈥淸The researchers] do not mention evaporative water loss at all. And evaporative water loss is probably one of the most important ways to lose heat,鈥� says Smit. He wonders if the excess heat in the neck is mostly warm blood being shunted to the head, where evaporative cooling happens.
at the University of Witwatersrand in South Africa praises the researchers for linking thermal plasticity to genetic relatedness between ostrich populations and to reproductive success. She would be interested in additional measurements to determine the neck radiator鈥檚 influence on core body temperature.
搁别蹿别谤别苍肠别:听BioRxiv, DOI:
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