Brain size and neuron numbers drive differences in yawn duration across mammals and birds
Massen, Jorg J.M.; Hartlieb, Margarita; Martin, Jordan S.; Leitgeb, Elisabeth B.; Hockl, Jasmin; Kocourek, Martin; Olkowicz, Seweryn; Zhang, Yicheng; Osadnik, Christin; Verkleij, Jorrit W.; Bugnyar, Thomas; Němec, Pavel; Gallup, Andrew C.
(2021) Communications Biology, volume 4, issue 1
(Article)
Abstract
Recent studies indicate that yawning evolved as a brain cooling mechanism. Given that larger brains have greater thermolytic needs and brain temperature is determined in part by heat production from neuronal activity, it was hypothesized that animals with larger brains and more neurons would yawn longer to produce comparable cooling
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effects. To test this, we performed the largest study on yawning ever conducted, analyzing 1291 yawns from 101 species (55 mammals; 46 birds). Phylogenetically controlled analyses revealed robust positive correlations between yawn duration and (1) brain mass, (2) total neuron number, and (3) cortical/pallial neuron number in both mammals and birds, which cannot be attributed solely to allometric scaling rules. These relationships were similar across clades, though mammals exhibited considerably longer yawns than birds of comparable brain and body mass. These findings provide further evidence suggesting that yawning is a thermoregulatory adaptation that has been conserved across amniote evolution.
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Keywords: Medicine (miscellaneous), Biochemistry, Genetics and Molecular Biology(all), Agricultural and Biological Sciences(all)
ISSN: 2399-3642
Publisher: Springer Nature
Note: Funding Information: We are very grateful to Christian Blum, Christiane Rössler, Katie Slocombe, Sita ter Haar, Raoul Schwing, Auguste von Bayern, Jingzhi Tan, Evy van Berlo, Alejandra Díaz-Loyo, and Oscar Juárez-Mora for providing us with videos of their yawning animals. Similarly, we thank Avifauna, Tierpark Stadt Haag, Zoo Linz, Haidlhof Research Station, Konrad Lorenz Forschungsstelle Grünau and Wildtierpark Cumberland, Nationalpark Thayatal, Zoo Bratislava, Eulen-und Greifvogelstation Haringsee, Papageienschutzhaus and Tierschutzheim Vösendorf, and Tiergarten Schönbrunn and in particular Jonas Küh-napfel, for allowing us to collect videos of yawns of the animals in their collection. Part of this research was funded by the Austrian Science Fund (FWF, P 26806 to J.J.M.M.), the Czech Science Foundation (18-15020S, to P.N.), and the Grant Agency of Charles University (1438217 to M.K.). Publisher Copyright: © 2021, The Author(s).
(Peer reviewed)