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  • Matters Arising
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Shrinking body size may not provide meaningful thermoregulatory benefits in a warmer world

Nature Ecology & Evolution volume 8, pages 387–389 (2024)Cite this article

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Matters Arising to this article was published on 15 January 2024

The Original Article was published on 27 October 2022

arising from C. Youngflesh et al. Nature Ecology and Evolution https://doi.org/10.1038/s41559-022-01893-x (2022)

In a recent and impressive analysis of avian morphological data (covering >250,000 male birds from 105 species), Youngflesh et al.1 report that birds breeding in North America have become significantly lighter over the past three decades, coincident with rising breeding season temperatures. Because these observations recapitulate predictions under Bergmann’s rule (that is, that the body size of congeners and conspecifics is usually larger near the cooler poles than near the warmer Equator), the authors argue a thermoregulatory benefit to their occurrence under the assumption that smaller-bodied animals have lower cooling costs than largerbodied animals in a warming world. We agree that warmer environments during reproduction may well explain avian body size declines. However, we question whether (1) changes in heat balance attributed to these declines are sufficiently large to explain observed size reductions, and (2) increased thermoregulatory efficiency during the short windows where reproduction occurs is always relevant, particularly when tenancy in breeding-ground temperatures is short (that is, among migrants). Generalizability of these results may be limited further by sex-specific enquiry, which overlooks the possibility of divergent selection on body size in males and females under climate warming. In this commentary, we expand on these concerns hoping to instigate discussion on knowledge gaps that need closing if we wish to better understand the proximate and ultimate drivers of shapeshifting animals in a changing world.

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Fig. 1: For most bird species, temporal changes in body masses are too small to contribute biologically meaningful shifts in heat production and dissipation, suggesting thermoregulatory benefit is an unlikely outcome of shapeshift under climate warming.

References

  1. Youngflesh, C., Saracco, J. F., Siegel, R. B. & Tingley, M. W. Abiotic conditions shape spatial and temporal morphological variation in North American birds.Nat. Ecol. Evol. 6, 1860–1870 (2022).

    Article  PubMed  Google Scholar 

  2. Ryding, S., Klaassen, M., Tattersall, G. J., Gardner, J. L. & Symonds, M. R. E. Shape-shifting: changing animal morphologies as a response to climatic warming. Trends Ecol. Evol. 36, 1036–1048 (2021).

    Article  PubMed  Google Scholar 

  3. Zimova, M. et al. Body size predicts the rate of contemporary morphological change in birds. Proc. Natl Acad. Sci. USA 120, e2206971120 (2023).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  4. Weeks, B. C. et al. Shared morphological consequences of global warming in North American migratory birds. Ecol. Lett. 23, 316–325 (2020).

    Article  PubMed  Google Scholar 

  5. Kronfeld-Schor, N. Conservation physiology. Temperature 1, 94–95 (2014).

    Article  Google Scholar 

  6. Stillman, J. H. Heat waves, the new normal: summertime temperature extremes will impact animals, ecosystems, and human communities. Physiology 34, 86–100 (2019).

    Article  CAS  PubMed  Google Scholar 

  7. McKechnie, A. E., Gerson, A. R. & Wolf, B. O. Thermoregulation in desert birds: scaling and phylogenetic variation in heat tolerance and evaporative cooling. J. Exp. Biol. 224, jeb229211 (2021).

    Article  PubMed  Google Scholar 

  8. Billerman, S. M., Keeney, B. K., Rodewald, P. G. & Schulenberg, T. S. Birds of the World (Cornell Lab of Ornithology; 2022); https://birdsoftheworld.org/bow/home

  9. Somveille, M., Manica, A. & Rodrigues, A. S. L. Where the wild birds go: explaining the differences in migratory destinations across terrestrial bird species. Ecography 42, 225–236 (2019).

    Article  ADS  Google Scholar 

  10. Weeks, B. C. et al. Temperature, size and developmental plasticity in birds. Biol. Lett. 18, 20220357 (2022).

    Article  PubMed  PubMed Central  Google Scholar 

  11. Tabh, J. K. R. & Nord, A. Temperature-dependent developmental plasticity and its effects on Allen’s and Bergmann’s rules in endotherms. Integr. Comp. Biol. 63, 758–771 (2023).

    Article  PubMed  PubMed Central  Google Scholar 

  12. Meijer, T., Möhring, F. J. & Trillmich, F. Annual and daily variation in body mass and fat of starlings Sturnus vulgaris. J. Avian Biol. 25, 98–104 (1994).

    Article  Google Scholar 

  13. Ronget, V. et al. Causes and consequences of variation in offspring body mass: meta-analyses in birds and mammals. Biol. Rev. 93, 1–27 (2018).

    Article  PubMed  Google Scholar 

  14. Perrins, C. M. Eggs, egg formation and the timing of breeding. Ibis 138, 2–15 (1996).

    Article  Google Scholar 

  15. Ballinger, M. A. & Nachman, M. W. The contribution of genetic and environmental effects to Bergmann’s rule and Allen’s rule in house mice. Am. Nat. 199, 691–704 (2022).

    Article  PubMed  Google Scholar 

  16. Schou, M. F. et al. Extreme temperatures compromise male and female fertility in a large desert bird. Nat.Commun. 12, 666 (2021).

    Article  ADS  CAS  PubMed  PubMed Central  Google Scholar 

  17. Teplitsky, C., Mills, J. A., Alho, J. S., Yarrall, J. W. & Merilä, J. Bergmann’s rule and climate change revisited: disentangling environmental and genetic responses in a wild bird population. Proc. Natl Acad. Sci. USA 105, 13492–13496 (2008).

    Article  ADS  CAS  PubMed  PubMed Central  Google Scholar 

  18. Bosco, L. et al. Increasing winter temperatures explain body size decrease in wintering bird populations of Northern Europe – but response patterns vary along the spatioclimatic gradient. Glob. Ecol. Biogeo. 32, 2100–2110 (2023).

    Article  Google Scholar 

  19. Siepielski, A. M. et al. No evidence that warmer temperatures are associated with selection for smaller body sizes. Proc. R. Soc. Lond. B 286, 20191332 (2019).

    Google Scholar 

  20. Walsberg, G. E. The relationship of the external surface area of birds to skin surface area and body mass. J. Exp. Biol. 76, 185–189 (1978).

    Article  Google Scholar 

  21. Heymsfield, S. B. et al. Chemical determination of human body density in vivo: relevance to hydrodensitometry. Am. J. Clin. Nutr. 50, 1282–1289 (1989).

    Article  CAS  PubMed  Google Scholar 

  22. Porter, W. P. & Kearney, M. Size, shape, and the thermal niche of endotherms. Proc. Natl Acad. Sci. USA 106, 19666–19672 (2009).

    Article  ADS  CAS  PubMed  PubMed Central  Google Scholar 

  23. Prinzinger, R., Pressmar, A. & Schleucher, E. Body temperature in birds. Comp. Biochem. Physiol. A 99, 499–506 (1991).

    Article  Google Scholar 

  24. Aschoff, J. Thermal conductance in mammals and birds: its dependence on body size and circadian phase. Comp. Biochem. Physiol. A 69, 611–619 (1981).

    Article  Google Scholar 

  25. McKechnie, A. E. & Wolf, B. O. The allometry of avian basal metabolic rate: good predictions need good data. Physiol. Biochem. Zool. 77, 502–521 (2004).

    Article  PubMed  Google Scholar 

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Acknowledgements

A.N. was supported by the Swedish Research Council (grant 2020-04686). E.P. was supported by the Crafoord foundation (grants 20211007 and 20221018) and a PhD studentship from Lund University. J.K.R.T. was supported by a postdoctoral grant from the Wenner-Gren Foundation (grant UPD2021-0038). E.T. was supported by a postdoctoral grant from the Carl Trygger Foundation (grant CTS21: 1173).

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  1. Lund University, Department of Biology, Section for Evolutionary Ecology, Lund, Sweden

    Andreas Nord, Elin Persson, Joshua K. R. Tabh & Elisa Thoral

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  1. Andreas Nord
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Contributions

This commentary resulted from a lab meeting at the Department of Biology, Lund University, Sweden. A.N., E.P., J.K.R.T. and E.T. conceptualized the paper and drafted the outline. A.N. wrote the first complete draft, which was revised in equal measure by E.P., J.K.R.T., E.T. and A.N.; J.K.R.T. and A.N. constructed the heat balance model, J.K.R.T. performed the modelling; J.K.R.T. and A.N. developed the graphic material; A.N. procured funding. Author names are listed in alphabetical order to reflect equal contributions.

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Correspondence to Andreas Nord.

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Nord, A., Persson, E., Tabh, J.K.R. et al. Shrinking body size may not provide meaningful thermoregulatory benefits in a warmer world. Nat Ecol Evol 8, 387–389 (2024). https://doi.org/10.1038/s41559-023-02307-2

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