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Ultraviolet colour variation influences blue tit sex ratios

Nature volume 402, pages 874877 (23 December 1999) | Download Citation

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Abstract

Brilliant blue and violet structural colours are common plumage ornaments in birds, but their signalling functions are poorly understood1. This may be because birds also communicate in ultraviolet (UV-A) wavelengths (320–400 nm)2,3,4,5, invisible to humans, but a strong spectral component of many structural colours6. From a wild population of blue tits—Parus caeruleus, sexually dimorphic primarily in the ultraviolet7,8—we report experimental evidence that females skew the sex ratio of their offspring in response to the ultraviolet plumage ornamentation of their mates. Masking male ultraviolet reflectance reversed a positive correlation between reflectance and brood sex ratio observed in control pairs, demonstrating a causal effect of male ultraviolet ornamentation on offspring sex ratio. Ultraviolet reflectance also predicted male survival to the following breeding season, suggesting that it serves as a viability indicator. When taken together with ecological effects (laying date, nesting area), our experiments reveal that an unexpected amount of control exists over the primary sex ratio in birds, suggesting that chromosomal sex determination may not constrain the sex ratios of multiparous vertebrates.

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Acknowledgements

We thank A. Dubiec, K. Oddie, U. Unger and M. Liungman for assistance, and M. Andersson, A. Bennett, N. Burley, I. Cuthill, K. Lessells, J. Merilä, S. Verhulst and M. Zuk for comments. This work was supported by the Swedish Natural Sciences Research Council (B.C.S. and S.A.), and a scholarship from the Swedish Institute (J.S.).

Author information

Author notes

    • Ben C. Sheldon
    •  & Staffan Andersson

    These authors contributed equally to this work.

    • Ben C. Sheldon
    •  & Joanna Sendecka

    Present addresses: Department of Zoology, University of Oxford, Oxford OX1 3PS, UK (B.C.S.); Institute of Environmental Sciences, Krakow, Poland (J.S.).

Affiliations

  1. *Department of Animal Ecology,

    • Ben C. Sheldon
    •  & Joanna Sendecka
  2. Department of Evolutionary Biology, Evolutionary Biology Centre, Uppsala University, Norbyvägen 18d, S-752 36 Uppsala, Sweden

  3. §Department of Zoology, Göteborg University, Sweden

    • Staffan Andersson
    •  & Jonas Örnborg

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Correspondence to Ben C. Sheldon.

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https://doi.org/10.1038/47239

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