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Sex‐specific demography and generalization of the Trivers–Willard theory

Nature volume 526, pages 249252 (08 October 2015) | Download Citation

Abstract

The Trivers–Willard theory1 proposes that the sex ratio of offspring should vary with maternal condition when it has sex‐specific influences on offspring fitness. In particular, mothers in good condition in polygynous and dimorphic species are predicted to produce an excess of sons, whereas mothers in poor condition should do the opposite. Despite the elegance of the theory, support for it has been limited2,3. Here we extend and generalize the Trivers–Willard theory to explain the disparity between predictions and observations of offspring sex ratio. In polygynous species, males typically have higher mortality rates4, different age‐specific reproductive schedules and more risk‐prone life history tactics than females; however, these differences are not currently incorporated into the Trivers–Willard theory. Using two‐sex models parameterized with data from free‐living mammal populations with contrasting levels of sex differences in demography, we demonstrate how sex differences in life history traits over the entire lifespan can lead to a wide range of sex allocation tactics, and show that correlations between maternal condition and offspring sex ratio alone are insufficient to conclude that mothers adaptively adjust offspring sex ratio.

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Acknowledgements

We thank Y. Vindenes, S. Cubaynes, S. West, R. K. Kanda, J. A. Deere, J. Barthold, M. Brouard, R. A. Pozo, and E. G. Simmonds for comments. We thank M. Festa‐Bianchet and F. Pelletier for access to Bighorn sheep data and feedback. We acknowledge the use of the University of Oxford Advanced Research Computing facility. S.S. was funded by an ERC Advanced Grant to T.C., P.N. is funded by a Swiss National Science Foundation grant (SNF 3100AO‐109816), and L.T. was funded by grants from the European Commission (Marie Curie Fellowship 254442) and the Carnegie Corporation of New York (B8749.R01).

Author information

Affiliations

  1. University of Oxford, Department of Zoology, Oxford OX1 3PS, UK

    • Susanne Schindler
    •  & Tim Coulson
  2. Laboratoire de Biométrie et Biologie Evolutive (UMR 5558), Université Claude Bernard Lyon 1, 43 boulevard du 11 novembre 1918, 69622 Villeurbanne Cedex, France

    • Jean‐Michel Gaillard
  3. Department of Computer Science, University of Surrey, Guildford GU2 7XH, UK

    • André Grüning
  4. Department of Biological Sciences, University of Calgary, Calgary, Alberta T2N 1N4, Canada

    • Peter Neuhaus
  5. School of Animal, Plant and Environmental Sciences, University of the Witwatersrand, Wits 2050, South Africa

    • Lochran W. Traill
  6. Department of Biology, Stanford University, Stanford, California 94305, USA

    • Shripad Tuljapurkar

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Contributions

S.S., J.M.G. and T.C. conceived and designed the study. S.S. developed the models and, with S.T., derived the formulas. S.S. and T.C. wrote the manuscript. S.S., A.G. and S.T. contributed to the mathematical formulation of the model. P.N. collated data on Columbian ground squirrels. L.T. parameterized data for bighorn sheep. T.C. parameterized data for squirrels. All authors edited the manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Susanne Schindler.

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https://doi.org/10.1038/nature14968

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