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Offspring sex ratio in domestic goats: Trivers-Willard out of natural selection

Author

Listed:
  • J. Polák

    (Department of Zoology, Faculty of Science, Charles University in Prague, Prague, Czech Republic
    National Institute of Mental Health, Klecany, Czech Republic)

  • V. Mareš

    (Union of Sheep and Goat Breeders, Brno, Czech Republic)

  • R. Konrád

    (Union of Sheep and Goat Breeders, Brno, Czech Republic)

  • D. Frynta

    (Department of Zoology, Faculty of Science, Charles University in Prague, Prague, Czech Republic)

Abstract

The Trivers-Willard hypothesis (TWH) predicts the ability of mothers to adaptively adjust offspring sex ratio through differential maternal investment based on their relative body condition. In the present study we have analyzed an extensive data set on the secondary sex ratio (SSR) including 59 335 goat kids born in 30 633 litters to 11 644 mothers on farms all over the Czech Republic during the years 1992-2004. We found a male-biased SSR 0.568, which significantly deviates from the predicted balanced Fisherian equilibrium 1 : 1 (P < 0.0001). A generalized estimating equation model controlled for mother's identity revealed a significant effect of maternal age and season of conception (P < 0.001). Conversely, neither paternal age, gestation length, nor litter size were found to explain the sex ratio variation. We also failed to prove any effect of variables associated with maternal condition, particularly her body weight, breed, arbitrary ranking of genetic quality, and hornedness that were available in a data subset. Thus, unlike in some other ungulate species, our findings do not support the TWH in the domestic goat despite the tendency for male-biased litters and we discuss some alternative adaptive and proximate mechanism of the mammalian SSR.

Suggested Citation

  • J. Polák & V. Mareš & R. Konrád & D. Frynta, 2015. "Offspring sex ratio in domestic goats: Trivers-Willard out of natural selection," Czech Journal of Animal Science, Czech Academy of Agricultural Sciences, vol. 60(5), pages 208-215.
    • Handle: RePEc:caa:jnlcjs:v:60:y:2015:i:5:id:8170-cjas
    DOI: 10.17221/8170-CJAS
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    References listed on IDEAS

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    1. C. Tölü & T. Savaş & A. Pala & H. Thomsen, 2007. "Effects of goat social rank on kid gender," Czech Journal of Animal Science, Czech Academy of Agricultural Sciences, vol. 52(3), pages 77-82.
    2. Marco Festa-Bianchet & David W. Coltman & Luca Turelli & Jon T. Jorgenson, 2004. "Relative allocation to horn and body growth in bighorn rams varies with resource availability," Behavioral Ecology, International Society for Behavioral Ecology, vol. 15(2), pages 305-312, March.
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