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.
Alley J. C., Fordham R. A., Minot E. O. (1995): Mother‐offspring interactions in feral goats—a behavioural perspective of maternal investment. New Zealand Journal of Zoology, 22, 17-23 https://doi.org/10.1080/03014223.1995.9518019
Alvarez L, Martin G.B, Galindo F, Zarco L.A (2003): Social dominance of female goats affects their response to the male effect. Applied Animal Behaviour Science, 84, 119-126 https://doi.org/10.1016/j.applanim.2003.08.003
Berube Celine H., Festa-Bianchet Marco, Jorgenson John T. (1996): Reproductive costs of sons and daughters in Rocky Mountain bighorn sheep. Behavioral Ecology, 7, 60-68 https://doi.org/10.1093/beheco/7.1.60
Cameron E. Z. (): Birth sex ratios relate to mare condition at conception in Kaimanawa horses. Behavioral Ecology, 10, 472-475 https://doi.org/10.1093/beheco/10.5.472
Cameron E. Z, Lemons P. R, Bateman P. W, Bennett N. C (2008): Experimental alteration of litter sex ratios in a mammal. Proceedings of the Royal Society B: Biological Sciences, 275, 323-327 https://doi.org/10.1098/rspb.2007.1401
Clutton-Brock T. H., Iason G. R. (1986): Sex Ratio Variation in Mammals. The Quarterly Review of Biology, 61, 339- https://doi.org/10.1086/415033
Clutton-Brock T. H., Albon S. D., Guinness F. E. (1984): Maternal dominance, breeding success and birth sex ratios in red deer. Nature, 308, 358-360 https://doi.org/10.1038/308358a0
Cote S.D., Festa-Bianchet M. (2001a): Offspring sex ratio in relation to maternal age and social rank in mountain goats (Oreamnos americanus). Behavioral Ecology and Sociobiology, 49, 260–265.
Cote S.D., Festa-Bianchet M. (2001b): Birthdate, mass and survival in mountain goat kids: effects of maternal characteristics and forage quality. Oecologia, 127, 230–238.
Darwin C. (1871): The Descent of Man, and Selection in Relation to Sex. John Murray Publishers Ltd., London, UK.
Dunbar R.I.M., Buckland D., Miller D. (1990): Mating strategies of male feral goats: a problem in optimal foraging. Animal Behaviour, 40, 653-667 https://doi.org/10.1016/S0003-3472(05)80695-5
Fantova M. (2000): Goat Breeding. Nakladatelství Brázda, Prague, Czech Republic. (in Czech)
Festa-Bianchet M. (1996): Offspring sex ratio studies of mammals: does publication depend upon the quality of the research or the direction of the results? Ecoscience, 3, 42–44.
Festa-Bianchet Marco, King Wendy J., Jorgenson Jon T., Smith Kirby G., Wishart William D. (1996): The development of sexual dimorphism: seasonal and lifetime mass changes in bighorn sheep. Canadian Journal of Zoology, 74, 330-342 https://doi.org/10.1139/z96-041
Festa-Bianchet M. (2004): Relative allocation to horn and body growth in bighorn rams varies with resource availability. Behavioral Ecology, 15, 305-312 https://doi.org/10.1093/beheco/arh014
Fisher R.A. (1930): The Genetical Theory of Natural Selection. Clarendon Press, Oxford, UK.
Foote R.H. (1977): Sex ratios in dairy cattle under various conditions. Theriogenology, 8, 349-356 https://doi.org/10.1016/0093-691X(77)90186-8
Frank S A (1990): Sex Allocation Theory for Birds and Mammals. Annual Review of Ecology and Systematics, 21, 13-55 https://doi.org/10.1146/annurev.es.21.110190.000305
Gorecki M.T. (2004): Hierarchy in a group of domestic goat (Capra hircus) females. EJPAU, 7. Available from: www.ejpau.media.pl/volume7/issue2/biology/art-02.html (accessed March 7, 2014).
Gorecki M.T., Koscinski K. (2003): Offspring sex ratio in domestic goat (Capra hircus). Archives of Animal Breeding, 46, 277–284.
Hewison A.J.Mark, Gaillard Jean-Michel (1999): Successful sons or advantaged daughters? The Trivers–Willard model and sex-biased maternal investment in ungulates. Trends in Ecology & Evolution, 14, 229-234 https://doi.org/10.1016/S0169-5347(99)01592-X
Hewison A. J. Mark, Gaillard Jean-Michel, Blanchard Pierrick, Festa-Bianchet Marco (2002): Maternal age is not a predominant determinant of progeny sex ratio variation in ungulates. Oikos, 98, 334-339 https://doi.org/10.1034/j.1600-0706.2002.980214.x
James W.H. (1995): What stabilizes the sex ratio? Annals of Human Genetics, 59, 243–249.
James William H. (1996): Evidence that Mammalian Sex Ratios at Birth are Partially Controlled by Parental Hormone Levels at The Time of Conception. Journal of Theoretical Biology, 180, 271-286 https://doi.org/10.1006/jtbi.1996.0102
McGinley Mark A. (1984): The Adaptive Value of Male-Biased Sex Ratios Among Stressed Animals. The American Naturalist, 124, 597- https://doi.org/10.1086/284299
Meikle Douglas B., Drickamer Lee C., Vessey Stephen H., Rosenthal Thomas L., Fitzgerald Kimberly S. (1993): Maternal dominance rank and secondary sex ratio in domestic swine. Animal Behaviour, 46, 79-85 https://doi.org/10.1006/anbe.1993.1163
POLÁK JAKUB, FRYNTA DANIEL (2009): Sexual size dimorphism in domestic goats, sheep, and their wild relatives. Biological Journal of the Linnean Society, 98, 872-883 https://doi.org/10.1111/j.1095-8312.2009.01294.x
Sachdeva K. K., Sengar O. P. S., Singh S. N., Lindahl I. L. (1973): Studies on goats: I. Effect of plane of nutrition on the reproductive performance of does. The Journal of Agricultural Science, 80, 375- https://doi.org/10.1017/S0021859600058019
Saltz David (2001): Progeny sex ratio variation in ungulates: maternal age meets environmental perturbation of demograpgy. Oikos, 94, 377-384 https://doi.org/10.1034/j.1600-0706.2001.940220.x
Sheldon Ben C., West Stuart A. (2004): Maternal Dominance, Maternal Condition, and Offspring Sex Ratio in Ungulate Mammals. The American Naturalist, 163, 40-54 https://doi.org/10.1086/381003
Tolu C., Savas S., Pala A., Thomsen H. (2007): Effects of goat social rank on kid gender. Czech Journal of Animal Science, 52, 77–82.
Trivers R. L., Willard D. E. (1973): Natural Selection of Parental Ability to Vary the Sex Ratio of Offspring. Science, 179, 90-92 https://doi.org/10.1126/science.179.4068.90
Williams G. C. (1979): The Question of Adaptive Sex Ratio in Outcrossed Vertebrates. Proceedings of the Royal Society B: Biological Sciences, 205, 567-580 https://doi.org/10.1098/rspb.1979.0085
Wilson K., Hardy I.C.W. (2002): Statistical analysis of sex ratios: an introduction. In: Hardy I.C.W. (ed.): Sex Ratio: Concepts and Research Methods. Cambridge University Press, Cambridge, UK, 48–92.
Zeder M. A. (): The Initial Domestication of Goats (Capra hircus) in the Zagros Mountains 10,000 Years Ago. Science, 287, 2254-2257 https://doi.org/10.1126/science.287.5461.2254