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Sex ratio variation in Iberian pigs
M A Toro1, A Fernández, L A García-Cortés
1Departamento de Mejora Genética Animal, INIA, 28040 Madrid, Spain. toro@inia.es
Genetics
|April 4, 2006
Summary
Fisher's theory on sex allocation suggests natural selection favors a 1:1 sex ratio. However, this study found little evidence for heritability of sex ratio in pigs, indicating limited potential for artificial selection to modify it.
Area of Science:
- Evolutionary biology
- Quantitative genetics
- Animal breeding
Background:
- The sex ratio problem in evolutionary biology questions the adaptive significance of offspring sex ratios.
- Fisher's theory posits natural selection favors a 1:1 sex ratio, but empirical evidence and chromosomal mechanisms complicate this.
- Genetic variance for sex ratio is a key assumption in understanding parental control over offspring sex.
Purpose of the Study:
- To investigate the heritability of offspring sex ratio in pigs.
- To assess the potential for artificial selection to modify sex ratios in domestic animals.
- To evaluate the influence of maternal factors on sex ratio determination.
Main Methods:
- Analysis of a large dataset (56,807 piglets) from 550 boars and 1893 dams.
- Application of linear and threshold animal models within a Bayesian framework using Gibbs sampling.
- Statistical analysis of heterogeneity and maternal age effects on sex ratio.
Main Results:
- Heritability estimates for sex ratio were very low (0.000263 and 0.000917) under sire models.
- High probability (0.996) that heritability for sex ratio is zero under the threshold model.
- No significant trend in sex ratio was observed in relation to maternal age.
Conclusions:
- The sex ratio in pigs exhibits negligible heritability, limiting the effectiveness of artificial selection for its modification.
- Chromosomal sex determination in vertebrates acts as a constraint, precluding significant parental control over offspring sex ratios.
- Findings suggest that evolutionary and practical considerations of sex allocation must account for these biological constraints.
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