There is recent evidence that there is heritable variation in the environmental variance of a phenotype. This may lead to non-linear relationships between traits, for instance when there is an optimum. In this study, a quantitative genetic framework and a statistical method were developed to study such relationships. Applied to piglet birth weight and survival it was found that increasing uniformity of birth weight increases piglet survival.
Environmental variance is that portion of the phenotypic variance caused by differences in the environments to which the individuals in a population have been exposed. There is recent evidence that the environmental variance of traits is under genetic control meaning that some genotypes have higher or smaller environmental variance, which would enable selection for increased uniformity. In the recent study of Han Mulder a quantitative genetic framework was developed to study non-linear relationships between traits, caused by genetic covariance of environmental variance of one trait and the mean of the other trait, e.g. environmental variance of piglet birth weight and piglet survival. In addition, we developed a method to estimate mean-variance relationships between traits and applied it to piglet birth weight and survival. We observed a non-linear relationship and a negative correlation between piglet birth weight and survival, indicating that selection for increased uniformity of piglet birth weight would increase piglet survival at birth.