THE MEASUREMENT OF SELECTION ON QUANTITATIVE TRAITS: BIASES DUE TO ENVIRONMENTAL COVARIANCES BETWEEN TRAITS AND FITNESS

TLDR

Regression methods for estimating selection from phenotypic data are common, but environmental correlations between fitness and traits can bias selection gradient estimates. This study shows that phenotypic covariance between fitness and a trait comprises a selection‑induced component and an environmental component, and that regressions on genotypic or breeding values can avoid this bias. The authors describe statistical procedures for estimating regression coefficients and testing for bias in phenotypic regressions. The environmental component of phenotypic covariance produces biased selection gradients, whereas genotypic regressions yield unbiased estimates.

Abstract

The use of regression techniques for estimating the direction and magnitude of selection from measurements on phenotypes has become widespread in field studies. A potential problem with these techniques is that environmental correlations between fitness and the traits examined may produce biased estimates of selection gradients. This report demonstrates that the phenotypic covariance between fitness and a trait, used as an estimate of the selection differential in estimating selection gradients, has two components: a component induced by selection itself and a component due to the effect of environmental factors on fitness. The second component is shown to be responsible for biases in estimates of selection gradients. The use of regressions involving genotypic and breeding values instead of phenotypic values can yield estimates of selection gradients that are not biased by environmental covariances. Statistical methods for estimating the coefficients of such regressions, and for testing for biases in regressions involving phenotypic values, are described.