Decomposing phenotypic skew and its effects on the predicted response to strong selection

Area of Science:

• Evolutionary Biology
• Quantitative Genetics
• Ecology

Background:

• Standard evolutionary models assume normal distributions for genetic and environmental factors influencing phenotypes.
• Phenotypic skew, a deviation from normal distribution, challenges these fundamental assumptions.
• The impact of phenotypic skew on quantitative genetics, particularly heritability, remains largely unexplored.

Purpose of the Study:

• To decompose phenotypic skew and test the assumptions of quantitative genetics.
• To investigate the drivers of phenotypic skew in juvenile blue tit body size.
• To assess the consequences of skew on estimates of heritability and selection.

Main Methods:

• Analysis of phenotypic skew in the body size of juvenile blue tits (Cyanistes caeruleus).
• Decomposition of skew to identify underlying genetic and environmental contributions.
• Estimation of heritability using parent-offspring regression in the presence of skew.

Main Results:

• Substantial phenotypic skew in juvenile blue tit body size was primarily driven by environmental factors.
• Skew had a minimal direct impact on selection response predictions in this specific case.
• Nonlinear parent-offspring regressions, induced by skew and selective disappearance, significantly biased heritability estimates.

Conclusions:

• Environmental factors can create significant phenotypic skew, challenging standard evolutionary assumptions.
• Phenotypic skew can lead to overestimation of heritability, potentially explaining discrepancies in evolutionary predictions.
• The study underscores the importance of considering non-normal distributions in quantitative genetic analyses.