The quantitative genetics of a complex trait under continuous directional selection

The major frameworks for predicting evolutionary change assume that a phenotype's underlying genetic and environmental components are normally distributed. However, the predictions of these frameworks may no longer hold if distributions are skewed. Despite this, phenotypic skew has never been decomposed, meaning the fundamental assumptions of quantitative genetics remain untested. Here, we demonstrate that the substantial phenotypic skew in the body size of juvenile blue tits (Cyanistes caeruleus) is driven by environmental factors. Although skew had little impact on our predictions of selection response in this case, our results highlight the impact of skew on the estimation of inheritance and selection. Specifically, the non-linear parent-offspring regressions induced by skew, alongside selective disappearance, can strongly bias estimates of heritability. The ubiquity of skew and strong directional selection on juvenile body size implies that heritability is commonly overestimated, which may in part explain the discrepancy between predicted and observed trait evolution.

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Evolvability: A Quantitative-Genetics Perspective

Annual Review of Ecology Evolution and Systematics ◽

10.1146/annurev-ecolsys-011121-021241 ◽

2021 ◽

Vol 52 (1) ◽

pp. 153-175

Author(s):

Thomas F. Hansen ◽

Christophe Pélabon

Keyword(s):

Environmental Change ◽

Quantitative Genetics ◽

Evolutionary Biology ◽

Directional Selection ◽

Short Term ◽

Genetic Constraints ◽

Term Prediction ◽

Research Questions ◽

Short Term Prediction ◽

Rapid Environmental Change

The concept of evolvability emerged in the early 1990s and soon became fashionable as a label for different streams of research in evolutionary biology. In evolutionary quantitative genetics, evolvability is defined as the ability of a population to respond to directional selection. This differs from other fields by treating evolvability as a property of populations rather than organisms or lineages and in being focused on quantification and short-term prediction rather than on macroevolution. While the term evolvability is new to quantitative genetics, many of the associated ideas and research questions have been with the field from its inception as biometry. Recent research on evolvability is more than a relabeling of old questions, however. New operational measures of evolvability have opened possibilities for understanding adaptation to rapid environmental change, assessing genetic constraints, and linking micro- and macroevolution.

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Short-term Changes in the Variance: 2. Changes in the Environmental Variance

10.1093/oso/9780198830870.003.0017 ◽

2018 ◽

Author(s):

Bruce Walsh ◽

Michael Lynch

Keyword(s):

Quantitative Genetics ◽

Directional Selection ◽

Genetic Models ◽

Direct Selection ◽

Outbred Population ◽

Short Term ◽

Environmental Variance ◽

Additive Variance ◽

Indirect Response ◽

Existing Data

While classical quantitative genetics usually assumes that all genotypes have the same environmental variance (the assumption of homoscedasticity), in reality, genotypes can show heteroscedasticity in the environmental variance. When such variation is heritable (i.e., has an additive variance in an outbred population), then the environmental variance can change under selection. This can either be due to an indirect response (such as during directional selection on a trait), or through direct selection to increase the homogeneity of a trait (such as for increased uniformity during harvesting). This chapter reviews the existing data on the heritability of the environmental variance and examines several different genetic models for predicting its response.

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Gene-to-phenotype models and complex trait genetics

Australian Journal of Agricultural Research ◽

10.1071/ar05154 ◽

2005 ◽

Vol 56 (9) ◽

pp. 895 ◽

Cited By ~ 66

Author(s):

Mark Cooper ◽

Dean W. Podlich ◽

Oscar S. Smith

Keyword(s):

Quantitative Genetics ◽

Complex Traits ◽

Molecular Breeding ◽

Complex Trait ◽

Theoretical Framework ◽

Breeding Strategies ◽

Gene Effects ◽

Gene Environment ◽

Starting Point ◽

Context Dependent

The premise that is explored in this paper is that in some cases, in order to make progress in the design of molecular breeding strategies for complex traits, we will need a theoretical framework for quantitative genetics that is grounded in the concept of gene-networks. We seek to develop a gene-to-phenotype (G→P) modelling framework for quantitative genetics that explicitly deals with the context-dependent gene effects that are attributed to genes functioning within networks, i.e. epistasis, gene × environment interactions, and pleiotropy. The E(NK) model is discussed as a starting point for building such a theoretical framework for complex trait genetics. Applying this framework to a combination of theoretical and empirical G→P models, we find that although many of the context-dependent effects of genetic variation on phenotypic variation can reduce the rate of genetic progress from breeding, it is possible to design molecular breeding strategies for complex traits that on average will outperform phenotypic selection. However, to realise these potential advantages, empirical G→P models of the traits will need to take into consideration the context-dependent effects that are a consequence of epistasis, gene × environment interactions, and pleiotropy. Some promising G→P modelling directions are discussed.

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On the quantitative genetics of correlated characters under directional selection in age-structured populations

Philosophical Transactions of the Royal Society B Biological Sciences ◽

10.1098/rstb.1991.0010 ◽

1991 ◽

Vol 331 (1260) ◽

pp. 213-223 ◽

Cited By ~ 26

Keyword(s):

Quantitative Genetics ◽

Evolutionary Dynamics ◽

Natural Populations ◽

Directional Selection ◽

Structured Populations ◽

Short Term ◽

Age Structured ◽

Correlated Characters ◽

Selection Differentials ◽

Non Equilibrium

The evolution of correlated characters in natural populations depends on the demographic structure of these populations. This is often considerably more complicated than the structure of populations typically addressed by quantitative genetics, involving overlapping generations, age-dependent vital rates, and large fluctuations in recruitment from year to year. It is important to know more about such evolution because human exploitation of natural populations such as fishes is selective and has the potential to cause major changes in their properties. Here the theory of quantitative genetics of correlated characters under directional selection is extended to incorporate some demographic properties of non-equilibrium age structured populations. Short-term evolution is described in terms of changes in a matrix of mean breeding values of the traits at each age, and depends on the selection differentials in operation, together with the variances and covariances of breeding and phenotypic values. Because the selection differentials depend on the current mean phenotypic values which are themselves changing as each cohort grows older, the dynamics of mean phenotypic values within cohorts are also followed. Together, the changes in mean breeding and phenotypic values are sufficient to predict the short-term transient evolutionary dynamics of correlated characters in non-equilibrium age-structured populations. The predictions are compared with the dynamics observed in some randomly generated populations, and the application of the theory to evolution in commercially exploited populations of fish is discussed.

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Dissecting dynamics and differences of selective pressures in the evolution of human pigmentation

Biology Open ◽

10.1242/bio.056523 ◽

2021 ◽

Vol 10 (2) ◽

pp. bio056523

Author(s):

Xin Huang ◽

Sijia Wang ◽

Li Jin ◽

Yungang He

Keyword(s):

Natural Selection ◽

Complex Trait ◽

Directional Selection ◽

Genotype Data ◽

Population Groups ◽

Selective Pressures ◽

African Populations ◽

The World ◽

Dark Pigmentation ◽

Time Periods

ABSTRACTHuman pigmentation is a highly diverse and complex trait among populations and has drawn particular attention from both academic and non-academic investigators for thousands of years. Previous studies detected selection signals in several human pigmentation genes, but few studies have integrated contribution from multiple genes to the evolution of human pigmentation. Moreover, none has quantified selective pressures on human pigmentation over epochs and between populations. Here, we dissect dynamics and differences of selective pressures during different periods and between distinct populations with new approaches. We use genotype data of 19 genes associated with human pigmentation from 17 publicly available datasets and obtain data for 2346 individuals of six representative population groups from across the world. Our results quantify the strength of natural selection on light pigmentation not only in modern Europeans (0.0259/generation) but also in proto-Eurasians (0.00650/generation). Our results also suggest that several derived alleles associated with human dark pigmentation may be under positive directional selection in some African populations. Our study provides the first attempt to quantitatively investigate the dynamics of selective pressures during different time periods in the evolution of human pigmentation.This article has an associated First Person interview with the first author of the article.

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