Genetic Correlations: The Quantitative Genetics of Evolutionary Constraints

Interactions among traits that build a complex structure may be represented as genetic covariation and correlation. Genetic correlations may act as constraints, deflecting the evolutionary response from the direction of natural selection. We investigated the relative importance of drift, selection, and constraints in driving skull divergence in a group of related toad species. The distributional range of these species encompasses very distinct habitats with important climatic differences and the species are primarily distinguished by differences in their skulls. Some parts of the toad skull, such as the snout, may have functional relevance in reproductive ecology, detecting water cues. Thus, we hypothesized that the species skull divergence was driven by natural selection associated with climatic variation. However, given that all species present high correlations among skull traits, our second prediction was of high constraints deflecting the response to selection. We first extracted the main morphological direction that is expected to be subjected to selection by using within- and between-species covariance matrices. We then used evolutionary regressions to investigate whether divergence along this direction is explained by climatic variation between species. We also used quantitative genetics models to test for a role of random drift versus natural selection in skull divergence and to reconstruct selection gradients along species phylogeny. Climatic variables explained high proportions of between-species variation in the most selected axis. However, most evolutionary responses were not in the direction of selection, but aligned with the direction of allometric size, the dimension of highest phenotypic variance in the ancestral population. We conclude that toad species have responded to selection related to climate in their skulls, yet high evolutionary constraints dominated species divergence and may limit species responses to future climate change.

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A simplified calculation of the correlations between relatives

10.1101/2020.03.05.978361 ◽

2020 ◽

Author(s):

Reginald D. Smith

Keyword(s):

Path Analysis ◽

Quantitative Genetics ◽

Genetic Correlations ◽

Genomic Data ◽

Complex Task ◽

Outbred Population ◽

Common Task ◽

Rapid Calculation ◽

Simplified Calculation

AbstractThe correlations between relatives is one of the fundamental ideas and earliest success of quantitative genetics. Whether using genomic data to infer relationships between individuals or estimating heritability from correlations of phenotypes amongst relatives, understanding the theoretical genetic correlations is a common task. Calculating the correlations between arbitrary relatives in an outbred population, however, can be a careful and somewhat complex task for increasingly distant relatives. This paper introduces an equation based method that consolidates the results of path analysis and uses easily obtainable data from non-inbred pedigrees to allow the rapid calculation of additive or dominance correlations between relatives even in more complicated situations such as cousins sharing more than two grandparents and inbreeding.

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Plasticity in novel environments induces larger changes in genetic variance than adaptive divergence

10.1101/2021.02.08.430333 ◽

2021 ◽

Author(s):

Greg M. Walter ◽

Delia Terranova ◽

James Clark ◽

Salvatore Cozzolino ◽

Antonia Cristaudo ◽

...

Keyword(s):

Genetic Variation ◽

Phenotypic Plasticity ◽

Quantitative Genetics ◽

Leaf Morphology ◽

Genetic Variance ◽

Genetic Correlations ◽

Elevational Gradient ◽

Adaptive Divergence ◽

Genetic Constraints ◽

Novel Environments

AbstractGenetic correlations between traits are expected to constrain the rate of adaptation by concentrating genetic variation in certain phenotypic directions, which are unlikely to align with the direction of selection in novel environments. However, if genotypes vary in their response to novel environments, then plasticity could create changes in genetic variation that will determine whether genetic constraints to adaptation arise. We tested this hypothesis by mating two species of closely related, but ecologically distinct, Sicilian daisies (Senecio, Asteraceae) using a quantitative genetics breeding design. We planted seeds of both species across an elevational gradient that included the native habitat of each species and two intermediate elevations, and measured eight leaf morphology and physiology traits on established seedlings. We detected large significant changes in genetic variance across elevation and between species. Elevational changes in genetic variance within species were greater than differences between the two species. Furthermore, changes in genetic variation across elevation aligned with phenotypic plasticity. These results suggest that to understand adaptation to novel environments we need to consider how genetic variance changes in response to environmental variation, and the effect of such changes on genetic constraints to adaptation and the evolution of plasticity.

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Quantitative genetics and behavioural correlates of digit ratio in the zebra finch

Proceedings of The Royal Society B Biological Sciences ◽

10.1098/rspb.2005.3264 ◽

2005 ◽

Vol 272 (1581) ◽

pp. 2641-2649 ◽

Cited By ~ 62

Author(s):

Wolfgang Forstmeier

Keyword(s):

Zebra Finch ◽

Quantitative Genetics ◽

Mating Behaviour ◽

Genetic Correlations ◽

Relative Length ◽

Digit Ratio ◽

Laying Order ◽

Egg Deposition ◽

Offspring Sex ◽

Choice Chamber

A recent study on a captive zebra finch population suggested that variation in digit ratio (i.e. the relative length of the second to the fourth toe) might be an indicator of the action of sex steroids during embryo development, as is widely assumed for human digits. Zebra finch digit ratio was found to vary with offspring sex, laying order of eggs within a clutch, and to predict aspects of female mating behaviour. Hence, it was proposed that the measurement of digit ratio would give insights into how an individual's behaviour is shaped by its maternal environment. Studying 500 individuals of a different zebra finch population I set out to: (1) determine the proximate causes of variation in digit ratio by means of quantitative genetics and (2) to search for phenotypic and genetic correlations between digit ratio, sexual behaviour and aspects of fitness. In contrast to the earlier study, I found no sexual dimorphism in digit ratio and no effect of either laying order or experimentally altered hatching order on digit ratio. Instead, I found that variation in digit ratio was almost entirely additive genetic, with heritability estimates ranging from 71 to 84%. The rearing environment (from egg deposition to independence) explained an additional 5–6% of the variation in digit ratio, but there was no indication of any maternal effects transmitted through the egg. I found highly significant phenotypic correlations (and genetic correlations of similar size) between digit ratio and male song rate (positive correlation) as well as between digit ratio and female hopping activity in a choice chamber (negative correlation). Rather surprisingly, the strength of these correlations differed significantly between subsequent generations of the same population, illustrating how quickly such correlations can appear and disappear probably due to genotype–environment interactions.

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