The Quantitative and Molecular Genetic Architecture of a Subdivided Species

Abstract

In an effort to elucidate the evolutionary mechanisms that determine the genetic architecture of a species, we have analyzed 17 populations of the microcrustacean Daphnia pulex for levels of genetic variation at the level of life-history characters and molecular markers in the nuclear and mitochondrial genomes. This species is highly subdivided, with approximately 30% of the variation for nuclear molecular markers and 50% of the variation for mitochondrial markers being distributed among populations. The average level of genetic subdivision for quantitative traits is essentially the same as that for nuclear markers, which superficially suggests that the life-history characters are diverging at the neutral rate. However, the existence of a strong correlation between the levels of population subdivision and broadsense heritabilities of individual traits argues against this interpretation, suggesting instead that the among-population divergence of some quantitative traits (most notably body size) is being driven by local adaptation to different environments. The fact that the mean phenotypes of the individual populations are also strongly correlated with local levels of homozygosity indicates that variation in local inbreeding plays a role in population differentiation. Rather than being a passive consequence of local founder effects, levels of homozygosity may be selected for directly for their effects on the phenotype (adaptive inbreeding depression). There is no relationship between the levels of variation within populations for molecular markers and quantitative characters, and this is explained by the fact that the average standing genetic variation for life-history characters in this species is equivalent to only 33 generations of variation generated by mutation.

Population structure and strong divergent selection shape phenotypic diversification in maize landraces

“…Comparison of F st values for molecular markers and quantitative traits Some authors have raised concerns about the effects of epistasis and dominance on the expected value of Q st (Lynch et al, 1999). In the case of epistasis, Whitlock (1999) has shown that additive-by-additive epistasis would decrease the expectation of Q st .…”

Population genetic structure in a Mediterranean pine (Pinus pinaster Ait.): a comparison of allozyme markers and quantitative traits

“…The pattern of variation of quantitative traits is likely to be driven by environmental factors such as natural selection pressures (Lynch et al, 1999;Petit et al, 2000), whereas most molecular markers are considered effectively neutral. The combination of quantitative and molecular measures of variation allows one to test empirically hypotheses relating to different modes of phenotypic evolution in subdivided populations.…”

MIPoD: A Hypothesis‐Testing Framework for Microevolutionary Inference from Patterns of Divergence

“…The neutral model provides a benchmark against which actual data on trait divergence can be compared. A number of methods of this kind have been proposed for the univariate (singletrait) case (Lande 1977;Charlesworth 1984;Turelli et al 1988;Lynch 1990;Lynch et al 1999;Estes and Arnold 2007). These approaches assess the statistical significance of departures from neutral rates of evolution.…”