Neutral Genetic Differentiation (neutral + genetic_differentiation)

Distribution by Scientific Domains

Selected Abstracts

Clonal erosion and genetic drift in cyclical parthenogens , the interplay between neutral and selective processes

Abstract The occurrence of alternating phases of clonal and sexual reproduction may strongly impact the interplay between neutral and selective genetic variation in populations. Using a physiologically structured model of the life history of Daphnia, we investigated to what extent clonal erosion associated with selection during the clonal phase affects the genetic structure as observed by neutral markers. Incorporating conservative levels of quantitative genetic variation at 11 physiological and life history traits induces strong clonal erosion, reducing clonal diversity (CD) near the end of the simulations (1000 days) to a level between 1 and 5, even in habitats with high initial CD (108 clones). This strong clonal erosion caused by selection can result in reduced genetic diversity, significant excess of heterozygotes and significant genetic differentiation between populations as observed by neutral markers. Our results indicate that, especially in relatively small habitats, clonal selection may strongly impact the genetic structure and may contribute to the often observed high level of neutral genetic differentiation among natural populations of cyclical parthenogens. [source]

Maternal genetic effects on adaptive divergence between anadromous and resident brook charr during early life history

Abstract The importance of directional selection relative to neutral evolution may be determined by comparing quantitative genetic variation in phenotype (QST) to variation at neutral molecular markers (FST). Quantitative divergence between salmonid life history types is often considerable, but ontogenetic changes in the significance of major sources of genetic variance during post-hatch development suggest that selective differentiation varies by developmental stage. In this study, we tested the hypothesis that maternal genetic differentiation between anadromous and resident brook charr (Salvelinus fontinalis Mitchill) populations for early quantitative traits (embryonic size/growth, survival, egg number and developmental time) would be greater than neutral genetic differentiation, but that the maternal genetic basis for differentiation would be higher for pre-resorption traits than post-resorption traits. Quantitative genetic divergence between anadromous (seawater migratory) and resident Laval River (Québec) brook charr based on maternal genetic variance was high (QST > 0.4) for embryonic length, yolk sac volume, embryonic growth rate and time to first response to feeding relative to neutral genetic differentiation [FST = 0.153 (0.071,0.214)], with anadromous females having positive genetic coefficients for all of the above characters. However, QST was essentially zero for all traits post-resorption of the yolk sac. Our results indicate that the observed divergence between resident and anadromous brook charr has been driven by directional selection, and may therefore be adaptive. Moreover, they provide among the first evidence that the relative importance of selective differentiation may be highly context-specific, and varies by genetic contributions to phenotype by parental sex at specific points in offspring ontogeny. This in turn suggests that interpretations of QST - FST comparisons may be improved by considering the structure of quantitative genetic architecture by age category and the sex of the parent used in estimation. [source]

Comparison of quantitative and molecular genetic variation of native vs. invasive populations of purple loosestrife (Lythrum salicaria L., Lythraceae)

Abstract Study of adaptive evolutionary changes in populations of invasive species can be advanced through the joint application of quantitative and population genetic methods. Using purple loosestrife as a model system, we investigated the relative roles of natural selection, genetic drift and gene flow in the invasive process by contrasting phenotypical and neutral genetic differentiation among native European and invasive North American populations (QST , FST analysis). Our results indicate that invasive and native populations harbour comparable levels of amplified fragment length polymorphism variation, a pattern consistent with multiple independent introductions from a diverse European gene pool. However, it was observed that the genetic variation reduced during subsequent invasion, perhaps by founder effects and genetic drift. Comparison of genetically based quantitative trait differentiation (QST) with its expectation under neutrality (FST) revealed no evidence of disruptive selection (QST > FST) or stabilizing selection (QST < FST). One exception was found for only one trait (the number of stems) showing significant sign of stabilizing selection across all populations. This suggests that there are difficulties in distinguishing the effects of nonadaptive population processes and natural selection. Multiple introductions of purple loosestrife may have created a genetic mixture from diverse source populations and increased population genetic diversity, but its link to the adaptive differentiation of invasive North American populations needs further research. [source]

Are QST,FST comparisons for natural populations meaningful?

Abstract Comparisons between putatively neutral genetic differentiation amongst populations, FST, and quantitative genetic variation, QST, are increasingly being used to test for natural selection. However, we find that approximately half of the comparisons that use only data from wild populations confound phenotypic and genetic variation. We urge the use of a clear distinction between narrow-sense QST, which can be meaningfully compared with FST, and phenotypic divergence measured between populations, PST, which is inadequate for comparisons in the wild. We also point out that an unbiased estimate of QST can be found using the so-called ,animal model' of quantitative genetics. [source]

The relative role of drift and selection in shaping the human skull

Lia Betti
Abstract Human populations across the world vary greatly in cranial morphology. It is highly debated to what extent this variability has accumulated through neutral processes (genetic drift) or through natural selection driven by climate. By taking advantage of recent work showing that geographic distance along landmasses is an excellent proxy for neutral genetic differentiation, we quantify the relative role of drift versus selection in an exceptionally large dataset of human skulls. We show that neutral processes have been much more important than climate in shaping the human cranium. We further demonstrate that a large proportion of the signal for natural selection comes from populations from extremely cold regions. More generally, we show that, if drift is not explicitly accounted for, the effect of natural selection can be greatly overestimated. Am J Phys Anthropol, 2010. © 2009 Wiley-Liss, Inc. [source]