Neutral Genetic Variation (neutral + genetic_variation)

Distribution by Scientific Domains

Selected Abstracts

Evolutionary history shapes the association between developmental instability and population-level genetic variation in three-spined sticklebacks

Abstract Developmental instability (DI) is the sensitivity of a developing trait to random noise and can be measured by degrees of directionally random asymmetry [fluctuating asymmetry (FA)]. FA has been shown to increase with loss of genetic variation and inbreeding as measures of genetic stress, but associations vary among studies. Directional selection and evolutionary change of traits have been hypothesized to increase the average levels of FA of these traits and to increase the association strength between FA and population-level genetic variation. We test these two hypotheses in three-spined stickleback (Gasterosteus aculeatus L.) populations that recently colonized the freshwater habitat. Some traits, like lateral bone plates, length of the pelvic spine, frontal gill rakers and eye size, evolved in response to selection regimes during colonization. Other traits, like distal gill rakers and number of pelvic fin rays, did not show such phenotypic shifts. Contrary to a priori predictions, average FA did not systematically increase in traits that were under presumed directional selection, and the increases observed in a few traits were likely to be attributable to other factors. However, traits under directional selection did show a weak but significantly stronger negative association between FA and selectively neutral genetic variation at the population level compared with the traits that did not show an evolutionary change during colonization. These results support our second prediction, providing evidence that selection history can shape associations between DI and population-level genetic variation at neutral markers, which potentially reflect genetic stress. We argue that this might explain at least some of the observed heterogeneities in the patterns of asymmetry. [source]

Recency, range expansion, and unsorted lineages: implications for interpreting neutral genetic variation in the sharp-tailed grouse (Tympanuchus phasianellus)

Abstract Both current and historical patterns of variation are relevant to understanding and managing ecological diversity. Recently derived species present a challenge to the reconstruction of historical patterns because neutral molecular data for these taxa are more likely to exhibit effects of recent and ongoing demographic processes. We studied geographical patterns of neutral molecular variation in a species thought to be of relatively recent origin, Tympanuchus phasianellus (sharp-tailed grouse), using mitochondrial control region sequences (CR-I), amplified fragment length polymorphisms (AFLP), and microsatellites. For historical context, we also analysed CR-I in all species of Tympanuchus. Within T. phasianellus, we found evidence for restricted gene flow between eastern and western portions of the species range, generally corresponding with the range boundary of T. p. columbianus and T. p. jamesi. The mismatch distribution and molecular clock estimates from the CR-I data suggested that all Tympanuchus underwent a range expansion prior to sorting of mitotypes among the species, and that sorting may have been delayed as a result of mutation-drift disequilibrium. This study illustrates the challenge of using genetic data to detect historical divergence in groups that are of relatively recent origin, or that have a history dominated by nonequilibrium conditions. We suggest that in such cases, morphological, ecological, and behavioural data may be particularly important adjuncts to molecular data for the recognition of historically or adaptively divergent groups. [source]

Evolution of balanced genetic polymorphism

Adam Richman
Abstract Extreme genetic polymorphism maintained by balancing selection (so called because many alleles are maintained in a balance by a mechanism of rare allele advantage) is intimately associated with the important task of self/non-self-discrimination. Widely disparate self-recognition systems of plants, animals and fungi share several general features, including the maintenance of large numbers of alleles at relatively even frequency, and persistence of this variation over very long time periods. Because the evolutionary dynamics of balanced polymorphism are very different from those of neutral genetic variation, data on balanced polymorphism have been used as a novel source for inference of the history of populations. This review highlights the unique evolutionary properties of balanced genetic polymorphism, and the use of theoretical understanding in analysis and application of empirical data for inference of population history. However, a second goal of this review is to point out where current theory is incomplete. Recent observations suggest that entirely novel selective forces may act in concert with balancing selection, and these novel forces may be extremely potent in shaping genetic variation at self-recognition loci. [source]

Hierarchical modeling of genome-wide Short Tandem Repeat (STR) markers infers native American prehistory

Cecil M. Lewis Jr.
Abstract This study examines a genome-wide dataset of 678 Short Tandem Repeat loci characterized in 444 individuals representing 29 Native American populations as well as the Tundra Netsi and Yakut populations from Siberia. Using these data, the study tests four current hypotheses regarding the hierarchical distribution of neutral genetic variation in native South American populations: (1) the western region of South America harbors more variation than the eastern region of South America, (2) Central American and western South American populations cluster exclusively, (3) populations speaking the Chibchan-Paezan and Equatorial-Tucanoan language stock emerge as a group within an otherwise South American clade, (4) Chibchan-Paezan populations in Central America emerge together at the tips of the Chibchan-Paezan cluster. This study finds that hierarchical models with the best fit place Central American populations, and populations speaking the Chibchan-Paezan language stock, at a basal position or separated from the South American group, which is more consistent with a serial founder effect into South America than that previously described. Western (Andean) South America is found to harbor similar levels of variation as eastern (Equatorial-Tucanoan and Ge-Pano-Carib) South America, which is inconsistent with an initial west coast migration into South America. Moreover, in all relevant models, the estimates of genetic diversity within geographic regions suggest a major bottleneck or founder effect occurring within the North American subcontinent, before the peopling of Central and South America. Am J Phys Anthropol 2010. © 2009 Wiley-Liss, Inc. [source]

The global pattern of gene identity variation reveals a history of long-range migrations, bottlenecks, and local mate exchange: Implications for biological race

Keith L. Hunley
Abstract Several recent studies have argued that human genetic variation conforms to a model of isolation by distance, whereas others see a predominant role for long-range migrations and bottlenecks. It is unclear whether either of these views fully describes the global pattern of human genetic variation. In this article, we use a coalescent-based simulation approach to compare the pattern of neutral genetic variation predicted by these views to the observed pattern estimated from neutral autosomal microsatellites assayed in 1,032 individuals from 53 globally-distributed populations. We find that neither view predicts every aspect of the observed pattern of variation on its own, but that a combination of the two does. Specifically, we demonstrate that the observed pattern of global gene identity variation is consistent with a history of serial population fissions, bottlenecks and long-range migrations associated with the peopling of major geographic regions, and gene flow between local populations. This history has produced a nested pattern of genetic structure that is inconsistent with the existence of independently evolving biological races. We consider the implications of our findings for methods that apportion variation into within- and between-group components and for medical genetics. Am J Phys Anthropol 2009. © 2009 Wiley-Liss, Inc. [source]

Do taxonomic divisions reflect genetic differentiation?

A comparison of morphological, Satyrinae, genetic data in Coenonympha tullia (Müller)
Historically, morphological variation has been used to classify many species (and subspecies) of Lepidoptera. However, some of this variation may be unsuitable for inferring the recent evolutionary history of populations. Genetic data provide an alternative. We examine the morphological and genetic variation within and between British subspecies of Coenonympha tullia (Müller 1764) to test the hypothesis that neutral genetic variation corresponds to morphological variation. We find that most morphological and genetic variation occurs within populations and that those populations designated as subspecies based on morphological characters are not necessarily most closely related for mitochondrial DNA or nuclear DNA (amplified fragment length polymorphisms and allozymes). Thus, the notion that wing spot variation reflects population isolation and therefore genetic differentiation does not hold. The present study highlights the need for genetic data where taxonomy may be based on environmentally plastic or locally adapted characters because such characters will not reflect the true population genetic history. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 97, 314,327. [source]