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23 results for “maintenance of variation”
Data from: Dominance reversals and the maintenance of genetic variation
<p>Beneficial reversals of dominance reduce the costs of genetic trade-offs and can enable selection to maintain genetic variation for fitness. Beneficial dominance reversals are characterized by the beneficial allele for a given context (<em>e.g.</em> habitat, developmental stage, trait, or sex) being dominant in that context but recessive where deleterious. This context-dependence at least partially mitigates the fitness consequence of heterozygotes carrying one non-beneficial allele for their context and can result in balancing selection that maintains alternative alleles. Dominance reversals are theoretically plausible and are supported by mounting empirical evidence. Here we highlight the importance of beneficial dominance reversals as a mechanism for the mitigation of genetic conflict and review the theory and empirical evidence for them. We identify some areas in need of further research and development and outline three methods (dominance ordination, allele-specific expression, and allele-specific ATAC-Seq) that could facilitate the identification of antagonistic genetic variation. There is ample scope for the development of new empirical methods as well as reanalysis of existing data through the lens of dominance reversals. A greater focus on this topic will expand our understanding of the mechanisms that resolve genetic conflict and whether they maintain genetic variation.</p>
Data from: Dominance reversals and the maintenance of genetic variation
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Data for: Feedback between coevolution and epidemiology can help or hinder the maintenance of genetic variation in host-parasite models
<p>Antagonistic coevolution has long been suggested to help maintain host genetic variation. While, ecological and epidemiological feedbacks are known to have important consequences on coevolutionary allele frequency dynamics, their effects on the maintenance of genetic variation remains poorly understood.Here, we extend our previous work on the maintenance of genetic variation in a classic matching-alleles coevolutionary model by exploring the effects of ecological and epidemiological feedbacks, where both allele frequencies and population sizes are allowed to vary over time. We find that coevolution rarely maintains more host genetic variation than expected under neutral genetic drift alone. When and if coevolution maintains or depletes genetic variation relative to neutral drift is determined, predominantly, by two factors: the deterministic stability of the Red Queen allele frequency cycles and the chance of allele fixation in the pathogen, as this results in directional selection and depletion of genetic variation in the host. Compared to purely coevolutionary models with constant host and pathogen population sizes, ecological and epidemiological feedbacks stabilize Red Queen cycles deterministically, but population fluctuations in the pathogen increase the rate of allele fixation in the pathogen, especially in epidemiological models. Our results illustrate the importance of considering the ecological and epidemiological context in which coevolution occurs when examining the impact of Red Queen cycles on genetic variation.</p>
Data from: Maintenance and expansion of genetic and trait variation following domestication in a clonal crop: Enset tGBS individual genotype data
<p class="MsoNormal">Clonal propagation enables favourable crop genotypes to be rapidly selected and multiplied. However, the absence of sexual propagation can lead to low genetic diversity and accumulation of deleterious mutations, which may eventually render crops less resilient to pathogens or environmental change. To better understand this trade-off, we characterise the domestication and contemporary genetic diversity of Enset (<em>Ensete ventricosum</em>), an indigenous African relative of bananas (<em>Musa</em>) and principal starch staple for 20 million Ethiopians. Wild enset is strictly sexually outcrossing, but in cultivation is propagated clonally and associated with diversification and specialisation into hundreds of named landraces. We applied tGBS sequencing to generate genome-wide genotypes for 192 accessions from across enset's cultivated distribution, and surveyed 1340 farmers on enset agronomic traits. Overall, reduced heterozygosity in the domesticated lineage was consistent with a domestication bottleneck that retained 37% of wild diversity. However, an excess of putatively deleterious missense mutations at low frequency present as heterozygotes suggested accumulation of mutational load in clonal domesticated lineages. Our evidence indicates that the major domesticated lineages initially arose through historic sexual recombination associated with a domestication bottleneck, followed by amplification of favourable genotypes through an extended period of clonal propagation. Among domesticated lineages we found significant phylogenetic signal for multiple farmer-identified food, nutrition and disease resistance traits and little evidence of contemporary recombination. Development of future-climate adapted genotypes may require crop breeding, but outcrossing risks exposing deleterious alleles as homozygotes. This trade-off may partly explain the ubiquity and persistence of clonal propagation over recent centuries of comparative climate stability.</p>
Variation in Natremia Using Two Different Maintenance Intravenous Fluids in Postsurgical Hospitalized Children
ClinicalTrials.gov study NCT01251770. IPD Sharing: Not stated. Countries: 1. Publications: 3.
Data from: Maintenance and expansion of genetic and trait variation following domestication in a clonal crop: Enset tGBS individual genotype data
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Genotype-environment interaction and the maintenance of genetic variation: an empirical study of Lobelia inflata (Campanulaceae)
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Data for: Feedback between coevolution and epidemiology can help or hinder the maintenance of genetic variation in host-parasite models
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Data from: Diverse reproductive barriers in hybridising crickets suggests extensive variation in the evolution and maintenance of isolation
Reproductive barriers reduce gene flow between populations and maintain species identities. A diversity of barriers exist, acting before, during and after mating. To understand speciation and coexistence, these barriers need to be quantified and their potential interactions revealed. We use the hybridising field crickets Gryllus bimaculatus and G. campestris as a model to understand the full compliment and relative strength of reproductive barriers. We find that males of both species prefer conspecific females, but the effect is probably too weak to represent a barrier. In contrast, prezygotic barriers caused by females being more attracted to conspecific male song and preferentially mounting and mating with conspecifics are strong and asymmetric. Postzygotic barriers vary in direction; reductions in fecundity and egg viability create selection against hybridisation, but hybrids live longer than pure-bred individuals. Hybrid females show a strong preference for G. bimaculatus songs, which together with a complete lack of hybridisation by G. campestris females, suggests that asymmetric gene flow is likely. For comparison, we review reproductive barriers that have been identified between other Gryllids and conclude that multiple barriers are common. Different species pairs are separated by qualitatively different combinations of barriers, suggesting that reproductive isolation and even the process of speciation itself may vary widely even within closely related groups.
Data from: Testing for beneficial reversal of dominance during salinity shifts in the invasive copepod Eurytemora affinis, and implications for the maintenance of genetic variation
Maintenance of genetic variation at loci under selection has profound implications for adaptation under environmental change. In temporally and spatially varying habitats, non-neutral polymorphism could be maintained by heterozygote advantage across environments (marginal overdominance), which could be greatly increased by beneficial reversal of dominance across conditions. We tested for reversal of dominance and marginal overdominance in salinity tolerance in the salt-to-freshwater invading copepod Eurytemora affinis. We compared survival of F1 offspring generated by crossing saline and freshwater inbred lines (between-salinity F1 crosses) relative to within-salinity F1 crosses, across three salinities. We found evidence for both beneficial reversal of dominance and marginal overdominance in salinity tolerance. In support of reversal of dominance, survival of between-salinity F1 crosses was not different from that of freshwater F1 crosses under freshwater conditions and saltwater F1 crosses under saltwater conditions. In support of marginal overdominance, between-salinity F1 crosses exhibited significantly higher survival across salinities relative to both freshwater and saltwater F1 crosses. Our study provides a rare empirical example of complete beneficial reversal of dominance associated with environmental change. This mechanism might be crucial for maintaining genetic variation in salinity tolerance in E. affinis populations, allowing rapid adaptation to salinity changes during habitat invasions.
Data from: Testing for beneficial reversal of dominance during salinity shifts in the invasive copepod Eurytemora affinis, and implications for the maintenance of genetic variation
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Data from: Environmental stress and resource availability affect the maintenance of genetic variation in a dominant marsh plant (Spartina alterniflora)
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Data from: Diverse reproductive barriers in hybridising crickets suggests extensive variation in the evolution and maintenance of isolation
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Maintenance of variation in virulence and reproduction in populations of an agricultural plant pathogen
<p>Genetic diversity within pathogen populations is critically important for predicting pathogen evolution, disease outcomes, and prevalence. However, we lack a good understanding of the processes maintaining genetic variation and constraints on pathogen life‐history evolution. Here, we analyzed interactions between 12 wheat host genotypes and 145 strains of <i>Zymoseptoria tritici</i> from five global populations to investigate the evolution and maintenance of variation in pathogen virulence and reproduction. We found a strong positive correlation between virulence (amount of leaf necrosis) and reproduction (pycnidia density within lesions), with substantial variation in both traits maintained within populations. On average, highly virulent isolates exhibited higher reproduction, which might increase transmission potential in agricultural fields planted to homogeneous hosts at a high density. We further showed that pathogen strains with a narrow host range (i.e. specialists) for reproduction were on average less virulent, and those with a broader host range (i.e. generalists) were on average less fecund on a given specific host. These costs associated with adaptation to different host genotypes might constrain the emergence of generalists by disrupting the directional evolution of virulence and fecundity. We conclude that selection favoring pathogen strains that are virulent across diverse hosts, coupled with selection that maximizes fecundity on specific hosts, may explain the maintenance of these pathogenicity traits within and among populations.</p>
Multilevel selection on offspring size and the maintenance of variation
<p>Multilevel selection on offspring size occurs when offspring fitness depends on both absolute size (hard selection), and size relative to neighbours (soft selection). We examined multilevel selection on egg size at two biological scales: within clutches and among females, for an external fertilising tubeworm. We exposed clutches of eggs to two sperm environments (limiting and saturating) and measured their fertilisation success. We then modelled environmental (sperm) differences in hard and soft selection on individual eggs, as well as selection on clutch-level traits (means and variances). Hard and soft selection differed in strength and form depending on sperm availability – hard selection was consistently stabilising; soft selection was directional and favoured eggs relatively larger (sperm limitation) or smaller (sperm saturation) than the clutch-mean. At the clutch-level, selection on mean-egg size was largely stabilising; whilst selection on within-clutch variance was weak, but generally negative – although some correlational selection occurred between these two traits. Importantly, we found that the optimal clutch-mean egg size differed for mothers and offspring, suggesting some antagonism between the levels of selection. We thus identify several pathways that may maintain offspring-size variation: environmentally (sperm)-dependent soft selection; antagonistic multilevel selection; and correlational selection on clutch-means and variances. Multilevel approaches are powerful, but seldom used, tools for studies of offspring size and we encourage their future use.</p>
Data from: Antagonistic pleiotropy in species with separate sexes, and the maintenance of genetic variation in life-history traits and fitness
Antagonistic pleiotropy (AP) – where alleles of a gene increase some components of fitness at a cost to others – can generate balancing selection, and contribute to the maintenance of genetic variation in fitness traits, such as survival, fecundity, fertility, and mate competition. Previous theory suggests that AP is unlikely to maintain variation unless antagonistic selection is strong, or AP alleles exhibit pronounced differences in genetic dominance between the affected traits. We show that conditions for balancing selection under AP expand under the likely scenario that the strength of selection on each fitness component differs between the sexes. Our model also predicts that the vast majority of balanced polymorphisms have sexually antagonistic effects on total fitness, despite the absence of sexual antagonism for individual fitness components. We conclude that AP polymorphisms are less difficult to maintain than predicted by prior theory, even under our conservative assumption that selection on components of fitness is universally sexually concordant. We discuss implications for the maintenance of genetic variation, and for inferences of sexual antagonism that are based on sex-specific phenotypic selection estimates – many of which are based on single fitness components.
Data from: Genotyping-in-Thousands by sequencing of archival fish scales reveals maintenance of genetic variation following a severe demographic contraction in kokanee salmon
<p>Historical DNA analysis of archival samples has added new dimensions to population genetic studies, enabling spatiotemporal approaches for reconstructing population histories and informing conservation management. Here we tested the efficacy of Genotyping-in-Thousands by sequencing (GT-seq) for collecting targeted single nucleotide polymorphism (SNP) genotypic data from archival scale samples, and demonstrate its application to a study of kokanee salmon (<i>Oncorhynchus nerka</i>) in Kluane National Park and Reserve (KNPR; Yukon, Canada) that underwent a severe 12-year population decline followed by a rapid rebound. We genotyped archival scales sampled pre-crash and contemporary fin clips collected post-crash, revealing high coverage (>90% average genotyping across all individuals) and low genotyping error (<0.01% within-libraries, 0.60% among-libraries) despite the relatively poor quality of recovered DNA. We observed slight decreases in expected heterozygosity, allelic diversity, and effective population size post-crash, but none were significant, suggesting genetic diversity was retained despite the severe demographic contraction. Genotypic data also revealed the genetic distinctiveness of a now extirpated population just outside of KNPR, revealing biodiversity loss at the northern edge of the species distribution. More broadly, we demonstrate GT-seq as a valuable tool for genome-wide data collection from archival samples to address basic questions in ecology and evolution, and inform applied research in wildlife conservation and fisheries management.</p>
Data from: No effect of environmental heterogeneity on the maintenance of genetic variation in wing shape in Drosophila melanogaster
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Data from: Behavioral types of predator and prey jointly determine prey survival: potential implications for the maintenance of within species behavioral variation
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Data from: Antagonistic pleiotropy in species with separate sexes, and the maintenance of genetic variation in life-history traits and fitness
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Allen Brain Atlas
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Annotated Behaviour and Observability Dataset (ABODe)
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