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32 results for “genetic effective population size”
Data for: Harvest and decimation affect genetic drift and the effective population size in wild reindeer
<p>Harvesting and culling are methods used to monitor and manage wildlife diseases. An important consequence of these practices is a change in the genetic dynamics of affected populations that may threaten their long-term viability. The effective population size (N<sub>e</sub>) is a fundamental parameter for describing such changes as it determines the amount of genetic drift in a population. Here, we estimate N<sub>e</sub> of a harvested wild reindeer population in Norway. Then we use simulations to investigate the genetic consequences of management efforts for handling a recent spread of chronic wasting disease, including increased adult male harvest and population decimation. The N<sub>e</sub>/N ratio in this population was found to be 0.124 at the end of the study period, compared to 0.239 in the preceding 14-year period. The difference was caused by increased harvest rates with a high proportion of adult males (older than 2.5 years) being shot (15.2 % in 2005-2018 and 44.8 % in 2021). Increased harvest rates decreased N<sub>e</sub> in the simulations, but less sex-biased harvest strategies had a lower negative impact. For harvest strategies that yield stable population dynamics, shifting the harvest from calves to adult males and females increased N<sub>e</sub>. Population decimation always resulted in decreased genetic variation in the population, with higher loss of heterozygosity and rare alleles with more severe decimation or longer periods of low population size. A very high proportion of males in the harvest had the most severe consequences for the loss of genetic variation. This study clearly shows how the effects of harvest strategies and changes in population size interact to determine the genetic drift of a managed population. The long-term genetic viability of wildlife populations subject to disease will also depend on the population impacts of the disease and how these interact with management actions.</p>
Whole genome demographic models indicate divergent effective population size histories shape contemporary genetic diversity gradients in a montane bumble bee
<p>Understanding historical range shifts and population size variation provides important context for interpreting contemporary genetic diversity. Methods to predict changes in species distributions and model changes in effective population size (N<sub>e</sub>) using whole genomes make it feasible to examine how temporal dynamics influence diversity across populations. We investigate N<sub>e</sub> variation and climate-associated range shifts to examine the origins of a previously observed latitudinal heterozygosity gradient in the bumble bee <em>Bombus</em> <em>vancouverensis</em> Cresson (Hymenoptera: Apidae: <em>Bombus</em> Latreille) in western North America. We analyze whole genomes from a latitude-elevation cline using sequentially Markovian coalescent models of N<sub>e</sub> through time to test whether relatively low diversity in southern high-elevation populations is a result of long-term differences in N<sub>e</sub>. We use Maxent models of the species range over the last 130,000 years to evaluate range shifts and stability. N<sub>e</sub> fluctuates with climate across populations, but more genetically diverse northern populations have maintained greater Ne over the late Pleistocene and experienced larger expansions with climatically favorable time periods. Northern populations also experienced larger bottlenecks during the last glacial period which matched the loss of range area near these sites, however, bottlenecks were not sufficient to erode diversity maintained during periods of large N<sub>e</sub>. A genome sampled from an island population indicated a severe postglacial bottleneck, indicating that large recent post-glacial declines are detectable if they have occurred. Genetic diversity was not related to niche stability or glacial-period bottleneck size. Instead, spatial expansions and increased connectivity during favorable climates likely maintain diversity in the north while restriction to high elevations maintains relatively low diversity despite greater stability in southern regions. Results suggest genetic diversity gradients reflect long-term differences in N<sub>e</sub> dynamics and also emphasize the unique effects of isolation on insular habitats for bumble bees. Patterns are discussed in the context of conservation under climate change.</p>
Data for: Harvest and decimation affect genetic drift and the effective population size in wild reindeer
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Whole genome demographic models indicate divergent effective population size histories shape contemporary genetic diversity gradients in a montane bumble bee
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Data from: Effective population size in a partially clonal plant is not predicted by the number of genetic individuals
<p>Estimating effective population size (<em>N</em><sub>e</sub>) is important for theoretical and practical applications in evolutionary biology and conservation. Nevertheless, estimates of <em>N</em><sub>e</sub> in organisms with complex life-history traits remain scarce because of the challenges associated with estimation methods. Partially clonal plants capable of both vegetative (clonal) growth and sexual reproduction are a common group of organisms for which the discrepancy between the apparent number of individuals (ramets) and the number of genetic individuals (genets) can be striking, and it is unclear how this discrepancy relates to <em>N</em><sub>e</sub>.</p> <p>In this study, we analysed two populations of the orchid <em>Cypripedium calceolus</em> to understand how the rate of clonal vs. sexual reproduction affected <em>N</em><sub>e</sub>. We genotyped >1,000 ramets at microsatellite and SNP loci, and estimated contemporary <em>N</em><sub>e</sub> with the linkage disequilibrium method, starting from the theoretical expectation that variance in reproductive success among individuals caused by clonal reproduction and by constraints on sexual reproduction would lower <em>N</em><sub>e</sub>. We considered factors potentially affecting our estimates, including different marker types and sampling strategies, and the influence of pseudoreplication in genomic datasets on <em>N</em><sub>e</sub> confidence intervals. The magnitude of <em>N</em><sub>e</sub>/<em>N</em><sub>ramets </sub>and <em>N</em><sub>e</sub>/<em>N</em><sub>genets</sub> ratios we provide may be used as reference points for other species with similar life-history traits. Our findings demonstrate that <em>N</em><sub>e</sub> in partially clonal plants cannot be predicted based on the number of genets generated by sexual reproduction, because demographic changes over time can strongly influence <em>N</em><sub>e</sub>. This is especially relevant in species of conservation concern, in which population declines may not be detected by only ascertaining the number of genets.</p>
Data from: Effective population size in a partially clonal plant is not predicted by the number of genetic individuals
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Data from: Stock enhancement or sea ranching? Insights from monitoring the genetic diversity, relatedness and effective size in a seeded great scallop population (Pecten maximus)
The mass release of hatchery-propagated stocks raises numerous questions concerning its efficiency in terms of local recruitment and effect on the genetic diversity of wild populations. A seeding program, consisting of mass release of hatchery-produced juveniles in the local naturally occurring population of great scallops (Pecten maximus L.), was initiated in the early 1980s in the Bay of Brest (France). The present study aims at evaluating whether this seeding program leads to actual population enhancement, with detectable effects on genetic diversity and effective population size, or consists of sea ranching with limited genetic consequences on the wild stock. To address this question, microsatellite-based genetic monitoring of three hatchery-born and naturally recruited populations was conducted over a 5-year period. Results showed a limited reduction in allelic richness but a strong alteration of allelic frequencies in hatchery populations, while genetic diversity appeared very stable over time in the wild populations. A temporal increase in relatedness was observed in both cultured stock and wild populations. Effective population size (Ne) estimates were low and variable in the wild population. Moreover, the application of the Ryman-Laikre model suggested a high contribution of hatchery-born scallops to the reproductive output of the wild population. Overall, the data suggest that the main objective of the seeding program, which is stock enhancement, is fulfilled. Moreover, gene flow from surrounding populations and/or the reproductive input of undetected sub-populations within the bay may buffer the Ryman-Laikre effect and ensure the retention of the local genetic variability.
Data from: Long-term isolation at a low effective population size greatly reduced genetic diversity in Gulf of California fin whales
The Gulf of California, Mexico is home to many cetacean species, including a presumed resident population of fin whales, Balaenoptera physalus. Past studies reported very low levels of genetic diversity among Gulf of California fin whales and a significant level of genetic differentiation from con-specifics in the eastern North Pacific. The aim of the present study was to assess the degree and timing of the isolation of Gulf of California fin whales in a population genetic analysis of 18 nuclear microsatellite genotypes from 402 samples and 565 mitochondrial control region DNA sequences (including mitochondrial sequences retrieved from NCBI). The analyses revealed that the Gulf of California fin whale population was founded ~2.3 thousand years ago and has since remained at a low effective population size (~360) and isolated from the eastern North Pacific (Nem between 0.89–1.4). The low effective population size and high degree of isolation implied that Gulf of California fin whales are vulnerable to the negative effects of genetic drift, human-caused mortality and habitat change.
Data from: Sex change and effective population size: implications for population genetic studies in marine fish
Large variance in reproductive success is the primary factor that reduces effective population size (Ne) in natural populations. In sequentially hermaphroditic (sex-changing) fish, the sex ratio is typically skewed and biased towards the 'first' sex, while reproductive success increases considerably after sex change. Therefore, sex-changing fish populations are theoretically expected to have lower Ne than gonochorists (separate sexes), assuming all other parameters are essentially equal. In this study, we estimate Ne from genetic data collected from two ecologically similar species living along the eastern coast of South Africa: one gonochoristic, the 'santer' sea bream Cheimerius nufar, and one protogynous (female-first) sex changer, the 'slinger' sea bream Chrysoblephus puniceus. For both species, no evidence of genetic structuring, nor significant variation in genetic diversity, was found in the study area. Estimates of contemporary Ne were significantly lower in the protogynous species, but the same pattern was not apparent over historical timescales. Overall, our results show that sequential hermaphroditism may affect Ne differently over varying time frames, and that demographic signatures inferred from genetic markers with different inheritance modes also need to be interpreted cautiously, in relation to sex-changing life histories.
Data from: Genetic structure in a fragmented Northern Hemisphere rainforest: large effective sizes and high connectivity among populations of the epiphytic lichen Lobaria pulmonaria
An extraordinary diversity of epiphytic lichens is found in the boreal rainforest of central Norway, the highest-latitude rainforest in the world. These rainforest relicts are located in ravine systems, and clear cutting has increased the distance between remaining patches. We hypothesized that the relatively small lichen populations in the remaining forest stands have suffered a depletion of genetic diversity through bottlenecks and founder events. In order to test this hypothesis we assessed genetic diversity and structure in populations of the tripartite lichen Lobaria pulmonaria using eight SSR loci. We sampled thalli growing on Picea abies branches and propagules deposited in snow at three localities. Contrary to expectations, we found high genetic diversity in lichen and snow samples, and high effective sizes of the studied populations. Also, limited genetic differentiation between populations, high historical migration rates, and a high proportion of first generation immigrants were estimated, implying high connectivity across distances <30 km. Almost all genetic variation was due to variation within sites; spatial genetic structures within populations were absent or appeared on small scales (5–10 m). The high genetic diversity in the remaining old boreal rainforests shows that even relict forest patches might be suitable for conservation of genetic diversity.
Data from: Temporal variation in genetic diversity and effective population size of Mediterranean and subalpine Arabidopsis thaliana populations
Currently there exists a limited knowledge on the extent of temporal variation in population genetic parameters of natural populations. Here we study the extent of temporal variation in population genetics by genotyping 151 genome-wide SNP markers polymorphic in 466 individuals collected from nine populations of the annual plant Arabidopsis thaliana during four years. Populations are located along an altitudinal climatic gradient from Mediterranean to subalpine environments in NE Spain, which has been shown to influence key demographic attributes and life-cycle adaptations. Genetically, A. thaliana populations were more variable across space than over time. Common multilocus genotypes were detected several years in the same population, whereas low-frequency multilocus genotypes appeared only one year. High-elevation populations were genetically poorer and more variable over time than low-elevation populations, which might be caused by a higher overall demographic instability at higher altitudes. Estimated effective population sizes were very low but also showed a significant decreasing trend with increasing altitude, suggesting a deeper impact of genetic drift at high-elevation populations. In comparison with single-year samplings, repeated genotyping over time captured substantially higher amount of genetic variation contained in A. thaliana populations. Furthermore, repeated genotyping of populations provided novel information on the genetic properties of A. thaliana populations and allowed hypothesizing on their underlying mechanisms. Therefore, including temporal genotyping programs into traditional population genetic studies can significantly increase our understanding of the dynamics of natural populations.
Simulation code for: Effects of population size change on the genetics of adaptation following an abrupt change in environment
<p>Since the rediscovery of Mendelian genetics over a century ago, there has been much debate about the evolutionary importance of mutations with large phenotypic effects. While population genetic models predict that large-effect mutations will typically contribute to adaptation following an abrupt change in environment, the prediction applies to populations of stable size and overlooks effects of population size change on adaptation (e.g., population decline following habitat loss; growth during range expansion). We evaluate the phenotypic and fitness effects of mutations contributing to adaptation immediately following an abrupt environmental shift that alters both selection and population size dynamics. We show that large-effect mutations are likely to contribute to adaptation in populations declining to a new carrying capacity, somewhat smaller-effect mutations contribute to evolutionary rescue, and small-effect mutations predominate in growing populations. We also show that the relative contributions of positively selected and overdominant mutations to adaptation depend on interactions between the phenotypic effect size distribution for new mutations and the specific form of population size change during adaptation (i.e., growth, decline, or evolutionary rescue). Our results illustrate how population size dynamics can shape the genetic basis of adaptation, which should motivate empirical comparisons of populations adapting in different demographic contexts.</p>
Data from: Genetic structure and effective population sizes in European red deer (Cervus elaphus) at a continental scale: insights from microsatellite DNA
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Data from: A century-long genetic record reveals that protist effective population sizes are comparable to those of macroscopic species
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Data from: Short-term genetic changes: evaluating effective population size estimates in a comprehensively described brown trout (Salmo trutta) population
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Data from: Temporal sampling helps unravel the genetic structure of naturally occurring populations of a phytoparasitic nematode. 1. Insights from the estimation of effective population sizes
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Data from: Genetic structure in a fragmented Northern Hemisphere rainforest: large effective sizes and high connectivity among populations of the epiphytic lichen Lobaria pulmonaria
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Simulation code for: Effects of population size change on the genetics of adaptation following an abrupt change in environment
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Data from: Temporal variation in genetic diversity and effective population size of Mediterranean and subalpine Arabidopsis thaliana populations
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Data from: Sex change and effective population size: implications for population genetic studies in marine fish
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