Theory predicts that genetic diversity and genetic differentiation may strongly vary among populations of the same species depending on population turnover and local population sizes. Yet, despite ...the importance of these predictions for evolutionary and conservation issues, empirical studies comparing high‐turnover and low‐turnover populations of the same species are scarce. In this study, we used Daphnia magna, a freshwater crustacean, as a model organism for such a comparison. In the southern/central part of its range, D. magna inhabits medium‐sized, stable ponds, whereas in the north, it occurs in small rock pools with strong population turnover. We found that these northern populations have a significantly lower genetic diversity and higher genetic differentiation compared to the southern/central populations. Total genetic diversity across populations was only about half and average within‐population diversity only about a third of that in southern/central populations. Moreover, an average southern population contains more genetic diversity than the whole metapopulation system in the north. We based our analyses both on silent sites and microsatellites. The similarity of our results despite the contrasting mutation rates of these markers suggests that the differences are caused by contemporary rather than by historical processes. Our findings show that variation in population turnover and population size may have a major impact on the genetic diversity and differentiation of populations, and hence may lead to differences in evolutionary processes like local adaptation, hybrid vigour and breeding system evolution in different parts of a species range.
Abstract
The field of noninvasive prenatal diagnosis (NIPD) has undergone significant progress over the last decade. Direct haplotyping has been successfully applied for NIPD of few single-gene ...disorders. However, technical issues remain for triplet-repeat expansions. The objective of this study was to develop an NIPD approach for couples at risk of transmitting dynamic mutations. This method includes targeted enrichment for linked-read libraries and targeted maternal plasma DNA sequencing. We also developed an innovative Bayesian procedure to integrate the Hoobari fetal genotyping model for inferring the fetal haplotype and the targeted gene variant status. Our method of directly resolving parental haplotypes through targeted linked-read sequencing was smoothly performed using blood samples from families with Huntington’s disease or myotonic dystrophy type 1. The Bayesian analysis of transmission of parental haplotypes allowed defining the genotype of five fetuses. The predicted variant status of four of these fetuses was in agreement with the invasive prenatal diagnosis findings. Conversely, no conclusive result was obtained for the NIPD of fragile X syndrome. Although improvements should be made to achieve clinically acceptable accuracy, our study shows that linked-read sequencing and parental haplotype phasing can be successfully used for NIPD of triplet-repeat expansion diseases.
Trial registration:
NCT04698551_date of first registration: 07/01/2021.
In Daphnia (Cladocera, Crustacea), parthenogenetic reproduction alternates with sexual reproduction. Individuals of both sexes that belong to the same parthenogenetic line are genetically identical, ...and their sex is determined by the environment. Previously, non-male producing (NMP) genotypes have been described in species of the Daphnia pulex group. Such genotypes can only persist through phases of sexual reproduction if they co-occur with normal (MP) genotypes that produce both males and females, and thus the breeding system polymorphism is similar to gynodioecy (coexistence of females with hermaphrodites), which is well known in plants. Here we show that the same breeding system polymorphism also occurs in Daphnia magna, a species that has diverged from D. pulex more than 100 MY ago. Depending on the population, between 0% and 40% of D. magna females do not produce males when experimentally exposed to a concentration of the putative sex hormone methyl farnesoate that normally leads to male-only clutches. Natural broods of these NMP females never contained males, contrasting with high proportions of male offspring in MP females from the same populations. The results from a series of crossing experiments suggest that NMP is determined by a dominant allele at a single nuclear locus (or a several closely linked loci): NMP × MP crosses always yielded 50% NMP and 50% MP offspring, whereas MP × MP crosses always yielded 100% MP offspring. Based on cytochrome c oxidase subunit I-sequences, we found that NMP genotypes from different populations belong to three highly divergent mitochondrial lineages, potentially representing three independent evolutionary origins of NMP in D. magna. Thus, the evolution of NMP genotypes in cyclical parthenogens may be more common than previously thought. Moreover, MP genotypes that coexist with NMP genotypes may have responded to the presence of the latter by partially specializing on male production. Hence, these populations of D. magna may be a model for an evolutionary transition from a purely environmental to a partially genetic sex determination system.
Atopic dermatitis (AD) is a highly prevalent chronic inflammatory skin disease representing a major source of global disability burden. Disease‐modifying therapies are showing promise in chronic ...inflammatory disorders such as rheumatoid arthritis and Crohn's disease with method and timing of initial treatment impacting long‐term disease outcomes. Whether disease‐modifying therapies, specifically those used as an early interventional approach, impacts disease course and comorbidity development in AD is not well‐understood. We reviewed the progress in disease modification strategies, emphasizing early intervention approaches in common (or proto‐typical) inflammatory diseases. Although more common in other fields, disease modification approaches are becoming increasingly investigated in dermatology, though studies in AD are lacking. Despite significant limitations in ongoing and completed studies, early data are promising and suggest that both the choice and timing of early intervention approach can affect long‐term disease course and comorbidity development. To best improve AD patient outcomes, more research is needed to further explore the impact of early disease‐modifying therapies. Future studies should focus on identifying the most effective approaches and extend the early results to a more inclusive set of comorbidities and longer‐term outcomes.
Balancing the formation and storage pressure with the storage capacity is one of the most significant steps toward developing H2 storage in hydrates. The large-cage occupancies of hydrogen molecules ...in tetrahydrofuran (THF), acetone, cyclohexanone (CHONE), and methylcyclohexane (MCH) hydrates were investigated by Raman spectroscopy, volumetric gas release measurement, and X-ray diffraction analysis in a pressure region below the equilibrium pressure of pure H2 hydrates at 255 ± 2 K. The results from the measurements show that H2 molecules occupy the large cage of the structure II THF+H2, acetone+H2, and CHONE+H2 hydrates at the suitable pressures and concentrations of promoter guest species, while H2 molecules do not occupy the largest cage of the structure H MCH+H2 hydrates, even around 70 MPa. The present work reveals that the large-cage occupancy of H2 strongly depends on the pressure and the concentration of promoter guest species. The maximum storage amount of H2 in the acetone+H2 hydrate was 3.6 ± 0.1 wt %, similar to that of THF+H2 hydrate, at 74 MPa and 255 ± 2 K. Acetone is superior to THF and CHONE as the promoter based on the relation between pressure and the large-cage occupancy of H2 molecules.
Familial hypocalciuric hypercalcemia (FHH) belongs to the disorders of a disturbed calcium homeostasis. Genetically, the disorder is inherited in an autosomal-dominant trait and represents an ...inactivating mutation of the calcium sensing receptor (CaSR) gene. We identified a Franconian kindred in which 6 individuals could be tested by molecular genetic means. In 5 individuals of 3 generations, the mutation could be classified as c.1697_1698delTG. This novel germline mutation creates a premature stop codon leading to a loss of 510 amino acids of the protein. The detection of CaSR gene mutations is suitable to differentiate states of hypercalcemia and may help to avoid invasive procedures such as parathyroidectomies.
Although there is little doubt that hosts evolve to reduce parasite damage, little is known about the evolutionary time scale on which host populations may adapt under natural conditions. Here we ...study the effects of selection by the microsporidian parasite Octosporea bayeri on populations of Daphnia magna. In a field study, we infected replicated populations of D. magna with the parasite, leaving control populations uninfected. After two summer seasons of experimental evolution (about 15 generations), the genetic composition of infected host populations differed significantly from the control populations. Experiments revealed that hosts from the populations that had evolved with the parasite had lower mortality on exposure to parasite spores and a higher competitive ability than hosts that had evolved without the parasite. In contrast, the susceptibility of the two treatment groups to another parasite, the bacterium Pasteuria ramosa, which was not present during experimental evolution of the populations, did not differ. Fitness assays in the absence of parasites revealed a higher fitness for the control populations, but only under low population density with high resource availability. Overall, our results show that, under natural conditions, Daphnia populations are able to adapt rapidly to the prevailing conditions and that this evolutionary change is specific to the environment.
Parthenogenesis (reproduction through unfertilized eggs) encompasses a variety of reproduction modes with (automixis) or without (apomixis) meiosis. Different modes of automixis have very different ...genetic and evolutionary consequences but can be particularly difficult to tease apart. In this study, we propose a new method to discriminate different types of automixis from population‐level genetic data. We apply this method to diploid Artemia parthenogenetica, a crustacean whose reproductive mode remains controversial despite a century of intensive cytogenetic observations. We focus on A. parthenogenetica from two western Mediterranean populations. We show that they are diploid and that markers remain heterozygous in cultures maintained up to ~36 generations in the laboratory. Moreover, parallel patterns of population‐wide heterozygosity levels between the two natural populations strongly support the conclusion that diploid A. parthenogenetica reproduce by automictic parthenogenesis with central fusion and low, but nonzero recombination. This settles a century‐old controversy on Artemia, and, more generally, suggests that many automictic organisms harbour steep within‐chromosome gradients of heterozygosity due to a transition from clonal transmission in centromere‐proximal regions to a form of inbreeding similar to self‐fertilization in centromere‐distal regions. Such systems therefore offer a new avenue for contrasting the genomic consequences of asexuality and inbreeding.
Inbreeding adversely affects life history traits as well as various other fitness‐related traits, but its effect on cognitive traits remains largely unexplored, despite their importance to fitness of ...many animals under natural conditions. We studied the effects of inbreeding on aversive learning (avoidance of an odour previously associated with mechanical shock) in multiple inbred lines of Drosophila melanogaster derived from a natural population through up to 12 generations of sib mating. Whereas the strongly inbred lines after 12 generations of inbreeding (0.75 < F < 0.93) consistently showed reduced egg‐to‐adult viability (on average by 28%), the reduction in learning performance varied among assays (average = 18% reduction), being most pronounced for intermediate conditioning intensity. Furthermore, moderately inbred lines (F = 0.38) showed no detectable decline in learning performance, but still had reduced egg‐to‐adult viability, which indicates that overall inbreeding effects on learning are mild. Learning performance varied among strongly inbred lines, indicating the presence of segregating variance for learning in the base population. However, the learning performance of some inbred lines matched that of outbred flies, supporting the dominance rather than the overdominance model of inbreeding depression for this trait. Across the inbred lines, learning performance was positively correlated with the egg‐to‐adult viability. This positive genetic correlation contradicts a trade‐off observed in previous selection experiments and suggests that much of the genetic variation for learning is owing to pleiotropic effects of genes affecting functions related to survival. These results suggest that genetic variation that affects learning specifically (rather than pleiotropically through general physiological condition) is either low or mostly due to alleles with additive (semi‐dominant) effects.
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