Parasite-driven replacement of a sexual by a closely related asexual taxon in nature

Asexual species are thought to suffer more from coevolving parasites than related sexuals. Yet a variety of studies do not find the patterns predicted by theory. Here, to shine light on this conundrum, we investigate one such case of an asexual advantage in the presence of parasites. We follow the frequency dynamics of sexual and asexualDaphnia pulexin a natural pond that was initially dominated by sexuals. Coinciding with an epidemic of a microsporidian parasite infecting both sexuals and asexuals, the pond was rapidly taken over by the initially rare asexuals. With experiments comparing multiple sexual and asexual clones from across the local metapopulation, we confirm that asexuals are less susceptible and also suffer less from the parasite once infected. These results are consistent with the parasite-driven, ecological replacement of dominant sexuals by closely related, but more resistant asexuals, ultimately leading to the extinction of the formerly superior sexual competitor. Our study is one of the clearest examples from nature, backed up by experimental verification, showing a parasite-mediated reversal of competition dynamics. The experiments show that, across the metapopulation, asexuals have an advantage in the presence of parasites. In this metapopulation, asexuals are relatively rare, likely due to their recent invasion. While we cannot rule out other reasons for the observed patterns, the results are consistent with a temporary parasite-mediated advantage of asexuals due to the fact that they are rare, which is an underappreciated aspect of the Red Queen Hypothesis.Peer reviewe

Reduced lifespan and increased ageing driven by genetic drift in small populations

Explaining the strong variation in lifespan among organisms remains a major challenge in evolutionary biology. Whereas previous work has concentrated mainly on differences in selection regimes and selection pressures, we hypothesize that differences in genetic drift may explain some of this variation. We develop a model to formalize this idea and show that the strong positive relationship between lifespan and genetic diversity predicted by this model indeed exists among populations of Daphnia magna, and that ageing is accelerated in small populations. Additional results suggest that this is due to increased drift in small populations rather than adaptation to environments favoring faster life histories. First, the correlation between genetic diversity and lifespan remains significant after statistical correction for potential environmental covariates. Second, no trade-offs are observed; rather, all investigated traits show clear signs of increased genetic load in the small populations. Third, hybrid vigor with respect to lifespan is observed in crosses between small but not between large populations. Together, these results suggest that the evolution of lifespan and ageing can be strongly affected by genetic drift, especially in small populations, and that variation in lifespan and ageing may often be nonadaptive, due to a strong contribution from mutation accumulation

Quality improvement, implementation, and dissemination strategies to improve mental health care for children and adolescents: a systematic review

Abstract Background Some outcomes for children with mental health problems remain suboptimal because of poor access to care and the failure of systems and providers to adopt established quality improvement strategies and interventions with proven effectiveness. This review had three goals: (1) assess the effectiveness of quality improvement, implementation, and dissemination strategies intended to improve the mental health care of children and adolescents; (2) examine harms associated with these strategies; and (3) determine whether effectiveness or harms differ for subgroups based on system, organizational, practitioner, or patient characteristics. Methods Sources included MEDLINE®, the Cochrane Library, PsycINFO, and CINAHL, from database inception through February 17, 2017. Additional sources included gray literature, additional studies from reference lists, and technical experts. Two reviewers selected relevant randomized controlled trials (RCTs) and observational studies, extracted data, and assessed risk of bias. Dual analysis, synthesis, and grading of the strength of evidence for each outcome followed for studies meeting inclusion criteria. We also used qualitative comparative analysis to examine relationships between combinations of strategy components and improvements in outcomes. Results We identified 18 strategies described in 19 studies. Eleven strategies significantly improved at least one measure of intermediate outcomes, final health outcomes, or resource use. Moderate strength of evidence (from one RCT) supported using provider financial incentives such as pay for performance to improve the competence with which practitioners can implement evidence-based practices (EBPs). We found inconsistent evidence involving strategies with educational meetings, materials, and outreach; programs appeared to be successful in combination with reminders or providing practitioners with newly collected clinical information. We also found low strength of evidence for no benefit for initiatives that included only educational materials or meetings (or both), or only educational materials and outreach components. Evidence was insufficient to draw conclusions on harms and moderators of interventions. Conclusions Several strategies can improve both intermediate and final health outcomes and resource use. This complex and heterogeneous body of evidence does not permit us to have a high degree of confidence about the efficacy of any one strategy because we generally found only a single study testing each strategy. Trial registration PROSPERO, CRD42015024759

Elevated protein concentrations in newborn blood and the risks of autism spectrum disorder, and of social impairment, at age 10 years among infants born before the 28th week of gestation

Among the 1 of 10 children who are born preterm annually in the United States, 6% are born before the third trimester. Among children who survive birth before the 28th week of gestation, the risks of autism spectrum disorder (ASD) and non-autistic social impairment are severalfold higher than in the general population. We examined the relationship between top quartile inflammation-related protein concentrations among children born extremely preterm and ASD or, separately, a high score on the Social Responsiveness Scale (SRS total score ≥65) among those who did not meet ASD criteria, using information only from the subset of children whose DAS-II verbal or non-verbal IQ was ≥70, who were assessed for ASD, and who had proteins measured in blood collected on ≥2 days (N = 763). ASD (N = 36) assessed at age 10 years is associated with recurrent top quartile concentrations of inflammation-related proteins during the first post-natal month (e.g., SAA odds ratio (OR); 95% confidence interval (CI): 2.5; 1.2–5.3) and IL-6 (OR; 95% CI: 2.6; 1.03–6.4)). Top quartile concentrations of neurotrophic proteins appear to moderate the increased risk of ASD associated with repeated top quartile concentrations of inflammation-related proteins. High (top quartile) concentrations of SAA are associated with elevated risk of ASD (2.8; 1.2–6.7) when Ang-1 concentrations are below the top quartile, but not when Ang-1 concentrations are high (1.3; 0.3–5.8). Similarly, high concentrations of TNF-α are associated with heightened risk of SRS-defined social impairment (N = 130) (2.0; 1.1–3.8) when ANG-1 concentrations are not high, but not when ANG-1 concentrations are elevated (0.5; 0.1–4.2)

Prior residency does not always pay off – co-infections in Daphnia

The epidemiological and ecological processes which govern the success of multiple-species co-infections are as yet unresolved. Here we investigated prior versus late residency within hosts, meaning which parasite contacts the host first, to determine if the outcomes of intra-host competition are altered. We infected a single genotype of the waterflea Daphnia galeata with both the intestinal protozoan Caullerya mesnili and the haemolymph fungus Metschnikowia sp. (single genotype of each parasite species), as single infections, simultaneous co-infections and as sequential co-infections, with each parasite given 4 days prior residency. Simultaneous co-infections were significantly more virulent than both single infections and sequential co-infections, as measured by a decreased host life span and fecundity. Further, in addition to the Daphnia host, the parasites also suffered fitness decreases in simultaneous co-infections, as measured by spore production. The sequential co-infections, however, had mixed effects: C. mesnili benefited from prior residency, whereas Metschnikowia sp. experienced a decline in fitness. Our results show that multiple-species co-infections of Daphnia may be more virulent than single infections, and that prior residency does not always provide a competitive advantage

A daphnia parasite (Caullerya mesnili) constitutes a new member of the ichthyosporea, a group of protists near the animal - fungi divergence

Caullerya mesnili is a protozoan endoparasite in the gut epithelium of Daphnia, which causes regular epidemics in lakes throughout Europe. Its classification has remained unchanged for over a century, leaving it placed with the Haplosporidia, despite speculation that this position is incorrect. The difficulty in classifying C. mesnili stems from its few known morphological and ecological characteristics, as well as a lack of genetic markers. Here we sequenced the nuclear small subunit (SSU) and internal transcribed spacer rDNA regions of C. mesnili samples from 10 locations. Based on sequence similarities, we suggest the re-classification of C. mesnili to the Ichthyosporea, a class of protists near the animal–fungi divergence. We report average intragenomic variation of 0.75% and 2.27% in the SSU and internal transcribed spacer regions, respectively. From electron micrographs and light microscopy of histological sections we determined that C. mesnili spores grow within the intestinal epithelium where they establish themselves intercellularly. In addition, we confirmed previous accounts regarding the high virulence of this parasite. Caullerya mesnili reduces host lifespan, the number of clutches, and the total number of offspring. This high selection pressure placed on hosts supports the importance of C. mesnili as a model parasite for the study of host–parasite biology in permanent lakes

Data from: Genetic load, inbreeding depression and hybrid vigor covary with population size: an empirical evaluation of theoretical predictions

Reduced population size is thought to have strong consequences for evolutionary processes as it enhances the strength of genetic drift. In its interaction with selection, this is predicted to increase the genetic load, reduce inbreeding depression, and increase hybrid vigour, and in turn affect phenotypic evolution. Several of these predictions have been tested, but comprehensive studies controlling for confounding factors are scarce. Here we show that populations of Daphnia magna, which vary strongly in genetic diversity, also differ in genetic load, inbreeding depression, and hybrid vigor in a way that strongly supports theoretical predictions: Inbreeding depression is positively correlated with genetic diversity (a proxy for Ne), and genetic load and hybrid vigour are negatively correlated with genetic diversity. These patterns remain significant after accounting for potential confounding factors and indicate that, in small populations, a large proportion of the segregation load is converted into fixed load. Overall, the results suggest that the nature of genetic variation for fitness-related traits differs strongly between large and small populations. This has large consequences for evolutionary processes in natural populations, such as selection on dispersal, breeding systems, ageing, and local adaptation

Data from: Reduced lifespan and increased ageing driven by genetic drift in small populations

Explaining the strong variation in lifespan among organisms remains a major challenge in evolutionary biology. Whereas previous work has concentrated mainly on differences in selection regimes and selection pressures, we hypothesize that differences in genetic drift may explain some of this variation. We develop a model to formalize this idea and show that the strong positive relationship between lifespan and genetic diversity predicted by this model indeed exists among populations of Daphnia magna, and that ageing is accelerated in small populations. Additional results suggest that this is due to increased drift in small populations rather than adaptation to environments favoring faster life histories: First, the correlation between genetic diversity and lifespan remains significant after statistical correction for potential environmental covariates. Second, no trade-offs are observed; rather, all investigated traits show clear signs of increased genetic load in the small populations. Third, hybrid vigor with respect to lifespan is observed in crosses between small but not between large populations. Together, these results suggest that the evolution of lifespan and ageing can be strongly affected by genetic drift, especially in small populations, and that variation in lifespan and ageing may often be non-adaptive, due to a strong contribution from mutation accumulation to this variation

age1

results of first life table experimen

age2

results of second life table experimen