Meta-evaluation of meta-analysis: ten appraisal questions for biologists

Effect of ginger in the treatment of nausea and vomiting compared with vitamin B6 and placebo during pregnancy: a meta-analysis

INTRODUCTION

Nausea and vomiting (NV) affect up to 85% of pregnant women, which has multiple effects on pregnancy outcome. The truth etiology of nausea and vomiting in pregnancy (NVP) is still unknown. Considering the potential teratogenic effect in fetus due to chemical drugs, ginger can be used to treat nausea and vomiting during pregnancy. Reports have shown that ginger can reduce the severity of NV, however, these results are controversial. Therefore, this meta-analysis aims to explore the effect of ginger in the treatment of nausea and vomiting during pregnancy compared with placebo and vitamin B6.

METHODS

The randomized control trials (RCTs) on the association with ginger and pregnancy-related nausea and vomiting were searched and identified in two databases Web of Science and PubMed (up to April 2019). Stata software was used to conduct meta-analysis. In addition, the source of heterogeneity explored by metaregression, sensitivity analysis, subgroup analyses, the publication bias were assessed by Egger's tests and Funnel plot, p < .05 was considered to be significant.

RESULTS

Thirteen studies involving 1174 subjects were included in this meta-analysis. The result demonstrated that ginger intervention has significant effect in improving general symptom of NVP [OR = 7.475, 95% CI = (4.133, 13.520), I2 = 30.1%], relieving severity of nausea [SMD = 0.821, 95% CI = (0.585, 1.056), I2 = 38.9%], but not significant in reducing vomiting [SMD = 0.549, 95% CI = (-0.268, 1.365), I2 = 91.4%], compared with placebo. Besides, ginger intervention has no significant effect on improving general symptom of NVP [OR = 1.239, 95% CI = (0.495, 3.102), I2 = 57.3%], relieving severity of nausea [SMD = 0.199, 95% CI = (-0.102, 0.500), I2 = 65.7%], reducing vomiting [SMD = 0.331, 95% CI = (-0.145, 0.808), I2 = 85.9%], compared with vitamin B6.

CONCLUSIONS

Ginger supplementation significantly relieve general NVP symptom and nausea compared with placebo, but no significant effect on vomiting. Moreover, ginger is more effective than vitamin B6 in treating NVP, although, there were no significant differences. Further, rigidly designed RCTs with larger sample sizes are needed to verify the effectiveness of ginger supplementation for treatment NVP compared with vitamin B6.

Localizing the human brain response to olfactory stimulation: A meta-analytic approach

The human sense of smell and the ability to detect and distinguish odors allows for the extraction of valuable information from the environment, thereby driving human behavior. Not only can the sense of smell help to monitor the safety of inhaled air, but it can also help to evaluate the edibility of food. Therefore, in an effort to further our understanding of the human sense of smell, the aim of this meta-analysis was to provide the scientific community with activation probability maps of the functional anatomy of the olfactory system, in addition to separate activation maps for specific odor categories (pleasant, food, and aversive odors). The activation likelihood estimation (ALE) method was utilized to quantify all relevant and available data to perform a formal statistical analysis on the inter-study concordance of various odor categories. A total of 81 studies (108 contrasts, 1053 foci) fulfilled our inclusion criteria. Significant ALE peaks were observed in all odor categories in brain areas typically associated with the functional neuroanatomy of olfaction including the piriform cortex, amygdala, insula, and orbitofrontal cortex, amongst others. Additional contrast analyses indicate clear differences in neural activation patterns between odor categories.

A meta-analysis of sex differences in animal personality: no evidence for the greater male variability hypothesis

The notion that men are more variable than women has become embedded into scientific thinking. For mental traits like personality, greater male variability has been partly attributed to biology, underpinned by claims that there is generally greater variation among males than females in non-human animals due to stronger sexual selection on males. However, evidence for greater male variability is limited to morphological traits, and there is little information regarding sex differences in personality-like behaviours for non-human animals. Here, we meta-analysed sex differences in means and variances for over 2100 effects (204 studies) from 220 species (covering five broad taxonomic groups) across five personality traits: boldness, aggression, activity, sociality and exploration. We also tested if sexual size dimorphism, a proxy for sex-specific sexual selection, explains variation in the magnitude of sex differences in personality. We found no significant differences in personality between the sexes. In addition, sexual size dimorphism did not explain variation in the magnitude of the observed sex differences in the mean or variance in personality for any taxonomic group. In sum, we find no evidence for widespread sex differences in variability in non-human animal personality.

Biodiversity promotes ecosystem functioning despite environmental change

Three decades of research have demonstrated that biodiversity can promote the functioning of ecosystems. Yet, it is unclear whether the positive effects of biodiversity on ecosystem functioning will persist under various types of global environmental change drivers. We conducted a meta‐analysis of 46 factorial experiments manipulating both species richness and the environment to test how global change drivers (i.e. warming, drought, nutrient addition or CO₂ enrichment) modulated the effect of biodiversity on multiple ecosystem functions across three taxonomic groups (microbes, phytoplankton and plants). We found that biodiversity increased ecosystem functioning in both ambient and manipulated environments, but often not to the same degree. In particular, biodiversity effects on ecosystem functioning were larger in stressful environments induced by global change drivers, indicating that high‐diversity communities were more resistant to environmental change. Using a subset of studies, we also found that the positive effects of biodiversity were mainly driven by interspecific complementarity and that these effects increased over time in both ambient and manipulated environments. Our findings support biodiversity conservation as a key strategy for sustainable ecosystem management in the face of global environmental change.

Differences in resource acquisition, not allocation, mediate the relationship between behaviour and fitness: a systematic review and meta-analysis

Within populations, individuals often show repeatable variation in behaviour, called 'animal personality'. In the last few decades, numerous empirical studies have attempted to elucidate the mechanisms maintaining this variation, such as life-history trade-offs. Theory predicts that among-individual variation in behavioural traits could be maintained if traits that are positively associated with reproduction are simultaneously associated with decreased survival, such that different levels of behavioural expression lead to the same net fitness outcome. However, variation in resource acquisition may also be important in mediating the relationship between individual behaviour and fitness components (survival and reproduction). For example, if certain phenotypes (e.g. dominance or aggressiveness) are associated with higher resource acquisition, those individuals may have both higher reproduction and higher survival, relative to others in the population. When individuals differ in their ability to acquire resources, trade-offs are only expected to be observed at the within-individual level (i.e. for a given amount of resource, if an individual increases its allocation to reproduction, it comes at the cost of allocation to survival, and vice versa), while among individuals traits that are associated with increased survival may also be associated with increased reproduction. We performed a systematic review and meta-analysis, asking: (i) do among-individual differences in behaviour reflect among-individual differences in resource acquisition and/or allocation, and (ii) is the relationship between behaviour and fitness affected by the type of behaviour and the testing environment? Our meta-analysis consisted of 759 estimates from 193 studies. Our meta-analysis revealed a positive correlation between pairs of estimates using both survival and reproduction as fitness proxies. That is, for a given study, behaviours that were associated with increased reproduction were also associated with increased survival, suggesting that variation in behaviour at the among-individual level largely reflects differences among individuals in resource acquisition. Furthermore, we found the same positive correlation between pairs of estimates using both survival and reproduction as fitness proxies at the phenotypic level. This is significant because we also demonstrated that these phenotypic correlations primarily reflect within-individual correlations. Thus, even when accounting for among-individual differences in resource acquisition, we did not find evidence of trade-offs at the within-individual level. Overall, the relationship between behaviour and fitness proxies was not statistically different from zero at the among-individual, phenotypic, and within-individual levels; this relationship was not affected by behavioural category nor by the testing condition. Our meta-analysis highlights that variation in resource acquisition may be more important in driving the relationship between behaviour and fitness than previously thought, including at the within-individual level. We suggest that this may come about via heterogeneity in resource availability or age-related effects, with higher resource availability and/or age leading to state-dependent shifts in behaviour that simultaneously increase both survival and reproduction. We emphasize that future studies examining the mechanisms maintaining behavioural variation in populations should test the link between behavioural expression and resource acquisition - both within and among individuals. Such work will allow the field of animal personality to develop specific predictions regarding the mediating effect of resource acquisition on the fitness consequences of individual behaviour.

Costs of territoriality: a review of hypotheses, meta-analysis, and field study

The evolution of territoriality reflects the balance between the benefit and cost of monopolising a resource. While the benefit of territoriality is generally intuitive (improved access to resources), our understanding of its cost is less clear. This paper combines: 1. a review of hypotheses and meta-analytic benchmarking of costs across diverse taxa; and 2. a new empirical test of hypotheses using a longitudinal study of free-living male territorial lizards. The cost of territoriality was best described as a culmination of multiple factors, but especially costs resulting from the time required to maintain a territory (identified by the meta-analysis) or those exacerbated by a territory that is large in size (identified by the empirical test). The meta-analysis showed that physiological costs such as energetic expenditure or stress were largely negligible in impact on territory holders. Species that used territories to monopolise access to mates appeared to incur the greatest costs, whereas those defending food resources experienced the least. The single largest gap in our current understanding revealed by the literature review is the potential cost associated with increased predation. There is also a clear need for multiple costs to be evaluated concurrently in a single species. The empirical component of this study showcases a powerful analytical framework for evaluating a range of hypotheses using correlational data obtained in the field. More broadly, this paper highlights key factors that should be considered in any investigation that attempts to account for the evolutionary origin or ecological variation in territorial behaviour within and between species.

Contrasting effects of mammal grazing on foliar fungal diseases: patterns and potential mechanisms

Plant pathogens and their hosts often coexist with mammal grazers. However, the direction and strength of grazing effects on foliar fungal diseases can be idiosyncratic, varying among host plant species and pathogen types. We combined a 6 yr yak-grazing experiment, a clipping experiment simulating different mammal consumption patterns (leaf damage vs whole-leaf removal), and a meta-analysis of 63 comparisons to evaluate how grazing impacts foliar fungal diseases across plant growth types (grass vs forb) and pathogen life histories (biotroph vs necrotroph). In the yak-grazing experiment, grazing had no significant effect on disease severity, and grasses experienced a higher disease severity than forbs; there was a significant interaction between pathogen type and grazing. In both the yak-grazing experiment and meta-analysis, grazing decreased biotrophic pathogens (mainly rusts and powdery mildew), but did not affect necrotrophic pathogens (mainly leaf spots). The clipping experiment suggested that grazers might promote infection by necrotrophic pathogens by producing wounds on leaves, but inhibit biotrophic pathogens via leaf removal. In conclusion, our three-part approach revealed that intrinsic properties of both plants and pathogens shape patterns of disease in natural ecosystems, greatly improving our ability to predict disease severity under mammal grazing.

Preferred reporting items for systematic reviews and meta-analyses in ecology and evolutionary biology: a PRISMA extension

Since the early 1990s, ecologists and evolutionary biologists have aggregated primary research using meta-analytic methods to understand ecological and evolutionary phenomena. Meta-analyses can resolve long-standing disputes, dispel spurious claims, and generate new research questions. At their worst, however, meta-analysis publications are wolves in sheep's clothing: subjective with biased conclusions, hidden under coats of objective authority. Conclusions can be rendered unreliable by inappropriate statistical methods, problems with the methods used to select primary research, or problems within the primary research itself. Because of these risks, meta-analyses are increasingly conducted as part of systematic reviews, which use structured, transparent, and reproducible methods to collate and summarise evidence. For readers to determine whether the conclusions from a systematic review or meta-analysis should be trusted - and to be able to build upon the review - authors need to report what they did, why they did it, and what they found. Complete, transparent, and reproducible reporting is measured by 'reporting quality'. To assess perceptions and standards of reporting quality of systematic reviews and meta-analyses published in ecology and evolutionary biology, we surveyed 208 researchers with relevant experience (as authors, reviewers, or editors), and conducted detailed evaluations of 102 systematic review and meta-analysis papers published between 2010 and 2019. Reporting quality was far below optimal and approximately normally distributed. Measured reporting quality was lower than what the community perceived, particularly for the systematic review methods required to measure trustworthiness. The minority of assessed papers that referenced a guideline (~16%) showed substantially higher reporting quality than average, and surveyed researchers showed interest in using a reporting guideline to improve reporting quality. The leading guideline for improving reporting quality of systematic reviews is the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) statement. Here we unveil an extension of PRISMA to serve the meta-analysis community in ecology and evolutionary biology: PRISMA-EcoEvo (version 1.0). PRISMA-EcoEvo is a checklist of 27 main items that, when applicable, should be reported in systematic review and meta-analysis publications summarising primary research in ecology and evolutionary biology. In this explanation and elaboration document, we provide guidance for authors, reviewers, and editors, with explanations for each item on the checklist, including supplementary examples from published papers. Authors can consult this PRISMA-EcoEvo guideline both in the planning and writing stages of a systematic review and meta-analysis, to increase reporting quality of submitted manuscripts. Reviewers and editors can use the checklist to assess reporting quality in the manuscripts they review. Overall, PRISMA-EcoEvo is a resource for the ecology and evolutionary biology community to facilitate transparent and comprehensively reported systematic reviews and meta-analyses.

Positive but variable effects of crop diversification on biodiversity and ecosystem services

Ecological theory suggests that biodiversity has a positive and stabilizing effect on the delivery of ecosystem services. Yet, the impacts of increasing the diversity of cultivated crop species or varieties in agroecosystems are still under scrutiny. The available empirical evidence is scattered in scope, agronomic and geographic contexts, and impacts on ecosystem services may depend on the type of diversification strategy used. To robustly assess the effects of crop diversification in agroecosystems, we compiled the results of 95 meta-analyses integrating 5156 experiments conducted over 84 experimental years and representing more than 54,500 paired observations on 120 crop species in 85 countries. Overall, our synthesis of experimental data from across the globe shows that crop diversification enhances not only crop production (median effect +14%) but also the associated biodiversity (+24%, i.e., the biodiversity of non-cultivated plants and animals), and several supporting and regulating ecosystem services including water quality (+51%), pest and disease control (+63%) and soil quality (+11%). However, there was substantial variability in the results for each individual ecosystem service between different diversification strategies such as agroforestry, intercropping, cover crops, crop rotation or variety mixtures. Agroforestry is particularly effective in delivering multiple ecosystem services, that is, water regulation and quality, pest and diseases regulation, associated biodiversity, long-term soil productivity and quality. Variety mixtures, instead, provide the lowest benefits, whereas the other strategies show intermediate results. Our results highlight that while increasing the diversity of cultivated crop species or varieties in agroecosystems represents a very promising strategy for more sustainable land management, contributing to enhanced yields, enhanced biodiversity and ecosystem services, some crop diversification strategies are more effective than others in supporting key ecosystem services.

Are Demethylation Inhibitor Plus Quinone Outside Inhibitor Fungicide Premixes During Flowering Worthwhile for Fusarium Head Blight Control in Wheat? A Meta-Analysis

Fusarium head blight (FHB), caused mainly by Fusarium graminearum, is best controlled with demethylation inhibitor (DMI) fungicides during flowering. However, the use of premixes of DMI and quinone outside inhibitor (QoI) fungicides to control FHB has increased in Brazil. Data on FHB severity and wheat yields measured in field experiments conducted in Brazil were gathered from both peer- and nonpeer-reviewed sources published from 2000 to 2018. After selection criteria were applied, 73 field trials from 35 bibliographic sources were identified, among which 50% of the data were obtained from cooperative network trials conducted after 2011. To be included in the analysis, DMI plus QoI premixes or tebuconazole were tested in at least 14 trials and 3 years. Four premixes met the criteria. Estimates of percent control (and respective 95% confidence intervals) by a network model fitted to the log of the treatment means ranged from 44.1% (pyraclostrobin plus metconazole applied once; 32.4 to 53.7) to 64.3% (pyraclostrobin plus metconazole; 58.4 to 69.3); the latter did not differ from tebuconazole (59.9%; 53.6 to 65.3). Yield response was statistically similar for pyraclostrobin plus metconazole (532.1 kg/ha; 441 to 623) and trifloxystrobin plus prothioconazole (494.9 kg/ha; 385 to 551), and both differed statistically from a group composed of tebuconazole (448.2 kg/ha; 342 to 554), trifloxystrobin plus tebuconazole (468.2 kg/ha; 385 to 551), azoxystrobin plus tebuconazole (462.4 kg/ha; 366 to 558), and pyraclostrobin plus metconazole applied once (413.7 kg/ha; 308 to 518). The two categories of FHB index (7% cutoff) and yield (3,000 kg/ha cutoff), both in the nontreated check, did not explain the heterogeneity in the estimates. Considering only the fungicide effects on yield, two sequential sprays of tebuconazole or one spray of pyraclostrobin plus metconazole as management choices are likely more profitable than DMI plus QoI premixes sprayed twice during flowering.

Drought has negative consequences on aphid fitness and plant vigor: Insights from a meta-analysis

Aphids are abundant in natural and managed vegetation, supporting a diverse community of organisms and causing damage to agricultural crops. Due to a changing climate, periods of drought are anticipated to increase, and the potential consequences of this for aphid-plant interactions are unclear.Using a meta-analysis and synthesis approach, we aimed to advance understanding of how increased drought incidence will affect this ecologically and economically important insect group and to characterize any potential underlying mechanisms. We used qualitative and quantitative synthesis techniques to determine whether drought stress has a negative, positive, or null effect on aphid fitness and examined these effects in relation to (a) aphid biology, (b) geographical region, and (c) host plant biology.Across all studies, aphid fitness is typically reduced under drought. Subgroup analysis detected no difference in relation to aphid biology, geographical region, or the aphid-plant combination, indicating the negative effect of drought on aphids is potentially universal. Furthermore, drought stress had a negative impact on plant vigor and increased plant concentrations of defensive chemicals, suggesting the observed response of aphids is associated with reduced plant vigor and increased chemical defense in drought-stressed plants.We propose a conceptual model to predict drought effects on aphid fitness in relation to plant vigor and defense to stimulate further research.

A meta-analysis of the ecological and economic outcomes of mangrove restoration

Mangrove restoration has become a popular strategy to ensure the critical functions and economic benefits of this ecosystem. This study conducts a meta-analysis of the peer-reviewed literature on the outcomes of mangrove restoration. On aggregate, restored mangroves provide higher ecosystem functions than unvegetated tidal flats but lower than natural mangrove stands (respectively RR' = 0.43, 95%CIs = 0.23 to 0.63; RR' = -0.21, 95%CIs = -0.34 to -0.08), while they perform on par with naturally-regenerated mangroves and degraded mangroves. However, restoration outcomes vary widely between functions and comparative bases, and are mediated by factors such as restoration age, species, and restoration method. Furthermore, mangrove restoration offers positive benefit-cost ratios ranging from 10.50 to 6.83 under variable discount rates (-2% to 8%), suggesting that mangrove restoration is a cost-effective form of ecosystem management. Overall, the results suggest that mangrove restoration has substantial potential to contribute to multiple policy objectives related to biodiversity conservation, climate change mitigation and sustainable development.

An assessment of statistical methods for non-independent data in ecological meta-analyses: Comment

Recently, Song et al. (2020) conducted a simulation study using different methods to deal with non-independence resulting from effect sizes originating from the same paper - a common occurrence in ecological meta-analyses. The main methods that were of interest in their simulations were: 1) a standard random-effects model used in combination with a weighted average effect size for each paper (i.e., a two-step method), 2) a standard random-effects model after randomly choosing one effect size per paper, 3) a multilevel (hierarchical) meta-analysis model, modelling paper identity as a random factor, and 4) a meta-analysis making use of a robust variance estimation method. Based on their simulation results, they recommend that meta-analysts should either use the two-step method, which involves taking a weighted paper mean followed by analysis with a random-effects model, or the robust variance estimation method.

Efficacy thresholds for clinical trials with advanced or metastatic leiomyosarcoma patients: A European Organisation for Research and Treatment of Cancer Soft Tissue and Bone Sarcoma Group meta-analysis based on a literature review for soft-tissue sarcomas

BACKGROUND

In 2002, the European Organisation for Research and Treatment of Cancer Soft Tissue and Bone Sarcoma Group reported well-established values for conducting phase II trials for soft-tissue sarcomas. An update is provided for leiomyosarcoma (LMS).

MATERIALS AND METHODS

Clinical trials with advanced or metastatic LMS were identified via literature review in PubMed (published 2003-2018, ≥10 adult LMS patients). End-points were 3- and 6-month progression-free survival rates (PFSR-3m and PFSR-6m). When estimates could not be derived from publications, data requests were sent out. Treatments were classified as recommended (R-T) or non-recommended (NR-T) according to the ESMO 2018 guidelines. A random effects meta-analysis was used to pool trial-specific estimates for first-line (1L) or pre-treated (2L+) patients separately. The ESMO Magnitude of Clinical Benefit Scale was used to guide the treatment effect to target in future trials.

RESULTS

From 47 studies identified, we obtained information on 7 1L and 16 2L+ trials for 1500 LMS patients. Overall, in 1L, PFSR-3m and PFSR-6m were 74% (95% confidence interval [CI] 64-82%) and 58% (95% CI 50-66%), respectively. For 2L+, PFSR-3m was 48% (95% CI 41-54%), and PFSR-6m was 28% (95% CI 22-34%). No difference was observed between R-T and NR-T for first or later lines. Under the alternative that the true benefit amounts to a hazard ratio of 0.65, a PFSR-6m ≥70% can be considered to suggest drug activity in 1L. For 2L+, a PFSR-3m ≥62% or PFSR-6m ≥44% would suggest drug activity. Specific results are also provided for uterine LMS.

CONCLUSIONS

This work provides a new benchmark for designing phase II studies for advanced or metastatic LMS.

Classifying ecosystem stressor interactions: Theory highlights the data limitations of the additive null model and the difficulty in revealing ecological surprises

Understanding how multiple co-occurring environmental stressors combine to affect biodiversity and ecosystem services is an on-going grand challenge for ecology. Currently, progress has been made through accumulating large numbers of smaller-scale empirical studies that are then investigated by meta-analyses to detect general patterns. There is particular interest in detecting, understanding and predicting 'ecological surprises' where stressors interact in a non-additive (e.g. antagonistic or synergistic) manner, but so far few general results have emerged. However, the ability of the statistical tools to recover non-additive interactions in the face of data uncertainty is unstudied, so crucially, we do not know how well the empirical results reflect the true stressor interactions. Here, we investigate the performance of the commonly implemented additive null model. A meta-analysis of a large (545 interactions) empirical dataset for the effects of pairs of stressors on freshwater communities reveals additive interactions dominate individual studies, whereas pooling the data leads to an antagonistic summary interaction class. However, analyses of simulated data from food chain models, where the underlying interactions are known, suggest both sets of results may be due to observation error within the data. Specifically, we show that the additive null model is highly sensitive to observation error, with non-additive interactions being reliably detected at only unrealistically low levels of data uncertainty. Similarly, plausible levels of observation error lead to meta-analyses reporting antagonistic summary interaction classifications even when synergies co-dominate. Therefore, while our empirical results broadly agree with those of previous freshwater meta-analyses, we conclude these patterns may be driven by statistical sampling rather than any ecological mechanisms. Further investigation of candidate null models used to define stressor-pair interactions is essential, and once any artefacts are accounted for, the so-called 'ecological surprises' may be more frequent than was previously assumed.

Dose-response evaluation of urinary cadmium and kidney injury biomarkers in Chinese residents and dietary limit standards

BACKGROUND

Cadmium (Cd) is a common heavy metal that mainly causes renal damage. There is a lack of research on the large-scale and systematic evaluation of the association between urinary Cd (U-Cd) and various effect biomarkers among Chinese residents.

METHODS

Based on the establishment process of dietary Cd limit standards by European Food Safety Authority (EFSA), the dose-response relationships between U-Cd and four biomarkers, β2-microglobulin (β2-MG), N-acetyl-β-glucosidase (NAG), microalbumin (mALB), and retinol binding Protein (RBP) were explored, respectively. Toxicokinetic model was used to derive the dietary Cd exposure limit for Chinese residents after critical U-Cd concentration was calculated.

RESULTS

As the sensitive biomarkers of renal injury, β2-MG and NAG were selected to estimate the 95% confidence interval lower limit of the U-Cd benchmark dose (BMDL5) to be 3.07 and 2.98 μg/g Cr, respectively. Dietary Cd exposure limit was calculated to be 0.28 μg/kg bw/day (16.8 μg/day, based on the body weight of 60 kg), which was lower than the average Chinese Cd exposure (30.6 μg/day) by the China National Nutrient and Health Survey.

CONCLUSION

This study established an overall association between U-Cd and renal injury biomarkers, and explored the Chinese dietary Cd exposure limits, which helps improve Chinese Cd exposure risk assessment and provides a reference basis for formulating reasonable exposure standards.

Why do males emerge before females? Sexual size dimorphism drives sexual bimaturism in insects

Conspecific females and males often follow different development trajectories which leads to sex differences in age at maturity (sexual bimaturism, SBM). Whether SBM is typically selected for per se (direct selection hypothesis) or merely represents a side-effect of other sex-related adaptations (indirect selection hypothesis) is, however, still an open question. Substantial interspecific variation in the direction and degree of SBM, both in invertebrates and vertebrates, calls for multi-species studies to understand the relative importance of its evolutionary drivers. Here we use two complementary approaches to evaluate the evolutionary basis of SBM in insects. For this purpose, we assembled an extensive literature-derived data set of sex-specific development times and body sizes for a taxonomically and ecologically wide range of species. We use these data in a meta-analytic framework to evaluate support for the direct and indirect selection hypotheses. Our results confirm that protandry - males emerging as adults before females - is the prevailing form of SBM in insects. Nevertheless, protandry is not as ubiquitous as often presumed: females emerged before males (= protogyny) in about 36% of the 192 species for which we had data. Moreover, in a considerable proportion of species, the sex difference in the timing of adult emergence was negligible. In search for the evolutionary basis of SBM, we found stronger support for the hypothesis that explains SBM by indirect selection. First, across species, the direction and degree of SBM appeared to be positively associated with the direction and degree of sexual size dimorphism (SSD). This is consistent with the view that SBM is a correlative by-product of evolution towards sexually dimorphic body sizes. Second, within protandrous species, the degree of protandry typically increased with plastic increase in development time, with females prolonging their development more than males in unfavourable conditions. This pattern is in conflict with the direct selection hypothesis, which predicts the degree of protandry to be insensitive to the quality of the juvenile environment. These converging lines of evidence support the idea that, in insects, SBM is generally a by-product of SSD rather than a result of selection on the two sexes to mature at different times. It appears plausible that selective pressures on maturation time per se generally cannot compete with viability- and fecundity-mediated selection on insect body sizes. Nevertheless, exceptions certainly exist: there are undeniable cases of SBM where this trait has evolved in response to direct selection. In such cases, either the advantage of sex difference in maturation time must have been particularly large, or fitness effects of body size have been unusually weak.

Challenges and opportunities for comparative studies of survival rates: An example with male pinnipeds

Survival rates are a central component of life-history strategies of large vertebrate species. However, comparative studies seldom investigate interspecific variation in survival rates with respect to other life-history traits, especially for males. The lack of such studies could be due to the challenges associated with obtaining reliable datasets, incorporating information on the 0-1 probability scale, or dealing with several types of measurement error in life-history traits, which can be a computationally intensive process that is often absent in comparative studies. We present a quantitative approach using a Bayesian phylogenetically controlled regression with the flexibility to incorporate uncertainty in estimated survival rates and quantitative life-history traits while considering genetic similarity among species and uncertainty in relatedness. As with any comparative analysis, our approach makes several assumptions regarding the generalizability and comparability of empirical data from separate studies. Our model is versatile in that it can be applied to any species group of interest and include any life-history traits as covariates. We used an unbiased simulation framework to provide "proof of concept" for our model and applied a slightly richer model to a real data example for pinnipeds. Pinnipeds are an excellent taxonomic group for comparative analysis, but survival rate data are scarce. Our work elucidates the challenges associated with addressing important questions related to broader ecological life-history patterns and how survival-reproduction trade-offs might shape evolutionary histories of extant taxa. Specifically, we underscore the importance of having high-quality estimates of age-specific survival rates and information on other life-history traits that reasonably characterize a species for accurately comparing across species.

Rapid Onset of Intranasal Esketamine in Patients with Treatment Resistant Depression and Major Depression with Suicide Ideation: A Meta-Analysis

Objective

We performed a meta-analysis of randomized double-blinded placebo controlled trials (DB-RCTs) to investigate efficacy and safety of intranasal esketamine in treating major depressive disorder (MDD) including treatment resistant depression (TRD) and major depression with suicide ideation (MDSI).

Methods

Mean change in total scores on Montgomery-Åsberg Depression Rating Scale (MADRS) from baseline to different time-points were our primary outcome measure. Secondary efficacy measures included rate of remission of depression and resolution of suicidality.

Results

Eight DB-RCTs (seven published and one un-published) covering 1,488 patients with MDD were included. Esketamine more significantly improved MADRS total scores than placebo starting from 2-4 hours after the first administration (standardized mean difference, -0.41 [95% CI, -0.58 to -0.25], p < 0.00001), and this superiority maintained until end of double-blinded period (28 days). Sub-group analysis showed that superior antidepressant effects of esketamine over placebo in TRD and MDSI was observed from 2-4 hours, which was maintained until 28 days. Resolution of suicide in MDSI was also greater for esketamine than for placebo at 2-4 hours (OR of 2.04, 95% CIs, 1.37 to 3.05, p = 0.0005), but two groups did not statistically differ at 24 hours and day 28. Total adverse events (AEs), and other common AEs including dissociation, blood pressure increment, nausea, vertigo, dysgeusia, dizziness, and somnolence were more frequent in esketamine than in placebo group.

Conclusion

Esketamine showed rapid antidepressant effects in patients with MDD, including TRD and MDSI. The study also suggested that esketamine might be associated with rapid anti-suicidal effects for patients with MDSI.

COVID-19: Where is the treatment?

Even though the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is related to SARS-CoV and Middle East respiratory syndrome coronavirus (MERS-CoV), identifying effective and safe therapeutic strategies remains challenging. In search of finding effective treatments to eradicate the virus and improve disease symptoms, scientists are exploring possible therapies such as anti-viral, anti-malaria, immune therapy, and hormone treatments. However, the efficacy of these treatments was not validated on either SARS-CoV or MERS-CoV. In this study, we have reviewed synthetic evidence achieved through systematic and meta-analysis of therapeutics specific for SARS-CoV-2 and observed that the use of the above-mentioned therapies had no clinical benefits in coronavirus disease 2019 patients and, conversely, displayed side effects.

Meta-analysis of studies on depression prevalence among diabetes mellitus patients in Africa

Diabetes mellitus is a group of metabolic diseases characterized by hyperglycemia resulting from defects in insulin secretion or insulin action. It can be caused by the consumption of carbohydrate meals or medication side effects. Depression as a comorbid condition in an individual with diabetes is accountable for increased disability, mortality, and significant health problem in patients. As a continent, Africa does not have an overall estimation of depression prevalence among diabetes mellitus patients at a regional level. Consequently, this study's purpose was to use the meta-analysis method to summarize estimates of extant studies that have reported depression prevalence among patients with diabetes mellitus in Africa. The literature search method was executed to classify studies with reported depression prevalence with evidently designed inclusion and exclusion criteria. In total, 20 studies from sundry screened articles were appropriate for ultimate inclusion in the meta-analysis. Since substantial heterogeneity was expected, a random-effects meta-analysis was carried out using the number of cases with a total sample size to estimate the prevalence of diabetes mellitus at a regional level. The residual amount of heterogeneity was found to be high according to the statistics of τ² = 0.06; I² = 99.10%, chi-square = 2184.85, degree of freedom = 19 and P =< 0.001. The pooled depression prevalence was 40% within a 95% confidence interval of 29%–51%. The meta-regression analysis result showed that none of the included moderators contributed to the heterogeneity of studies. The result of effect size estimates against its standard error showed publication bias with a P-value of 0.001. The meta-analysis findings of this study have indicated that depression prevalence in Africa is still high. Reporting on numerous risk factors like socio-demographic characteristics were not possible in this study because of a lack of completeness in the included articles. Consequently, screening diabetes patients for comorbid depression with its associated risk factors is highly recommended.

How can the MHC mediate social odor via the microbiota community? A deep dive into mechanisms

Genes of the major histocompatibility complex (MHC) have long been linked to odor signaling and recently researchers’ attention has focused on MHC structuring of microbial communities and how this may in turn impact odor. However, understanding of the mechanisms through which the MHC could affect the microbiota to produce a chemical signal that is both reliable and strong enough to ensure unambiguous transmission of behaviorally important information remains poor. This is largely because empirical studies are rare, predictions are unclear, and the underlying immunological mechanisms governing MHC–microbiota interactions are often neglected. Here, we review the immunological processes involving MHC class II (MHC-II) that could affect the commensal community. Focusing on immunological and medical research, we provide background knowledge for nonimmunologists by describing key players within the vertebrate immune system relating to MHC-II molecules (which present extracellular-derived peptides, and thus interact with extracellular commensal microbes). We then systematically review the literature investigating MHC–odor–microbiota interactions in animals and identify areas for future research. These insights will help to design studies that are able to explore the role of MHC-II and the microbiota in the behavior of wild populations in their natural environment and consequently propel this research area forward.

Seeds and Seedlings in a Changing World: A Systematic Review and Meta-Analysis from High Altitude and High Latitude Ecosystems

The early life-history stages of plants, such as germination and seedling establishment, depend on favorable environmental conditions. Changes in the environment at high altitude and high latitude regions, as a consequence of climate change, will significantly affect these life stages and may have profound effects on species recruitment and survival. Here, we synthesize the current knowledge of climate change effects on treeline, tundra, and alpine plants’ early life-history stages. We systematically searched the available literature on this subject up until February 2020 and recovered 835 potential articles that matched our search terms. From these, we found 39 studies that matched our selection criteria. We characterized the studies within our review and performed a qualitative and quantitative analysis of the extracted meta-data regarding the climatic effects likely to change in these regions, including projected warming, early snowmelt, changes in precipitation, nutrient availability and their effects on seed maturation, seed dormancy, germination, seedling emergence and seedling establishment. Although the studies showed high variability in their methods and studied species, the qualitative and quantitative analysis of the extracted data allowed us to detect existing patterns and knowledge gaps. For example, warming temperatures seemed to favor all studied life stages except seedling establishment, a decrease in precipitation had a strong negative effect on seed stages and, surprisingly, early snowmelt had a neutral effect on seed dormancy and germination but a positive effect on seedling establishment. For some of the studied life stages, data within the literature were too limited to identify a precise effect. There is still a need for investigations that increase our understanding of the climate change impacts on high altitude and high latitude plants’ reproductive processes, as this is crucial for plant conservation and evidence-based management of these environments. Finally, we make recommendations for further research based on the identified knowledge gaps.

Forest structure, not climate, is the primary driver of functional diversity in northeastern North America

Functional diversity (FD), represented by plant traits, is fundamentally linked to an ecosystem's capacity to respond to environmental change. Yet, little is known about the spatial distribution of FD and its drivers. These knowledge gaps prevent the development of FD-based forest management approaches to increase the trait diversity insurance (i.e., the response diversity) against future environmental fluctuations and disturbances. Our study helps fill these knowledge gaps by (i) mapping the current FD distribution, (ii) and analyzing FD drivers across northeastern North America. Following the stress-dominance hypothesis, we expected a strong environmental filtering effect on FD. Moreover, we expected abundant species to determine the bulk of FD distributions as suggested by the mass-ratio hypothesis. We combined a literature and database review of 44 traits for 43 tree species with terrestrial inventory data of 48,426 plots spanning an environmental gradient from northern boreal to temperate biomes. We evaluated the statistical influence of 25 covariates related to forest structure, climate, topography, soils, and stewardship on FD by employing an ensemble approach consisting of 90 non-parametric models. Temperate forests and the boreal-temperate ecotone east and northeast of the Great Lakes were identified as FD hotspots. Environmental filtering by climate was of secondary importance, with forest structure explaining most of the FD distribution of tree species in northeastern North America. Thus, our study provides only partial support for the stress-dominance hypothesis. Species abundance weightings altered trait diversity distributions and drivers only marginally, supporting the mass-ratio hypothesis. Our results suggest that forest management could increase FD without requiring knowledge of functional ecology by fostering stand structural complexity instead. Further, mixing species from different functional groups identified in this study can enhance the trait diversity insurance of forests to an uncertain future.

Hard-working helpers contribute to long breeder lifespans in cooperative birds

In many species that raise young in cooperative groups, breeders live an exceptionally long time despite high investment in offspring production. How is this possible given the expected trade-off between survival and reproduction? One possibility is that breeders extend their lifespans by outsourcing parental care to non-reproductive group members. Having help lightens breeder workloads and the energy that is saved can be allocated to survival instead. We tested this hypothesis using phylogenetic meta-analysis across 23 cooperatively breeding bird species. We found that breeders with helpers had higher rates of annual survival than those without helpers (8% on average). Increased breeder survival was correlated with reduced investment in feeding offspring, which in turn depended on the proportion of feeding provided by helpers. Helpers had similar effects on female and male breeder survival. Our results indicate that one of the secrets to a long life is reduced investment in parental care. This appears to be a unique feature of cooperative societies with hard-working helpers. This article is part of the theme issue 'Ageing and sociality: why, when and how does sociality change ageing patterns?'

Sediment phosphorus buffering in streams at baseflow: A meta-analysis

Phosphorus (P) pollution of surface waters remains a challenge for protecting and improving water quality. Central to the challenge is understanding what regulates P concentrations in streams. This quantitative review synthesizes the literature on a major control of P concentrations in streams at baseflow-the sediment P buffer-to better understand streamwater-sediment P interactions. We conducted a global meta-analysis of sediment equilibrium phosphate concentrations at net zero sorption (EPC₀ ), which is the dissolved reactive P (DRP) concentration toward which sediments buffer solution DRP. Our analysis of 45 studies and >900 paired observations of DRP and EPC₀ showed that sediments often have potential to remove or release P to the streamwater (83% of observations), meaning that "equilibrium" between sediment and streamwater is rare. This potential for P exchange is moderated by sediment and stream characteristics, including sorption affinity, stream pH, exchangeable P concentration, and particle sizes. The potential for sediments to modify streamwater DRP concentrations is often not realized owing to other factors (e.g., hydrologic interactions). Sediment surface chemistry, hyporheic exchange, and biota can also influence the potential exchange of P between sediments and the streamwater. Methodological choices significantly influenced EPC₀ determination and thus the estimated potential for P exchange; we therefore discuss how to measure and report EPC₀ to best suit research objectives and aid in interstudy comparison. Our results enhance understanding of the sediment P buffer and inform how EPC₀ can be effectively applied to improve management of aquatic P pollution and eutrophication.

Species sensitivities to a global pollutant: A meta-analysis on acoustic signals in response to anthropogenic noise

Anthropogenically driven environmental changes affect our planet at an unprecedented rate. Among these changes are those in the acoustic environment caused by anthropogenic noise, which can affect both animals and humans. In many species, acoustic communication plays a crucial role to maintain social relationships by exchanging information via acoustic signals. However, how species relying on acoustic communication differ in their adjustments to anthropogenic noise is little understood. Yet, this is crucial because protecting species effectively depends on our capability to predict how species differ in their response to human-induced environmental changes. Using a phylogenetically controlled meta-analysis, we quantified differences in adjustments of acoustic signals to anthropogenic noise among species. The effect sizes included in the analysis were obtained from noise exposure experiments, as only carefully controlled experiments allow to establish cause-and-effect relationships. We found that animals changed acoustic signals when exposed to noise, but the magnitude and the direction of adjustments differed among species. Given the importance of communication in the animal kingdom, these adjustments can affect social relationships in many species. The diversity of responses among species highlights the necessity to assess the effect of environmental stressors not only for a few species, because an effect may be positive in one species but negative in another depending on the species' biology. Thus, an effective conservation approach to protect different species is to preserve natural soundscapes of ecosystems to which species have adapted to by reducing or mitigating the emission of anthropogenic noise into the environment.

Tree Diversity and Forest Resistance to Insect Pests: Patterns, Mechanisms, and Prospects

Ecological research conducted over the past five decades has shown that increasing tree species richness at forest stands can improve tree resistance to insect pest damage. However, the commonality of this finding is still under debate. In this review, we provide a quantitative assessment (i.e., a meta-analysis) of tree diversity effects on insect herbivory and discuss plausible mechanisms underlying the observed patterns. We provide recommendations and working hypotheses that can serve to lay the groundwork for research to come. Based on more than 600 study cases, our quantitative review indicates that insect herbivory was, on average, lower in mixed forest stands than in pure stands, but these diversity effects were contingent on herbivore diet breadth and tree species composition. In particular, tree species diversity mainly reduced damage of specialist insect herbivores in mixed stands with phylogenetically distant tree species. Overall, our findings provide essential guidance for forest pest management.

Uncovering patterns of freshwater positive interactions using meta-analysis: Identifying the roles of common participants, invasive species and environmental context

Positive interactions are sensitive to human activities, necessitating synthetic approaches to elucidate broad patterns and predict future changes if these interactions are altered or lost. General understanding of freshwater positive interactions has been far outpaced by knowledge of these important relationships in terrestrial and marine ecosystems. We conducted a global meta-analysis to evaluate the magnitude of positive interactions across freshwater habitats. In 340 studies, we found substantial positive effects, with facilitators increasing beneficiaries by, on average, 81% across all taxa and response variables. Mollusks in particular were commonly studied as both facilitators and beneficiaries. Amphibians were one group benefiting the most from positive interactions, yet few studies investigated amphibians. Invasive facilitators had stronger positive effects on beneficiaries than non-invasive facilitators. We compared positive effects between high- and low-stress conditions and found no difference in the magnitude of benefit in the subset of studies that manipulated stressors. Future areas of research include understudied facilitators and beneficiaries, the stress gradient hypothesis, patterns across space or time and the influence of declining taxa whose elimination would jeopardise fragile positive interaction networks. Freshwater positive interactions occur among a wide range of taxa, influence populations, communities and ecosystem processes and deserve further exploration.

How general is cognitive ability in non-human animals? A meta-analytical and multi-level reanalysis approach

General intelligence has been a topic of high interest for over a century. Traditionally, research on general intelligence was based on principal component analyses and other dimensionality reduction approaches. The advent of high-speed computing has provided alternative statistical tools that have been used to test predictions of human general intelligence. In comparison, research on general intelligence in non-human animals is in its infancy and still relies mostly on factor-analytical procedures. Here, we argue that dimensionality reduction, when incorrectly applied, can lead to spurious results and limit our understanding of ecological and evolutionary causes of variation in animal cognition. Using a meta-analytical approach, we show, based on 555 bivariate correlations, that the average correlation among cognitive abilities is low (r = 0.185; 95% CI: 0.087-0.287), suggesting relatively weak support for general intelligence in animals. We then use a case study with relatedness (genetic) data to demonstrate how analysing traits using mixed models, without dimensionality reduction, provides new insights into the structure of phenotypic variance among cognitive traits, and uncovers genetic associations that would be hidden otherwise. We hope this article will stimulate the use of alternative tools in the study of cognition and its evolution in animals.

Mapping the past, present and future research landscape of paternal effects

BACKGROUND

Although in all sexually reproducing organisms an individual has a mother and a father, non-genetic inheritance has been predominantly studied in mothers. Paternal effects have been far less frequently studied, until recently. In the last 5 years, research on environmentally induced paternal effects has grown rapidly in the number of publications and diversity of topics. Here, we provide an overview of this field using synthesis of evidence (systematic map) and influence (bibliometric analyses).

RESULTS

We find that motivations for studies into paternal effects are diverse. For example, from the ecological and evolutionary perspective, paternal effects are of interest as facilitators of response to environmental change and mediators of extended heredity. Medical researchers track how paternal pre-fertilization exposures to factors, such as diet or trauma, influence offspring health. Toxicologists look at the effects of toxins. We compare how these three research guilds design experiments in relation to objects of their studies: fathers, mothers and offspring. We highlight examples of research gaps, which, in turn, lead to future avenues of research.

CONCLUSIONS

The literature on paternal effects is large and disparate. Our study helps in fostering connections between areas of knowledge that develop in parallel, but which could benefit from the lateral transfer of concepts and methods.

Big City Living: A Global Meta-Analysis Reveals Positive Impact of Urbanization on Body Size in Lizards

Urban environments pose different selective pressures than natural ones, leading to changes in animal behavior, physiology, and morphology. Understanding how animals respond to urbanization could inform the management of urban habitats. Non-avian reptiles have important roles in ecosystems worldwide, yet their responses to urbanization have not been as comprehensively studied as those of mammals and birds. However, unlike mammals and birds, most reptiles cannot easily move away from disturbances, making the selective pressure to adapt to urban environments especially strong. In recent years, there has been a surge in research on the responses of lizards to urbanization, yet no formal synthesis has determined what makes an urban lizard, in other words, which phenotypic traits are most likely to change with urbanization and in which direction? Here, we present a qualitative synthesis of the literature and a quantitative phylogenetic meta-analysis comparing phenotypic traits between urban and non-urban lizard populations. The most robust finding from our analysis is that urban lizards are larger than their non-urban counterparts. This result remained consistent between sexes and taxonomic groups. Hence, lizards that pass through the urban filter have access to better resources, more time for foraging, and/or there is selection on attaining a larger body size. Other results included an increase in the diameters of perches used and longer limb and digit lengths, although this may be a result of increased body size. Urban lizards were not bolder, more active or exploratory, and did not differ in immune responses than non-urban populations. Overall, studies are biased to a few geographic regions and taxa. More than 70% of all data came from three species of anoles in the family Dactyloidae, making it difficult to generalize patterns to other clades. Thus, more studies are needed across multiple taxa and habitats to produce meaningful predictions that could help inform conservation and management of urban ecological communities.

Vitamin D receptor Bsm I polymorphism and osteoporosis risk in postmenopausal women: a meta-analysis from 42 studies

OBJECTIVE

This study aimed to quantitatively summarize the evidence for VDR BsmI gene polymorphism and osteoporosis risk in postmenopausal women.

MATERIALS AND METHODS

The PubMed, EMBASE, Weipu, CNKI, and Wanfang databases were searched for eligible studies. Case-control studies containing available genotype frequencies of B/b were chosen, and odds ratio (OR) with 95% confidence interval (CI) was used to assess the strength of this association.

RESULTS

4485 osteoporosis and 5490 controls were identified in our meta-analysis. In the stratified analysis, a significant association was observed between VDR BsmI gene polymorphism and osteoporosis susceptibility in Caucasians (additive model: OR = 0.809, 95% CI 0.678~0.965, p = 0.019; recessive model: OR = 0.736, 95% CI 0.568~0.955, p = 0.021; and co-dominant model: bb vs. BB OR = 0.701, 95% CI 0.511~0.962 p = 0.028), and we failed to find any significant relationship in Asians.

CONCLUSION

The present meta-analysis suggests that VDR BsmI genotype is associated with increased risk of postmenopausal osteoporosis in Caucasians but not in Asians. To draw comprehensive and true conclusions, further prospective studies with larger numbers of participants worldwide are needed to examine associations between VDR BsmI polymorphism and osteoporosis in postmenopausal women.

Implications of scale dependence for cross-study syntheses of biodiversity differences

Biodiversity studies are sensitive to well-recognised temporal and spatial scale dependencies. Cross-study syntheses may inflate these influences by collating studies that vary widely in the numbers and sizes of sampling plots. Here we evaluate sources of inaccuracy and imprecision in study-level and cross-study estimates of biodiversity differences, caused by within-study grain and sample sizes, biodiversity measure, and choice of effect-size metric. Samples from simulated communities of old-growth and secondary forests demonstrated influences of all these parameters on the accuracy and precision of cross-study effect sizes. In cross-study synthesis by formal meta-analysis, the metric of log response ratio applied to measures of species richness yielded better accuracy than the commonly used Hedges' g metric on species density, which dangerously combined higher precision with persistent bias. Full-data analyses of the raw plot-scale data using multilevel models were also susceptible to scale-dependent bias. We demonstrate the challenge of detecting scale dependence in cross-study synthesis, due to ubiquitous covariation between replication, variance and plot size. We propose solutions for diagnosing and minimising bias. We urge that empirical studies publish raw data to allow evaluation of covariation in cross-study syntheses, and we recommend against using Hedges' g in biodiversity meta-analyses.

Sexual dimorphism in trait variability and its eco-evolutionary and statistical implications

Biomedical and clinical sciences are experiencing a renewed interest in the fact that males and females differ in many anatomic, physiological, and behavioural traits. Sex differences in trait variability, however, are yet to receive similar recognition. In medical science, mammalian females are assumed to have higher trait variability due to estrous cycles (the ‘estrus-mediated variability hypothesis’); historically in biomedical research, females have been excluded for this reason. Contrastingly, evolutionary theory and associated data support the ‘greater male variability hypothesis’. Here, we test these competing hypotheses in 218 traits measured in >26,900 mice, using meta-analysis methods. Neither hypothesis could universally explain patterns in trait variability. Sex bias in variability was trait-dependent. While greater male variability was found in morphological traits, females were much more variable in immunological traits. Sex-specific variability has eco-evolutionary ramifications, including sex-dependent responses to climate change, as well as statistical implications including power analysis considering sex difference in variance.

Males and females differ in appearance, physiology and behavior. But we do not fully understand the health and evolutionary consequences of these differences. One reason for this is that, until recently, females were often excluded from medical studies. This made it difficult to know if a treatment would perform as well in females as males. To correct this, organizations that fund research now require scientists to include both sexes in studies. This has led to some questions about how to account for sex differences in studies.

One reason females have historically been excluded from medical studies is that some scientists assumed that they would have more variable responses to a particular treatment based on their estrous cycles. Other scientists, however, believe that males of a given species might be more variable because of the evolutionary pressures they face in competing for mates. Better understanding how males and females vary would help scientists better design studies to ensure they provide accurate answers.

Now, Zajitschek et al. debunk both the idea that males are more variable and the idea that females are more variable. To do this, Zajitschek et al. analyzed differences in 218 traits, like body size or certain behaviors, among nearly 27,000 male and female mice. This showed that neither male mice nor female mice were universally more different from other mice of their sex across all features. Instead, sex differences in how much variation existed in male or female mice depended on the individual trait. For example, males varied more in physical features like size, while females showed more differences in their immune systems.

The results suggest it is particularly important to consider sex-specific variability in both medical and other types of studies. To help other researchers better design experiments to factor in such variability, Zajitschek et al. created an interactive tool that will allow scientists to look at sex-based differences in individual features among male or female mice.

Does genetic diversity protect host populations from parasites? A meta-analysis across natural and agricultural systems

If parasites transmit more readily between closely related hosts, then parasite burdens should decrease with increased genetic diversity of host populations. This important hypothesis is often accepted at face value—notorious epidemics of crop monocultures testify to the vulnerability of host populations that have been purged of diversity. Yet the relationship between genetic diversity and parasitism likely varies across contexts, differing between crop and noncrop hosts and between experimental and natural host populations. Here, we used a meta‐analytic approach to ask if host diversity confers protection against parasites over the range of contexts in which it has been tested. We synthesized the results of 102 studies, comprising 2004 effect sizes representing a diversity of approaches and host‐parasite systems. Our results validate a protective effect of genetic diversity, while revealing significant variation in its strength across biological and empirical contexts. In experimental host populations, genetic diversity reduces parasitism by ∼20% for noncrop hosts and by ∼50% for crop hosts. In contrast, observational studies of natural host populations show no consistent relationship between genetic diversity and parasitism, with both strong negative and positive correlations reported. This result supports the idea that, if parasites preferentially attack close relatives, the correlation of genetic diversity with parasitism could be positive or negative depending upon the potential for host populations to evolve in response to parasite selection. Taken together, these results reinforce genetic diversity as a priority for both conservation and agriculture and emphasize the challenges inherent to drawing comparisons between controlled experimental populations and dynamic natural populations.

Agricultural diversification promotes multiple ecosystem services without compromising yield

Enhancing biodiversity in cropping systems is suggested to promote ecosystem services, thereby reducing dependency on agronomic inputs while maintaining high crop yields. We assess the impact of several diversification practices in cropping systems on above- and belowground biodiversity and ecosystem services by reviewing 98 meta-analyses and performing a second-order meta-analysis based on 5160 original studies comprising 41,946 comparisons between diversified and simplified practices. Overall, diversification enhances biodiversity, pollination, pest control, nutrient cycling, soil fertility, and water regulation without compromising crop yields. Practices targeting aboveground biodiversity boosted pest control and water regulation, while those targeting belowground biodiversity enhanced nutrient cycling, soil fertility, and water regulation. Most often, diversification practices resulted in win-win support of services and crop yields. Variability in responses and occurrence of trade-offs highlight the context dependency of outcomes. Widespread adoption of diversification practices shows promise to contribute to biodiversity conservation and food security from local to global scales.

No sex differences in adult telomere length across vertebrates: a meta-analysis

In many mammalian species, females live on average longer than males. In humans, women have consistently longer telomeres than men, and this has led to speculation that sex differences in telomere length (TL) could play a role in sex differences in longevity. To address the generality and drivers of patterns of sex differences in TL across vertebrates, we performed meta-analyses across 51 species. We tested two main evolutionary hypotheses proposed to explain sex differences in TL, namely the heterogametic sex disadvantage and the sexual selection hypotheses. We found no support for consistent sex differences in TL between males and females among mammal, bird, fish and reptile species. This absence of sex differences in TL across different classes of vertebrates does not support the heterogametic sex disadvantage hypothesis. Likewise, the absence of any negative effect of sexual size dimorphism on male TL suggests that sexual selection is not likely to mediate the magnitude of sex differences in TL across vertebrates. Finally, the comparative analyses we conducted did not detect any association between sex differences in TL and sex differences in longevity, which does not support the idea that sex differences in TL could explain the observed sex differences in longevity.

Effects of immune challenge on expression of life-history and immune trait expression in sexually reproducing metazoans-a meta-analysis

BACKGROUND

Life-history theory predicts a trade-off between investment into immune defence and other fitness-related traits. Accordingly, individuals are expected to upregulate their immune response when subjected to immune challenge. However, this is predicted to come at the expense of investment into a range of other traits that are costly to maintain, such as growth, reproduction and survival. Currently, it remains unclear whether the magnitude of such costs, and trade-offs involving immune investment and other traits, manifests consistently across species and sexes. To address this, we conducted a meta-analysis to investigate how changes in sex, ontogenetic stage and environmental factors shape phenotypic trait expression following an immune challenge.

RESULTS

We explored the effects of immune challenge on three types of traits across sexually reproducing metazoans: life-history, morphological and proximate immune traits (235 effect sizes, 53 studies, 37 species [21 invertebrates vs. 16 vertebrates]). We report a general negative effect of immune challenge on survival and reproduction, a positive effect on immune trait expression, but no effect on morphology or development time. The negative effects of immune challenge on reproductive traits and survival were larger in females than males. We also report a pronounced effect of the immune treatment agent used (e.g. whether the treatment involved a live pathogen or not) on the host response to immune challenge, and find an effect of mating status on the host response in invertebrates.

CONCLUSION

These results suggest that costs associated with immune deployment following an immune challenge are context-dependent and differ consistently in their magnitude across the sexes of diverse taxonomic lineages. We synthesise and discuss the outcomes in the context of evolutionary theory on sex differences in life-history and highlight the need for future studies to carefully consider the design of experiments aimed at disentangling the costs of immune deployment.

The pervasive and multifaceted influence of biocrusts on water in the world's drylands

The capture and use of water are critically important in drylands, which collectively constitute Earth's largest biome. Drylands will likely experience lower and more unreliable rainfall as climatic conditions change over the next century. Dryland soils support a rich community of microphytic organisms (biocrusts), which are critically important because they regulate the delivery and retention of water. Yet despite their hydrological significance, a global synthesis of their effects on hydrology is lacking. We synthesized 2,997 observations from 109 publications to explore how biocrusts affected five hydrological processes (times to ponding and runoff, early [sorptivity] and final [infiltration] stages of water flow into soil, and the rate or volume of runoff) and two hydrological outcomes (moisture storage, sediment production). We found that increasing biocrust cover reduced the time for water to pond on the surface (-40%) and commence runoff (-33%), and reduced infiltration (-34%) and sediment production (-68%). Greater biocrust cover had no significant effect on sorptivity or runoff rate/amount, but increased moisture storage (+14%). Infiltration declined most (-56%) at fine scales, and moisture storage was greatest (+36%) at large scales. Effects of biocrust type (cyanobacteria, lichen, moss, mixed), soil texture (sand, loam, clay), and climatic zone (arid, semiarid, dry subhumid) were nuanced. Our synthesis provides novel insights into the magnitude, processes, and contexts of biocrust effects in drylands. This information is critical to improve our capacity to manage dwindling dryland water supplies as Earth becomes hotter and drier.

Consequences of multiple imputation of missing standard deviations and sample sizes in meta-analysis

Meta-analyses often encounter studies with incompletely reported variance measures (e.g., standard deviation values) or sample sizes, both needed to conduct weighted meta-analyses. Here, we first present a systematic literature survey on the frequency and treatment of missing data in published ecological meta-analyses showing that the majority of meta-analyses encountered incompletely reported studies. We then simulated meta-analysis data sets to investigate the performance of 14 options to treat or impute missing SDs and/or SSs. Performance was thereby assessed using results from fully informed weighted analyses on (hypothetically) complete data sets. We show that the omission of incompletely reported studies is not a viable solution. Unweighted and sample size-based variance approximation can yield unbiased grand means if effect sizes are independent of their corresponding SDs and SSs. The performance of different imputation methods depends on the structure of the meta-analysis data set, especially in the case of correlated effect sizes and standard deviations or sample sizes. In a best-case scenario, which assumes that SDs and/or SSs are both missing at random and are unrelated to effect sizes, our simulations show that the imputation of up to 90% of missing data still yields grand means and confidence intervals that are similar to those obtained with fully informed weighted analyses. We conclude that multiple imputation of missing variance measures and sample sizes could help overcome the problem of incompletely reported primary studies, not only in the field of ecological meta-analyses. Still, caution must be exercised in consideration of potential correlations and pattern of missingness.

A contrast of meta and metafor packages for meta-analyses in R

There is extensive choice in R to support meta-analyses.Two packages in this ecosystem include meta and metafor and provide an excellent opportunity to apply a structured checklist previously developed for contrasts between R packages relevant to challenges in ecology and evolution.Meta is a direct, intuitive choice for rapid implementation of general meta-analytical statistics. Metafor is a comprehensive package best suited for relatively more complex models.Both packages provide estimates of heterogeneity, excellent visualization tools, and functions to explore publication bias.The package metafor has a steeper learning curve but greater rewards. Reference to the learning curve and capacities of the statistical software Stata provided a benchmark outside the R ecosystem and confirmed the consistency in statistics.The usefulness of meta-analyses is not just in the synthesis of the research but in the process of doing the scientific synthesis. Reporting of contrasts and checks for robust statistics is an important contribution to more transparent and reproducible scientific syntheses.

Effects of antidepressants in the reproduction of aquatic organisms: a meta-analysis

Pharmaceuticals are widespread contaminants across the aquatic systems and despite the role that these compounds play in society today, little is known about their effects in aquatic organisms once they are released into the environment. This study aims to provide quantitative insight on the effects of antidepressants on the reproduction of fish and crustaceans with a multilevel meta-analysis. A systematic literature search identified 19 studies investigating effects of antidepressant exposure in fish or crustaceans' reproduction, according to specific selection criteria. Heterogeneity analysis was performed and the moderating effect of the range of exposure concentrations, exposure time, organism group and toxicant was tested. Additionally, publication bias was also addressed. The results showed that, overall, there is no significant association between antidepressant exposure and the reproduction of fish and crustaceans, however, moderator analysis revealed that the range of concentrations is a significant moderator for fish and crustacean fecundity, showing contrary results between the two groups. Antidepressant concentration had a small, yet positive effect on fish fecundity, meaning that increased concentrations resulted in increased fish fecundity, whilst a negative effect on crustaceans' fecundity was apparent with increasing concentrations. This difference could be related to data artifacts, or, more likely, evidencing a hormetic dose-response curve, with different ranges of exposure concentrations considered in studies on fish and crustaceans. Antidepressants have shown effects on reproductive outcomes in aquatic organisms, based on individual studies and narrative reviews. However, our results show that other factors can have an important role. Additionally, data available for a quantitative assessment is scarce, focusing mainly on a few freshwater species, low concentration ranges and one SSRI compound, fluoxetine. Thus, more research on the subject is needed since meta-analysis are only as statistically powerful as the number of, good quality, studies they include.

Agomelatine for the Treatment of Generalized Anxiety Disorder: A Meta-Analysis

Objective

Despite multiple drugs available, a large proportion of patients with generalized anxiety disorder (GAD) do not show adequate response and remission. Thus, additional novel pharmacological agents are needed to increase treatment option for GAD. We aimed to investigate efficacy and safety of agomelatine in the treatment of GAD by conducting a meta-analysis.

Methods

An extensive search of multiple databases and clinical trial registries were conducted. Mean change in total scores on Hamilton Anxiety Rating Scale (HAM-A) from baseline to endpoint was our primary outcome measure. Secondary efficacy measures included response and remission rates, as defined by a 50% or greater reduction in HAM-A total scores and a score of 7 or less in HAM-A total scores at study endpoint respectively.

Results

Four published double blinded, randomized, placebo-controlled trials were included in this meta-analysis. Agomelatine more significantly (standardized mean difference = −0.56, p = 0.004) improved HAM-A total scores than placebo. The odds ratios (ORs) of agomelatine over placebo for response and remission rates were 3.75 (p < 0.00001) and 2.74 (p < 0.00001), respectively. Agomelatine was generally well tolerated with insignificance in dropout rate, somnolence, headache, nasopharyngitis, and dizziness compared with placebo. However, agomelatine showed significantly higher incidence of liver function increment (OR = 3.13, p = 0.01) and nausea (OR = 3.27, p = 0.02).

Conclusion

We showed that agomelatine may be another treatment option in patients with GAD. However, the results should be interpreted and translated into clinical practice with caution because the meta-analysis was based on limited numbers of clinical trials.

Understory Vegetation Change Following Woodland Reduction Varies by Plant Community Type and Seeding Status: A Region-Wide Assessment of Ecological Benefits and Risks

Woodland encroachment is a global issue linked to diminished ecosystem services, prompting the need for restoration efforts. However, restoration outcomes can be highly variable, making it difficult to interpret the ecological benefits and risks associated with woodland-reduction treatments within semiarid ecosystems. We addressed this uncertainty by assessing the magnitude and direction of vegetation change over a 15-year period at 129 sagebrush (Artemisia spp.) sites following pinyon (Pinus spp.) and juniper (Juniperus spp.) (P-J) reduction. Pretreatment vegetation indicated strong negative relationships between P-J cover and the abundance of understory plants (i.e., perennial grass and sagebrush cover) in most situations and all three components differed significantly among planned treatment types. Thus, to avoid confounding pretreatment vegetation and treatment type, we quantified overall treatment effects and tested whether distinct response patterns would be present among three dominant plant community types that vary in edaphic properties and occur within distinct temperature/precipitation regimes using meta-analysis (effect size = lnRR = ln[posttreatment cover/pretreatment cover]). We also quantified how restoration seedings contributed to overall changes in key understory vegetation components. Meta-analyses indicated that while P-J reduction caused significant positive overall effects on all shrub and herbaceous components (including invasive cheatgrass [Bromus tectorum] and exotic annual forbs), responses were contingent on treatment- and plant community-type combinations. Restoration seedings also had strong positive effects on understory vegetation by augmenting changes in perennial grass and perennial forb components, which similarly varied by plant community type. Collectively, our results identified specific situations where broad-scale efforts to reverse woodland encroachment substantially met short-term management goals of restoring valuable ecosystem services and where P-J reduction disposed certain plant community types to ecological risks, such as increasing the probability of native species displacement and stimulating an annual grass-fire cycle. Resource managers should carefully weigh these benefits and risks and incorporate additional, appropriate treatments and/or conservation measures for the unique preconditions of a given plant community in order to minimize exotic species responses and/or enhance desirable outcomes.