Malgorzata Lagisz

Comparative and meta‐analytic insights into life extension via dietary restriction

Dietary restriction (DR) extends the lifespan of a wide range of species, although the universality of this effect has never been quantitatively examined. Here, we report the first comprehensive comparative meta‐analysis of DR across studies and species. Overall, DR significantly increased lifespan, but this effect is modulated by several factors. In general, DR has less effect in extending lifespan in males and also in non‐model organisms. Surprisingly, the proportion of protein intake was more important for life extension via DR than the degree of caloric restriction. Furthermore, we show that reduction in both age‐dependent and age‐independent mortality rates drives life extension by DR among the well‐studied laboratory model species (yeast, nematode worms, fruit flies and rodents). Our results suggest that convergent adaptation to laboratory conditions better explains the observed DR–longevity relationship than evolutionary conservation although alternative explanations are possible.

Meta-analysis of variation: ecological and evolutionary applications and beyond

Summary 1. Meta-analysis has become a standard way of summarizing empirical studies in many fields, including ecology and evolution. In ecology and evolution, meta-analyses comparing two groups (usually experimental and control groups) have almost exclusively focused on comparing the means, using standardized metrics such as Cohen’s / Hedges’d or the response ratio. 2. However, an experimental treatment may not only affect the mean but also the variance. Investigating differences in the variance between two groups may be informative, especially when a treatment influences the variance in addition to or instead of the mean. 3. In this paper, we propose the effect size statistic lnCVR (the natural logarithm of the ratio between the coefficients of variation, CV, from two groups), which enables us to meta-analytically compare differences between the variability of two groups. We illustrate the use of lnCVR with examples from ecology and evolution. 4. Further, as an alternative approach to the use of lnCVR, we propose the combined use of ln s (the log standard deviation) and ln � (the log mean) in a hierarchical (linear mixed) model. The use of ln s with ln � x overcomes potential limitations of lnCVR and it provides a more flexible, albeit more complex, way to examine variation beyond two-group comparisons. Relevantly, we also refer to the potential use of ln s and lnCV (the log CV) in the context of comparative analysis. 5. Our approaches to compare variability could be applied to already published meta-analytic data sets that compare two-group means to uncover potentially overlooked effects on the variance. Additionally, our approaches should be applied to future meta-analyses, especially when one suspects a treatment has an effect not only on the mean, but also on the variance. Notably, the application of the proposed methods extends beyond the fields of ecology and evolution.

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

Meta-analysis is a statistical procedure for analyzing the combined data from different studies, and can be a major source of concise up-to-date information. The overall conclusions of a meta-analysis, however, depend heavily on the quality of the meta-analytic process, and an appropriate evaluation of the quality of meta-analysis (meta-evaluation) can be challenging. We outline ten questions biologists can ask to critically appraise a meta-analysis. These questions could also act as simple and accessible guidelines for the authors of meta-analyses. We focus on meta-analyses using non-human species, which we term ‘biological’ meta-analysis. Our ten questions are aimed at enabling a biologist to evaluate whether a biological meta-analysis embodies ‘mega-enlightenment’, a ‘mega-mistake’, or something in between.

The effect of resveratrol on longevity across species: a meta-analysis

Resveratrol has shown evidence of decreasing cancer incidence, heart disease, metabolic syndrome and neural degeneration in animal studies. However, the effects on longevity are mixed. We aimed to quantify the current knowledge of life extension from resveratrol. We used meta-analytic techniques to assess the effect resveratrol has on survival, using data from 19 published papers, including six species: yeast, nematodes, mice, fruitflies, Mexican fruitflies and turquoise killifish. Overall, our results indicate that resveratrol acts as a life-extending agent. The effect is most potent in yeast and nematodes, with diminished reliability in most higher-order species. Turquoise killifish were especially sensitive to life-extending effects of resveratrol but showed much variation. Much of the considerable heterogeneity in our analysis was owing to unexplained variation between studies. In summary, we can report that few species conclusively show life extension in response to resveratrol. As such, we question the practice of the substance being marketed as a life-extending health supplement for humans.

Life extension after heat shock exposure: assessing meta-analytic evidence for hormesis.

Hormesis is the response of organisms to a mild stressor resulting in improved health and longevity. Mild heat shocks have been thought to induce hormetic response because they promote increased activity of heat shock proteins (HSPs), which may extend lifespan. Using data from 27 studies on 12 animal species, we performed a comparative meta-analysis to quantify the effect of heat shock exposure on longevity. Contrary to our expectations, heat shock did not measurably increase longevity in the overall meta-analysis, although we observed much heterogeneity among studies. Thus, we explored the relative contributions of different experimental variables (i.e. moderators). Higher temperatures, longer durations of heat shock exposure, increased shock repeat and less time between repeat shocks, all decreased the likelihood of a life-extending effect, as would be expected when a hormetic response crosses the threshold to being a damaging exposure. We conclude that there is limited evidence that mild heat stress is a universal way of promoting longevity at the whole-organism level. Life extension via heat-induced hormesis is likely to be constrained to a narrow parameter window of experimental conditions.

Nonindependence and sensitivity analyses in ecological and evolutionary meta‐analyses

Meta‐analysis is an important tool for synthesizing research on a variety of topics in ecology and evolution, including molecular ecology, but can be susceptible to nonindependence. Nonindependence can affect two major interrelated components of a meta‐analysis: (i) the calculation of effect size statistics and (ii) the estimation of overall meta‐analytic estimates and their uncertainty. While some solutions to nonindependence exist at the statistical analysis stages, there is little advice on what to do when complex analyses are not possible, or when studies with nonindependent experimental designs exist in the data. Here we argue that exploring the effects of procedural decisions in a meta‐analysis (e.g. inclusion of different quality data, choice of effect size) and statistical assumptions (e.g. assuming no phylogenetic covariance) using sensitivity analyses are extremely important in assessing the impact of nonindependence. Sensitivity analyses can provide greater confidence in results and highlight important limitations of empirical work (e.g. impact of study design on overall effects). Despite their importance, sensitivity analyses are seldom applied to problems of nonindependence. To encourage better practice for dealing with nonindependence in meta‐analytic studies, we present accessible examples demonstrating the impact that ignoring nonindependence can have on meta‐analytic estimates. We also provide pragmatic solutions for dealing with nonindependent study designs, and for analysing dependent effect sizes. Additionally, we offer reporting guidelines that will facilitate disclosure of the sources of nonindependence in meta‐analyses, leading to greater transparency and more robust conclusions.

Metabolic rates, and not hormone levels, are a likely mediator of between‐individual differences in behaviour: a meta‐analysis

Summary Consistent individual differences in hormone levels and metabolic rates have been proposed to be potential state variables underlying consistent individual differences in behaviour (i.e. animal personality). However, it remains unclear whether either one alone or both of these potential state variables could be an underlying driver of animal personality. We address this question using meta-analyses of published data from bird species. We hypothesized that state variables that mediate individual differences in behaviour would display similar or higher repeatability estimates than behavioural traits. To test this hypothesis, we quantified repeatability estimates of hormone levels, metabolic rates and behavioural traits. We found moderate to high mean repeatability estimates for both metabolic rates and behavioural traits, but low repeatability estimates for hormone levels. These findings indicate that metabolic rates likely represent an important mechanism for generating adaptive personality differences in behaviour. We also show that: (i) for hormones and behaviour, repeatability decreased with increasing interval time between two measurements; (ii) males and females differed in repeatability for behavioural traits; (iii) stress-induced hormone levels were more repeatable than baseline levels. Future studies are now required to determine the direction of the association between metabolic rates and behavioural traits. At the same time, these studies should try to investigate which of the proposed mechanisms is responsible for the relationship between state variable and state-dependent behaviour. In addition, we encourage researchers to report the coefficient of variation for between-individual variance (CVB) along with repeatability estimates because these two indices carry different information. We discuss how CVB may better facilitate future comparative studies, including meta-analyses. A lay summary is available for this article.

Spatial Dynamic Factors Affecting Population-Level Risk Assessment for a Terrestrial Arthropod: An Agent-Based Modeling Approach

ABSTRACT Agent-based models (ABMs) explicit handling of space and time and integration of nonlinear interactions between system components to create a system response could facilitate realistic risk assessment modeling. We used this approach to evaluate the impact of spatial dynamic factors on a theoretical risk assessment of an insecticide on a carabid beetle population (based on Bembidion lampros). Results indicated that both impacts and recovery were dependent on period of application, area treated, spatial distribution of stressor, beetle dispersal, and underlying habitat suitability. The impact of the stressor was detected far outside the area to which it was applied, and the extent of this impact was affected by beetle dispersal and landscape structure. The results call into question the validity of the recovery endpoint as assessed by field trials because model recovery was primarily influenced by reinvasion, depleting surrounding areas. Despite the simplicity of the acute stressor/Bembidion system modeled, the results obtained were highly variable dependent on the precise inputs used. Therefore, we suggest that application of modeling to risk assessment in the future will require a much more complete description of the risk assessment problem than has hitherto been the case.

The long and the short of avian W chromosomes: no evidence for gradual W shortening.

The well-established view of the evolution of sex chromosome dimorphism is of a gradual genetic and morphological degeneration of the hemizygous chromosome. Yet, no large-scale comparative analysis exists to support this view. Here, we analysed karyotypes of 200 bird species to test whether the supposed directional changes occur in bird sex chromosomes. We found no support for the view that W chromosomes gradually become smaller over evolutionary time. On the contrary, the length of the W chromosome can fluctuate over short time scales, probably involving both shortening and elongation of non-coding regions. Recent discoveries of near-identical palindromes and neo-sex chromosomes in birds may also contribute to the observed variation. Further studies are now needed to investigate how chromosome morphology relates to its gene content, and whether the changes in size were driven by selection.

Does Urbanization Affect Predation of Bird Nests? A Meta-Analysis

Urbanization can affect interspecific interactions such as predator-prey relationships. Several hypotheses have been postulated to predict how predation on bird nests changes along urbanization gradients; some predict increased and others decreased predation pressures in urban compared to rural habitats. Using a formal meta-analytical approach, we carried out a systematic literature review to test whether predation on natural and artificial bird nests increased or decreased with urbanization. We found that the effect was highly heterogeneous among studies, due to contrasting results between studies that used artificial nests and those that used natural nests. For artificial nests, survival rate tended to decrease with increasing urbanization, with higher predation in more urbanized study sites. For natural nests, survival tended to increase with the level of urbanization. The latter finding supports predictions of the ‘urban habitats as predation-safe zones’ and ‘urban nest predator paradox’ hypotheses, but the effect may be confounded by many studies not distinguishing between predation and other sources of mortality. None of the other considered methodological and ecological variables explained the variation in a robust way. The discrepancy between the results of artificial and natural nest studies may be due to differences in experimental design (e.g., cavity nests have been more commonly studied in natural nest studies), intrinsic differences between the two nest types (e.g., lack of parental nest defense in artificial nests), or sampling bias. We conclude that the direction of the relationship between urbanization and nest predation is likely to depend on the methodology of the study. Therefore, results from studies using different methodologies, particularly natural or artificial nests, should be generalized with caution to avoid over-interpretations.