The duality of stability: towards a stochastic theory of species interactions

Understanding the dynamics of ecological systems using stability concepts has been a key driver in ecological research from the inception of the field. Despite the tremendous effort put into this area, progress has been limited due to the bewildering number of metrics used to describe ecological stability. Here, we seek to resolve some of the confusion by unfolding the dynamics of a simple consumer-resource interaction module. In what follows, we first review common dynamical metrics of stability (CV, eigenvalues). We argue using the classical type II consumer-resource model as an example where the empirical stability metric, CV, hides two different, but important, aspects of stability: (i) stability due to mean population density processes and (ii) stability due to population density variance processes. We then employ a simple stochastic consumer-resource framework in order to elucidate (i) when we expect these two different aspects of stability to arise in ecological systems and, importantly, highlight (ii) the fact that these two different aspects of stability respond differentially, but predictably, to changes in fundamental parameters that govern biomass flux and loss in any consumer-resource interaction (e.g., attack rates, carrying capacity, mortality).     

Fate of aluminium and nickel in soil. Evaluation through lysimeters under laboratory conditions

ABSTRACT

Nanomaterials (Nms) applications and environmental deposition are continuously increasing. Aluminum (Al) and nickel (Ni) fate in soil, both from gamma alumina-based Nms and as chloride salts were evaluted through lysimeters. After 85 days of treatment, which included irrigation and collection of eluates, the soil of each lysimeter was divided into four sections. The metal concentration was analyzed in eluates, soil samples, and extracts. Al and iron (Fe) present in soil eluted from Control lysimeter. Al from Nms suspension treatment was quantified in the eluates since 30 days on. Ni eluted upon solid salt deposition on top of one device. These results indicate that Al and Ni applied under certain conditions on soil, could leach and reach groundwater. The total concentration and bioavailability (extractable metals) of Al and Fe in soils showed similar patterns. Ni was retained only in the soil of devices treated with chloride salts. Bioavailability % results were of concern for Ni under certain conditions of treatment: 15.57% and 11.08% in two chloride salt-treated lysimeters versus 0.55% and 0.47% of those in control and treated with Nms lysimeters. Conducting studies with different kinds of soil and longer treatment periods should be useful to understand Nms-metals fate in the environment. The results presented here constitute important evidences both for significant metal release from Nms and elution and for considerable Ni bioavailability, after deposition on soil in the form of Nms or as a chloride salt, respectively. Then, possible toxic effects could occur through exposure of aquatic and terrestrial organisms.     

Meta-analysis of variation suggests that embracing variability improves both replicability and generalizability in preclinical research

The replicability of research results has been a cause of increasing concern to the scientific community. The long-held belief that experimental standardization begets replicability has also been recently challenged, with the observation that the reduction of variability within studies can lead to idiosyncratic, lab-specific results that cannot be replicated. An alternative approach is to, instead, deliberately introduce heterogeneity, known as “heterogenization” of experimental design. Here, we explore a novel perspective in the heterogenization program in a meta-analysis of variability in observed phenotypic outcomes in both control and experimental animal models of ischemic stroke. First, by quantifying interindividual variability across control groups, we illustrate that the amount of heterogeneity in disease state (infarct volume) differs according to methodological approach, for example, in disease induction methods and disease models. We argue that such methods may improve replicability by creating diverse and representative distribution of baseline disease state in the reference group, against which treatment efficacy is assessed. Second, we illustrate how meta-analysis can be used to simultaneously assess efficacy and stability (i.e., mean effect and among-individual variability). We identify treatments that have efficacy and are generalizable to the population level (i.e., low interindividual variability), as well as those where there is high interindividual variability in response; for these, latter treatments translation to a clinical setting may require nuance. We argue that by embracing rather than seeking to minimize variability in phenotypic outcomes, we can motivate the shift toward heterogenization and improve both the replicability and generalizability of preclinical research.

A meta-analysis study of the variability in phenotypic outcomes in both control and experimental animal models of ischaemic stroke provides novel perspectives in which heterogeneity can be embraced to improve the reproducibility and translation of preclinical studies.     

A unique macrophage subpopulation signals directly to progenitor cells to promote regenerative neurogenesis in the zebrafish spinal cord

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Plasma prolactin levels in maturing intact and cryptorchid male rats: development of stress response.

In order to determine the possible role of the seminiferous tubules in the regulation of prolactin secretion during sexual development, male rats were rendered cryptorchid at 22 days of age, and thereafter different groups of animals were decapitated at 8-10 day intervals between Day 32 and Day 70. Cryptorchid rats showed destruction of the germinal epithelium accompanied by increased plasma FSH and, to a much lesser extent, increased plasma LH titers. Nevertheless, plasma prolactin levels were similar to those of intact controls throughout the entire period studied. Plasma prolactin titers in intact controls remained uniformly low from Day 20 to Day 70, contrasting with previous reports in which increasing prolactin levels have been observed during sexual development. To determine the reason for this apparent discrepancy, a longitudinal experiment was conducted in which intact and cryptorchid male rats were bled every 10 days from Day 30 to Day 70, following a 3-min period of exposure to ether fumes. The prolactin response to this stress increased markedly with age. A similar pattern of prolactin was observed in a cross-sectional study in which different groups of intact animals were bled following a 3-min period of ether exposure, at ages ranging from 20 to 70 daysmthe results indicate that unlike FSH secretion, prolactin secretion is not controlled by the seminiferous tubules. In addition, they suggest that the pattern of increasing plasma prolactin previously described in the developing male rat is at least in part caused by an age-dependent increase in responsiveness of prolactin to stress.