Strategies of zooplanktivory shape the dynamics and diversity of littoral plankton communities : a mesocosm approach

Planktivorous fish can exert strong top-down control on zooplankton communities. By incorporating different feeding strategies, from selective particulate feeding to cruising filter feeding, fish species target distinct prey. In this study, we investigated the effects of two species with different feeding strategies, the three-spined stickleback (Gasterosteus aculeatus (L.)) and roach (Rutilus rutilus (L.)), on a low-diversity brackish water zooplankton community using a 16-day mesocosm experiment. The experiment was conducted on a small-bodied spring zooplankton community in high-nutrient conditions, as well as a large-bodied summer community in low-nutrient conditions. Effects were highly dependent on the initial zooplankton community structure and hence seasonal variation. In a small-bodied community with high predation pressure and no dispersal or migration, the selective particulate-feeding stickleback depleted the zooplankton community and decreased its diversity more radically than the cruising filter-feeding roach. Cladocerans rather than copepods were efficiently removed by predation, and their removal caused altered patterns in rotifer abundance. In a large-bodied summer community with initial high taxonomic and functional diversity, predation pressure was lower and resource availability was high for omnivorous crustaceans preying on other zooplankton. In this community, predation maintained diversity, regardless of predator species. During both experimental periods, predation influenced the competitive relationship between the dominant calanoid copepods, and altered species composition and size structure of the zooplankton community. Changes also occurred to an extent at the level of nontarget prey, such as microzooplankton and rotifers, emphasizing the importance of subtle predation effects. We discuss our results in the context of the adaptive foraging mechanism and relate them to the natural littoral community.Peer reviewe

Preventive strategies and factors associated with surgically treated necrotising enterocolitis in extremely preterm infants: an international unit survey linked with retrospective cohort data analysis

Objectives To compare necrotising enterocolitis (NEC) prevention practices and NEC associated factors between units from eight countries of the International Network for Evaluation of Outcomes of Neonates, and to assess their association with surgical NEC rates.Design Prospective unit-level survey combined with retrospective cohort study.Setting Neonatal intensive care units in Australia/New Zealand, Canada, Finland, Israel, Spain, Sweden, Switzerland and Tuscany (Italy).Patients Extremely preterm infants born between 240 to 286 weeks’ gestation, with birth weightsExposures NEC prevention practices (probiotics, feeding, donor milk) using responses of an on-line pre-piloted questionnaire containing 10 questions and factors associated with NEC in literature (antenatal steroids, c-section, indomethacin treated patent ductus arteriosus and sepsis) using cohort data.Outcome measures Surgical NEC rates and death following NEC using cohort data.Results The survey response rate was 91% (153 units). Both probiotic provision and donor milk availability varied between 0%–100% among networks whereas feeding initiation and advancement rates were similar in most networks. The 9792 infants included in the cohort study to link survey results and cohort outcomes, revealed similar baseline characteristics but considerable differences in factors associated with NEC between networks. 397 (4.1%) neonates underwent NEC surgery, ranging from 2.4%–8.4% between networks. Standardised ratios for surgical NEC were lower for Australia/New Zealand, higher for Spain, and comparable for the remaining six networks.Conclusions The variation in implementation of NEC prevention practices and in factors associated with NEC in literature could not be associated with the variation in surgical NEC incidence. This corroborates the current lack of consensus surrounding the use of preventive strategies for NEC and emphasises the need for research

Preventive strategies and factors associated with surgically treated necrotising enterocolitis in extremely preterm infants: an international unit survey linked with retrospective cohort data analysis

OBJECTIVES To compare necrotising enterocolitis (NEC) prevention practices and NEC associated factors between units from eight countries of the International Network for Evaluation of Outcomes of Neonates, and to assess their association with surgical NEC rates. DESIGN Prospective unit-level survey combined with retrospective cohort study. SETTING Neonatal intensive care units in Australia/New Zealand, Canada, Finland, Israel, Spain, Sweden, Switzerland and Tuscany (Italy). PATIENTS Extremely preterm infants born between 24$^{0}$ to 28$^{6}$ weeks' gestation, with birth weights<1500 g, and admitted between 2014-2015. EXPOSURES NEC prevention practices (probiotics, feeding, donor milk) using responses of an on-line pre-piloted questionnaire containing 10 questions and factors associated with NEC in literature (antenatal steroids, c-section, indomethacin treated patent ductus arteriosus and sepsis) using cohort data. OUTCOME MEASURES Surgical NEC rates and death following NEC using cohort data. RESULTS The survey response rate was 91% (153 units). Both probiotic provision and donor milk availability varied between 0%-100% among networks whereas feeding initiation and advancement rates were similar in most networks. The 9792 infants included in the cohort study to link survey results and cohort outcomes, revealed similar baseline characteristics but considerable differences in factors associated with NEC between networks. 397 (4.1%) neonates underwent NEC surgery, ranging from 2.4%-8.4% between networks. Standardised ratios for surgical NEC were lower for Australia/New Zealand, higher for Spain, and comparable for the remaining six networks. CONCLUSIONS The variation in implementation of NEC prevention practices and in factors associated with NEC in literature could not be associated with the variation in surgical NEC incidence. This corroborates the current lack of consensus surrounding the use of preventive strategies for NEC and emphasises the need for research

HacA-Independent Functions of the ER Stress Sensor IreA Synergize with the Canonical UPR to Influence Virulence Traits in Aspergillus fumigatus

Endoplasmic reticulum (ER) stress is a condition in which the protein folding capacity of the ER becomes overwhelmed by an increased demand for secretion or by exposure to compounds that disrupt ER homeostasis. In yeast and other fungi, the accumulation of unfolded proteins is detected by the ER-transmembrane sensor IreA/Ire1, which responds by cleaving an intron from the downstream cytoplasmic mRNA HacA/Hac1, allowing for the translation of a transcription factor that coordinates a series of adaptive responses that are collectively known as the unfolded protein response (UPR). Here, we examined the contribution of IreA to growth and virulence in the human fungal pathogen Aspergillus fumigatus. Gene expression profiling revealed that A. fumigatus IreA signals predominantly through the canonical IreA-HacA pathway under conditions of severe ER stress. However, in the absence of ER stress IreA controls dual signaling circuits that are both HacA-dependent and HacA-independent. We found that a ΔireA mutant was avirulent in a mouse model of invasive aspergillosis, which contrasts the partial virulence of a ΔhacA mutant, suggesting that IreA contributes to pathogenesis independently of HacA. In support of this conclusion, we found that the ΔireA mutant had more severe defects in the expression of multiple virulence-related traits relative to ΔhacA, including reduced thermotolerance, decreased nutritional versatility, impaired growth under hypoxia, altered cell wall and membrane composition, and increased susceptibility to azole antifungals. In addition, full or partial virulence could be restored to the ΔireA mutant by complementation with either the induced form of the hacA mRNA, hacAi, or an ireA deletion mutant that was incapable of processing the hacA mRNA, ireAΔ10. Together, these findings demonstrate that IreA has both HacA-dependent and HacA-independent functions that contribute to the expression of traits that are essential for virulence in A. fumigatus

Size and carbon and nitrogen contents of <i>P</i>. <i>grani</i> nauplii and the experimental algae.

<p>Size and carbon and nitrogen contents of <i>P</i>. <i>grani</i> nauplii and the experimental algae.</p

Observed and expected relative contribution of the primary and secondary prey in the diet of nauplii as a function of their relative carbon contribution in the bialgal suspension.

<p>(A) <i>Isochrysis galbana</i> in the bialgal suspension composed of <i>Isochrysis galbana</i> and <i>Heterocapsa sp</i>.; (B) <i>Isochrysis galbana</i> in the bialgal suspension composed of <i>Isochrysis galbana</i> and <i>Gymnodinium litoralis</i>. Corrections for <i>Isochrysis</i>-sized particles generated when feeding on the larger prey are also shown (see text). Line is spline fit to the data.</p

Effects of the presence of alternative prey on the functional response of <i>Paracartia grani</i> nauplii on <i>Isochrysis galbana</i>.

<p>(A) Clearance rate as a function of <i>Isochrysis galbana</i> concentration in unialgal suspension and in mixture with <i>Heterocapsa</i> sp. (B) Clearance rate as a function of <i>Isochrysis galbana</i> concentration in unialgal suspension and in mixture with <i>Gymnodinium litoralis</i>. (C) Ingestion rate as a function of <i>Isochrysis galbana</i> concentration in unialgal suspension and in mixture with <i>Heterocapsa</i> sp. (D) Ingestion rate as a function of <i>Isochrysis galbana</i> concentration in unialgal suspension and in mixture with <i>Gymnodinium litoralis</i>. Unialgal data were fit to non-linear equations like in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0172902#pone.0172902.g001" target="_blank">Fig 1</a>. For the bialgal experiments, correction for <i>Isochrysis</i>-sized particles generated when feeding on the larger prey are also shown (see text). Mixed suspension data were fit with linear equations (only shown for the uncorrected values).</p

Feeding rates on the alternative prey in the bialgal experiments.

<p>Feeding rates on the alternative prey in the bialgal experiments.</p

Total (both prey) ingestion rate of <i>Paracartia grani</i> nauplii as a function of total prey concentration in the bialgal experiments.

<p>Total (both prey) ingestion rate of <i>Paracartia grani</i> nauplii as a function of total prey concentration in the bialgal experiments.</p

Prey concentrations in the feeding experiments.

<p>Prey concentrations in the feeding experiments.</p