Modelling seasonal growth and composition of the kelp Saccharina latissima

A dynamical model for simulating growth of the brown macroalga Saccharina latissima is described. In addition to wet and dry weights, the model simulates carbon and nitrogen reserves, with variable C/N ratio. In effect, the model can be used to emulate seasonal changes in growth and composition of the alga. Simulation results based on published, environmental field data are presented and compared with corresponding data on growth and composition. The model resolves seasonal growth, carbon and nitrogen content well, and may contribute to the understanding of how seasonal growth in S. latissima depends simultaneously on a combination of several environmental factors: light, nutrients, temperature and water motion. The model is applied to aquaculture problems such as estimating the nutrient scavenging potential of S. latissima and estimating the potential of this kelp species as a raw material for bioenergy production.     

Broth Microdilution and Time–Kill Testing of Caspofungin, Voriconazole, Amphotericin B and their Combinations Against Clinical Isolates of Candida krusei

Treatment of invasive Candida krusei infections can be difficult due to its intrinsic fluconazole resistance and its reduced susceptibility to amphotericin B and flucytosine. Caspofungin (CAS) acts on a different cellular target, and its combination with voriconazole (VOR) or amphotericin B (AmB) appears promising. We evaluated the activity of CAS, VOR and AmB alone and in combination at 1/4, 1, 4xMIC concentrations by time–kill method against 30 C. krusei isolates. All isolates were susceptible to CAS and VOR; AmB MICs were 2 μg/ml for 50% of isolates by broth microdilution. CAS showed a fast killing activity at all concentrations; it was fungistatic at 1/4xMICs and fungicidal at 1-4xMICs in general. VOR displayed a concentration-independent fungistatic activity against all isolates. AmB exhibited a concentration-dependent activity; it was fungistatic at 1/4-1xMIC and fungicidal at 4xMIC. The most common interaction was indifference for both combinations. Frequency of synergic interaction for the VOR + CAS combination was 66.7% at 1/4xMIC after 48 h. The best results for CAS + AmB combination were obtained at 4xMIC in the first 4–8 h; synergic interaction was detected for 20 isolates (66.7%) at 4xMIC after 4 h. Consequently, VOR and CAS alone have been found effective, and high AmB MICs are remarkable against clinical C. krusei isolates in vitro. The combinations of CAS with VOR or AmB have exhibited promising results.     

The dynamics of coordinated group hunting and collective information transfer among schooling prey

Predator-prey interactions are vital to the stability of many ecosystems. Yet, few studies have considered how they are mediated due to substantial challenges in quantifying behavior over appropriate temporal and spatial scales. Here, we employ high-resolution sonar imaging to track the motion and interactions among predatory fish and their schooling prey in a natural environment. In particular, we address the relationship between predator attack behavior and the capacity for prey to respond both directly and through collective propagation of changes in velocity by group members. To do so, we investigated a large number of attacks and estimated per capita risk during attack and its relation to the size, shape, and internal structure of prey groups. Predators were found to frequently form coordinated hunting groups, with up to five individuals attacking in line formation. Attacks were associated with increased fragmentation and irregularities in the spatial structure of prey groups, features that inhibit collective information transfer among prey. Prey group fragmentation, likely facilitated by predator line formation, increased (estimated) per capita risk of prey, provided prey schools were maintained below a threshold size of approximately 2 m(2). Our results highlight the importance of collective behavior to the strategies employed by both predators and prey under conditions of considerable informational constraints.     

Endostyle cell recruitment as a frame of reference for development and growth in the Urochordate Oikopleura dioica

In models of growth and life history, and in molecular and cell biology, there is a need for more accurate frames of reference to characterize developmental progression. In Caenorhabditis elegans, complete fate maps of cell lineage provide such a standard of reference. To be more widely applicable, reference frames should be easier to measure while still providing strong predictive capacity. Towards this aim, we have analyzed growth of the endostyle in the appendicularian Oikopleura dioica at the cellular level, and measured its response to temperature and food availability. Specifically, we test the hypothesis that age of a specific developmental stage in O. dioica can be predicted from the number of endostyle cells and temperature. We show that the endostyle grows by recruiting cells from the posterior tip into the lateral arms of the organ in an anterior-posterior orientation and that the rate of increase in lateral arm endostyle cells is temperature-dependent but unresponsive to nutritional intake. Endostyle cells therefore serve as an accurate and easily measured marker to describe developmental progression. Conceptually, such a method of characterizing developmental progression should help bridge life-history events and molecular mechanisms throughout organismal aging, facilitating cross-disciplinary understanding by providing a common experimental framework.     

Ecological Memory of Historical Contamination Influences the Response of Phytoplankton Communities

Ecological memory (EM) recognizes the importance of previous stress encounters in promoting community tolerance and thereby enhances ecosystem stability, provided that gained tolerances are preserved during non-stress periods. Drawing from this concept, we hypothesized that the recruitment of tolerant species can be facilitated by imposing an initial sorting process (conditioning) during the early stages of community assembly, which should result in higher production (biomass development and photosynthetic efficiency) and stable community composition. To test this, phytoplankton resting stages were germinated from lake sediments originating from two catchments that differed in contamination history: one impacted by long-term herbicides and pesticides exposures (historically contaminated lake) from an agricultural catchment compared to a low-impacted one (near-pristine lake) from a forested catchment. Conditioning was achieved by adding an herbicide (Isoproturon, which was commonly used in the catchment of the historically contaminated lake) during germination. Afterward, the communities obtained from germination were exposed to an increasing gradient of Isoproturon. As hypothesized, upon conditioning, the phytoplankton assemblages from the historically contaminated lake were able to rapidly restore photosynthetic efficiency (p?>?0.01) and became structurally (community composition) more resistant to Isoproturon. The communities of the near-pristine lake did not yield these positive effects regardless of conditioning, supporting that EM was a unique attribute of the historically stressed ecosystem. Moreover, assemblages that displayed higher structural resistance concurrently yielded lower biomass, indicating that benefits of EM in increasing structural stability may trade-off with production. Our results clearly indicate that EM can foster ecosystem stability to a recurring stressor.

     

The emotion system promotes diversity and evolvability

Studies on the relationship between the optimal phenotype and its environment have had limited focus on genotype-to-phenotype pathways and their evolutionary consequences. Here, we study how multi-layered trait architecture and its associated constraints prescribe diversity. Using an idealized model of the emotion system in fish, we find that trait architecture yields genetic and phenotypic diversity even in absence of frequency-dependent selection or environmental variation. That is, for a given environment, phenotype frequency distributions are predictable while gene pools are not. The conservation of phenotypic traits among these genetically different populations is due to the multi-layered trait architecture, in which one adaptation at a higher architectural level can be achieved by several different adaptations at a lower level. Our results emphasize the role of convergent evolution and the organismal level of selection. While trait architecture makes individuals more constrained than what has been assumed in optimization theory, the resulting populations are genetically more diverse and adaptable. The emotion system in animals may thus have evolved by natural selection because it simultaneously enhances three important functions, the behavioural robustness of individuals, the evolvability of gene pools and the rate of evolutionary innovation at several architectural levels.     

A Parameter for IL-10 and TGF-? Mediated Regulation of HIV-1 Specific T Cell Activation Provides Novel Information and Relates to Progression Markers

HIV replication is only partially controlled by HIV-specific activated effector T cells in chronic HIV infection and strategies are warranted to improve their efficacy. Chronic T cell activation is generally accompanied by regulation of antigen-specific T cell responses which may impair an effective control of chronic infections. The impact of HIV-induced T cell regulation on individual patients’ disease progression is largely unknown, since classical T cell activation assays reflect net activation with regulation as unknown contributing factor. We here explore a quantitative parameter for antigen-induced cytokine-mediated regulation (R_AC) of HIV-specific effector T cell activation by functional antibody-blockade of IL-10 and transforming growth factor-β. HIV Env- and Gag-specific T cell activation and R_AC were estimated in peripheral blood mononuclear cells from 30 treatment-naïve asymptomatic HIV-infected progressors (CD4 count 472/µl, HIV RNA 37500 copies/ml) stimulated with overlapping peptide panels for 6 days. R_AC was estimated from differences in T cell activation between normal and blocked cultures, and related to annual CD4 loss, immune activation (CD38) and microbial translocation (plasma lipopolysaccharides). R_AC was heterogeneously distributed between individual patients and the two HIV antigens. Notably, R_AC did not correlate to corresponding classical activation. Env R_AC correlated with CD38 and CD4 loss rates (r> = 0.37, p = <0.046) whereas classical Gag activation tended to correlate with HIV RNA (r = −0.35, p = 0.06). 14 patients (47%) with low R_AC’s to both Env and Gag had higher CD8 counts (p = 0.014) and trends towards lower annual CD4 loss (p = 0.056) and later start with antiretroviral treatment (p = 0.07) than the others. In contrast, patients with high R_AC to both Env and Gag (n = 8) had higher annual CD4 loss (p = 0.034) and lower CD8 counts (p = 0.014). R_AC to Env and Gag was not predicted by classical activation parameters and may thus provide additional information on HIV-specific immunity. R_AC and other assessments of regulation deserve further in-depth exploration.