Regime shifts in exploited marine food webs: detecting mechanisms underlying alternative stable states using size-structured community dynamics theory

Many marine ecosystems have undergone ‘regime shifts’, i.e. abrupt reorganizations across trophic levels. Establishing whether these constitute shifts between alternative stable states is of key importance for the prospects of ecosystem recovery and for management. We show how mechanisms underlying alternative stable states caused by predator–prey interactions can be revealed in field data, using analyses guided by theory on size-structured community dynamics. This is done by combining data on individual performance (such as growth and fecundity) with information on population size and prey availability. We use Atlantic cod (Gadus morhua) and their prey in the Baltic Sea as an example to discuss and distinguish two types of mechanisms, ‘cultivation-depensation’ and ‘overcompensation’, that can cause alternative stable states preventing the recovery of overexploited piscivorous fish populations. Importantly, the type of mechanism can be inferred already from changes in the predators'' body growth in different life stages. Our approach can thus be readily applied to monitored stocks of piscivorous fish species, for which this information often can be assembled. Using this tool can help resolve the causes of catastrophic collapses in marine predatory–prey systems and guide fisheries managers on how to successfully restore collapsed piscivorous fish stocks.     

Structure and Conformation of the Branch Core Triribonucleotide Containing 2′-5′ and 3′-5′ Phosphodiester Linkages (A2′p5′G 3′p5′C) in Solution,Essential for Yeast mRNA Splicing,Deduced from 1H-NMR

Abstract

The non-exchangeable ¹H-NMR signals of the branch core trinucleotide of the lariat branch site (A^2′p5′G _3′p5′C), 1) and its derivatives 2 and 3 are completely assigned using one- and two- dimensional NMR techniques including NOE, COSY, NOESY, ¹H-¹HINADEQUATE and 2D-J-resolved spectroscopy. From the vicinal coupling constants in the individual ribose rings, NOE data and T₁ measurements, the following properties of the trimers are deduced.(i)The unique stacking behavior of the trimers is S^1′N _3′N, and the sugar rings exist predominantly in the N-conformation (3′-endo-2′-exo).(ii)The sugar-base orientations appear to be anti.(iii) The branched trimers exist in solution as single-stranded right-handed conformations resembling A-RNA with stacking between the adenine and guanine residues in aqueous solution at 21°C and pH 7.2.(iv) The calculated values for the torsion angles ε^t andγ⁺ for the trimers are 201–203° and 71–86%, respectively, while the percent β¹ values are higher for the guanine (87–92%) than the cytosine residues (73–77%). The computer generated depiction of the triribonucleotide 1 is also shown. These subtle structural features may act as recognition signals for this critical lariat branch site which is essential for the second step in yeast mRNA splicing.     

Influence of ATP and ADP on dissociation of the V-ATPase into its V(1) and V(O) complexes

Although the reversible dissociation of the V(1)V(O) holoenzyme into its V(1) and V(O) complexes is a general mechanism for the regulation of V-ATPases, important aspects are still not understood. By analyzing the endogenous nucleotide content of the V(1)V(O) holoenzyme and of the V(1) complex, both purified from Manduca sexta larval midgut, we found that the V(1) complex contained 1.7 molec. of ADP, whereas only 0.3 molec. of ADP were bound to the V(1)V(O) holoenzyme. By contrast, both proteins contained only negligible amounts of ATP. Incubation of the V(1)V(O) holoenzyme with various adenine nucleotides revealed that ATP hydrolysis, leading to a state containing tightly bound ADP is necessary for its dissociation.     

Development of a Transcreener kinase assay for protein kinase A and demonstration of concordance of data with a filter-binding assay format

A Transcreener kinase fluorescence polarization (FP) assay has been developed for the serine/threonine kinase protein kinase A (PKA). The PKA Transcreener kinase assay is an homogenous, competitive antibody-based FP assay that uses Far Red Alexa Fluor 633-labeled adenosine 5' disphosphate (ADP) tracer and mouse monoclonal anti-ADP antibody. The Transcreener PKA assay was validated with both known PKA inhibitors and library compounds. The Transcreener PKA assay is resistant to low-wavelength (or common) fluorescent interference from small-molecule library compounds and generates IC50 results comparable with current radioactive filter-binding assay.     

Facilitation of fisheries by natural predators depends on life history of shared prey

Predators commonly share prey with human exploiters, intuitively suggesting that there is an inherent human–predator conflict through competition for prey. Here we studied the effects of fishing and predation mortality on biomass distributions and yields of shared prey using a size‐structured model of competing populations, describing the life histories of Baltic Sea sprat and herring. Whereas both species responded in a similar fashion to increased fishing mortality, with decreasing juvenile and adult biomasses, we found that responses to predation mortality differed between species. Sprat only display weak compensatory responses with increasing predation mortality, while over a substantial range of mortalities there was a strong increase in adult (and total) herring biomass, i.e. overcompensation. The observed biomass overcompensation results from relaxed intraspecific competition as predation mortality increased, allowing for faster individual growth rates that in turn lead to a change in population composition (juvenile:adult biomass ratio). Our results suggest that the potential for biomass overcompensation is higher for species exhibiting substantial growth after maturation. Differences in size‐selectivity of predators and fishing mortality resulted in a positive effect of predation mortality on fisheries yields, which can be explained by an overcompensatory response in adult herring biomass. Thus, somewhat counter intuitive, our results suggest that fishermen, depending on prey life history, may actually benefit from allowing for a higher abundance of predators, despite competing for shared prey.     

Soluplus-Solubilized Citrated Camptothecin—A Potential Drug Delivery Strategy in Colon Cancer

Camptothecin (CPT), a potent antitumor drug, exhibits poor aqueous solubility and rapid conversion from the pharmacologically active lactone form to inactive carboxylate form at physiological pH. Solid dispersion of CPT in Soluplus®, an amphiphilic polymeric solubilizer, was prepared to increase the aqueous solubility of CPT and the resultant solid dispersion along with citric acid was formulated as hard gelatin capsules that were subsequently coated with Eudragit S100 polymer for colonic delivery. FTIR spectrum of the solid dispersion confirmed the presence of CPT. PXRD and DSC revealed the semicrystalline nature of solid dispersion. The solubility of the drug was found to increase ~40 times in the presence of Soluplus and ~75 times in solid dispersion. The capsules showed no drug release in 0.01 N HCl but released 86.4% drug in lactone form in phosphate buffer (pH 7.4) and the result appears to be due to citric acid-induced lowering of pH of buffer from 7.4 to 6.0. Thus the presence of citric acid in the formulation led to stabilization of the drug in its pharmacologically active lactone form. Cytotoxicity studies conducted with the formulation of solid dispersion with citric acid, utilizing cell cytotoxicity test (MTT test) on Caco-2 cells, confirmed cytotoxic nature of the formulation.     

Quiescence of CD34-negative haematopoietic stem cells is mediated by downregulation of Cyclin B and no stat activation

The CD34-negative, adherent growing, fibroblast-like canine haematopoietic stem cell line D064 was recently identified as the earliest progenitor population in the bone marrow. D064 cells are predominately quiescent. Quiescence is mediated by the accumulation of the cyclin-dependent kinase inhibitor p27(kip-1)and in parallel, by the downregulation of Cyclin B, leading to an accumulation of quiescent cells in the G(0)/G(1)-phase of the cell cycle. Stem cell factor (SCF), the ligand for the tyrosine kinase receptor c-kit, usually induces differentiation of the CD34-negative stem cells into CD34-positive haematopoietic precursors. SCF also suppresses the expression of c-myc-dependent Cyclin E, which is not transcribed initially, but expression occurs later on. Interleukin 6 (IL-6) instead rather promotes proliferation, but fails to induce proliferation in the majority of CD34-negative stem cells due to no STAT activation in quiescent cells. Nevertheless, the potential of quiescent D064 cells to proliferate eventually, becomes apparent by the low-level expression of IL-6 dependent STAT factors. D064 cells also spontaneously start to express Bax, while Bcl-2 is downregulated in parallel. In summary, CD34-negative haematopoietic stem cells dwell in the marrow or other niches as quiescent cells, until they can respond to autocrine or paracrine growth factor-mediated signals.     

Sequential colonization by river periphyton analysed by microscopy and molecular fingerprinting

1. An artificial glass substratum was incubated in the River Danube for a period of 28 days in order to detect the sequential colonization of microorganisms.
2. Light and fluorescent microscopy showed that microalgae and the picoalgal fraction on the slides increased rapidly over the first 2 weeks of colonization. Diatoms were numerically the most abundant component of the periphyton and their species richness and diversity increased rapidly in the early phase of colonization whereas diversity subsequently increased moderately.
3. Evenness of the diatom community was initially high, lower in the intermediate phase and again higher later on. Succession involving early, intermediate and late colonizer species was observed. Community composition during the first 5 days of colonization was very different from later stages whereas there were only minor changes subsequently.
4. Molecular community analysis by means of terminal restriction fragment length polymorphism analysis of PCR amplified 16S rRNA and 18S rRNA genes pointed to even larger differences between the composition of samples obtained early and late in the period.
5. The number of 18S rRNA and 16S rRNA terminal restriction fragments (T-RF-s) was variable over the colonization period and the fragment patterns of both the bacterial and eukaryotic portion of the microbial community were variable, with most T-RF-s unique to a single sample, suggesting a wide diversity and dynamic properties of periphytic organisms.