A model for seasonal phytoplankton blooms

We analyse a generic bottom-up nutrient phytoplankton model to help understand the dynamics of seasonally recurring algae blooms. The deterministic model displays a wide spectrum of dynamical behaviours, from simple cyclical blooms which trigger annually, to irregular chaotic blooms in which both the time between outbreaks and their magnitudes are erratic. Unusually, despite the persistent seasonal forcing, it is extremely difficult to generate blooms that are both annually recurring and also chaotic or irregular (i.e. in amplitude) even though this characterizes many real time-series. Instead the model has a tendency to 'skip' with outbreaks often being suppressed from 1 year to the next. This behaviour is studied in detail and we develop analytical expressions to describe the model's flow in phase space, yielding insights into the mechanism of the bloom recurrence. We also discuss how modifications to the equations through the inclusion of appropriate functional forms can generate more realistic dynamics.     

Indole-3-propionic acid, a melatonin-related molecule, protects hepatic microsomal membranes from iron-induced oxidative damage: relevance to cancer reduction

Excessive free iron and the associated oxidative damage are commonly related to carcinogenesis. Among the antioxidants known to protect against iron-induced oxidative abuse and carcinogenesis, melatonin and other indole compounds recently have received considerable attention. Indole-3-propionic acid (IPA), a deamination product of tryptophan, with a structure similar to that of melatonin, is present in biological fluids and is an effective free radical scavenger. The aim of the study was to examine the effect of IPA on experimentally induced oxidative changes in rat hepatic microsomal membranes. Microsomes were preincubated in presence of IPA (10, 3, 2, 1, 0.3, 0.1, 0.01 or 0.001 mM) and, then, incubated with FeCl(3) (0.2 mM), ADP (1.7 mM) and NADPH (0.2 mM) to induce oxidative damage. Alterations in membrane fluidity (the inverse of membrane rigidity) were estimated by fluorescence spectroscopy and lipid peroxidation by measuring concentrations of malondialdehyde+4-hydroxyalkenals (MDA+4-HDA). IPA, when used in concentrations of 10, 3 or 2 mM, increased membrane fluidity, although at these concentrations it did not influence lipid peroxidation significantly. The decrease in membrane fluidity due to Fe(3+) was completely prevented by preincubation in the presence of IPA at concentrations of 10, 3, 2 or 1 mM. The enhanced lipid peroxidation due to Fe(3+) was prevented by IPA only at the highest concentration (10 mM). It is concluded that Fe(3+)-induced rigidity and, to a lesser extent, lipid peroxidation in microsomal membranes may be reduced by IPA. However, IPA in high concentrations increase membrane fluidity. Besides melatonin, IPA may be used as a pharmacological agent to protect against iron-induced oxidative damage to membranes and, potentially, against carcinogenesis.     

Biological indicators in marine and coastal waters: a statistical and modelling analysis of the MARS campaign

We perform a statistical analysis of ecological data collected in the MARS project from marine environments of the Red and Mediterranean Seas in Israel, and the North Sea in Germany. In the study of fish parasite data, we examine the basic premise that the complex host lifecycles of heteroxenous (h) parasites make them more sensitive to pollution than monoxenous (m) parasites which have only one host. Unlike results from analyses of earlier survey data, we find that the pooled h/m index for a community is not a clear indicator of environmental stress as originally hypothesized. This is due to the relatively large seasonal variability at the sampling sites over the course of the 3-year survey. Other possible indicators for water pollution gradients are checked, including species richness, diversity and prevalence of parasite populations. A theoretical model of host-parasite population dynamics that makes the presence of ecological thresholds transparent is offered to help explain the abrupt transitions prominent in the distributions of parasites at different sites under different pollution loadings. Heavy metal and chlorinated hydrocarbon data collected from fish tissue samples and molluscs of the three seas are assessed as bioindicators for pollution monitoring. The xenobiotic loads and indices of defence system activity and tissue damage are shown to have great potential as monitoring bioindicators.     

Fertility assurance through extrapair fertilizations and male paternity defense

Extrapair paternity has been observed in many formally monogamous species. Male pursuit of extrapair fertilizations is explained by the advantages of having offspring that receive essential paternal care from other males. Since females are capable of exercising a degree of control over the post-copulatory sperm competition, extrapair paternity cannot persist unless it confers fitness benefits on cuckolding females. Thus, extrapair paternity involves cooperation between mated females and extrapair males. On the other hand, paired males frequently exhibit strategies that minimize their loss of paternity and/or conserve paternal investment if paternity is lost. Hence, extrapair attributes of diverse species and populations reported in the literature are particular solutions of evolutionary games involving gender-specific cuckolding/anti-cuckolding strategies. Here we use methods of evolutionary game theory to study the role of male paternity guarding strategies in situations where females seek extrapair fertilizations for reasons of genetic compatibility and/or in pursuit of genetic diversity for their offspring. Our results indicate that in these circumstances pursuit of extrapair fertilizations is the only evolutionary stable female strategy. Males, on the other hand, have two, mutually exclusive, evolutionary stable strategies: full time pursuit of extrapair fertilizations and a compromise strategy wherein they protect in-pair paternity during their mate's fertile periods and pursue extrapair paternity the rest of the time. The relative merits of these two strategies are determined by the efficiency of male in-pair paternity defense, breeding synchrony, fitness advantages of extrapair over in-pair offspring, and the intensity of competition for extrapair fertilizations from floater males.     

An evaluation of the value of first thyroglobulin determination in the diagnostics of metastases immediately following differentiated thyroid carcinoma surgery

INTRODUCTION: Evaluation of the differential value of the first thyroglobulin (Tg) concentration, measured after thyroidectomy (Tx) but before thyroid remnant ablation, in patients with differentiated thyroid carcinoma (DTC) as a marker of either metastases or residual cancer (M). MATERIAL AND METHODS: Data from 517 patients with DTC after Tx, with follow-up > 1.5 year were analysed retrospectively. Patients in whom either the course of the disease was unclear or interference in the Tg test was possible (a-TgAb [+], Tg recovery < 80%) were excluded from the study. Finally, the data from 247 patients were evaluated (age: 14-79 years; 223 women, 24 men). The results of TSH, thyroid radioiodine uptake (T(up24)), thyroid remnant volume (V) and Tg in patients with diagnosed M (group M1; n = 35) were compared with the same parameters in patients with remission > 1.5 year (group M0; n = 212). The area under the ROC curve was calculated. The clinical decision limit of Tg level to be suggestive of metastases was determined by means of efficiency curve. RESULTS: Groups M0 and M1 did not differ from each other with respect to TSH concentration (median 49.7 mIU/l vs 44.3; p = 0.16) or thyroid remnant volume (1.4 vs 1.1 ml; p = 0.79). However, they did differ with respect to T(up24) (7.6 vs 3.2%; p = 0.01) and Tg (4.5 vs 96.7 ng/ml; p = 0.000000). Area under ROC for Tg was 0.78 +/- 0.05 (mean +/- s.e.m.). The decision limit of Tg for suspected M was determined at 38.1 ng/ml, Tg sensitivity was 0.57 (95%CI 0.39-0.74) and specificity 0.96 (95%CI 0.92-0.98). CONCLUSIONS: First thyroglobulin concentration, determined after thyroidectomy but before other treatment, is higher in patients with metastatic DTC than in patients without such metastases. This indicates that Tg level may be used as an early marker of either residual or metastatic DTC (even if thyroid remnants are present).     

The potential for using red claw crayfish and hybrid African catfish as biological control agents for Schistosoma host snails

The potential of red claw crayfish and hybrid African catfish (Clarias gariepinus and Clarias ngamensis) as predators for Schistosoma host snails was evaluated in 2014 by monitoring the consumption of snails by crayfish and catfish in experimental tanks over time under laboratory conditions. After 15 days, both crayfish and catfish had significantly reduced the populations of Bulinus globosus. Crayfish consumed 6.9 snails d^?1, whereas catfish consumed 5.9 snails d^?1. However, when supplied with an alternative prey, Melanoides tuberculata (100 individuals per tank), crayfish clearly preferred M. tuberculata (100% consumed over seven days) to B. globosus (100 individuals per tank) (54% consumed over the same period). Catfish, conversely, did not have a clear preference for either prey species, consuming 77% and 88% of M. tuberculata and B. globosus, respectively. It was also observed that young catfish were more efficient predators than older ones, because of ontogenetic shifts in their diet with age. Hybrid catfish retain the molluscivorous characteristics of their parent stock and red claw crayfish also preys on Schistosoma host snails. However, the effectiveness of both predators is affected by the presence of an alternative prey. Therefore, under suitable conditions, these species can be considered for biological control of schistosomiasis transmission.     

Biological Control of Sheep Parasites using Duddingtonia flagrans: Trials on Commercial Farms in Sweden

   

Trials were conducted on 3 commercial sheep farms in Sweden to assess the effect of administering spores of the nematode trapping fungus, Duddingtonia flagrans, together with supplementary feed to lactating ewes for the first 6 weeks from turn-out on pastures in spring. Also control groups of ewes, receiving only feed supplement, were established on all 3 farms. Groups were monitored by intensive parasitological investigation. The ewes and their lambs were moved in late June to saved pastures for summer grazing, the lambs receiving an anthelmintic treatment at this time. After approximately 6 weeks on summer pasture the lambs were weaned, treated a second time with anthelmintic, and returned to their original lambing pastures for finishing. Decisions as to when lambs were to be marketed were entirely at the discretion of the farmer co-operators. No difference in lamb performance was found between the two treatments on all three farms. This was attributed to the high levels of nutrition initially of the ewes limiting their post-partum rise in nematode faecal egg counts in spring, which in turn resulted in low levels of nematode infection on pastures throughout the autumn period. Additionally, pastures were of good quality for the lambs during the finishing period, so they grew at optimal rates as far as the farmers were concerned.     

Carcinogen-Induced, Free Radical-Mediated Reduction in Microsomal Membrane Fluidity: Reversal by Indole-3-propionic Acid

Chromium (Cr) is a well established carcinogen, with Cr(III) accounting for much of the intracellular oxidative damage that this transition metal induces. Indole-3-propionic acid (IPA), a melatonin-related molecule, is a reported antioxidant and free radical scavenger. Concentration (1, 10, 100, 500, or 1000 M) and time (15, 30, 45, 60, or 90 min)-dependent effects of Cr(III) in the presence of H₂O₂ (0.5 mM), as well as the protective effect of IPA on Cr(III)-induced alterations in membrane fluidity (the inverse of membrane rigidity), as an index of membrane damage, were estimated by fluorescence spectroscopy. Cr(III), in a concentration- and a time-dependent manner, decreased membrane fluidity, with marked effects at a concentration of 500 M and 60 min of incubation. IPA (5, 3, or 1 mM) prevented the Cr(III)-induced decrease in membrane fluidity. It is concluded that the carcinogen Cr(III), in the presence of H₂O₂, generates free radicals, which decrease membrane fluidity in rat microsomal membranes. Membrane alterations are pharmacologically prevented by the antioxidant IPA.