Diet of two commercially important shark species in the United Arab Emirates: milk shark,Rhizoprionodon acutus (Rüppell, 1837), and slit‐eye shark,Loxodon macrorhinus (Müller & Henle, 1839)

The diets of the milk shark, Rhizoprionodon acutus, and the slit‐eye shark, Loxodon macrorhinus, landed from the artisanal fishery in the Arabian Gulf waters of the United Arab Emirates were investigated to determine their dietary preferences. Stomach contents from 57 milk sharks and 53 slit eye sharks were collected from Abu Dhabi (R. acutus, n = 23), Dubai (R. acutus, n = 5; L. macrorhinus, n = 15) and Ras Al Khaimah (R. acutus, n = 29; L. macrorhinus, n = 38) during fishery surveys from January to May 2012. Prey items were identified to the lowest possible taxonomic level, grouped into five categories including ‘teleost fish’, ‘cephalopods’, ‘crustaceans’, ‘invertebrates’, and ‘other’. The diets of both species were described using the numeric, frequency and weight methods, and the index of relative importance (IRI). The majority of stomachs for both species had food, with 66.6% of milk shark stomachs and 90.5% of slit‐eye shark stomachs containing prey items, both dominated by small teleosts. Rhizoprionodon acutus fed on a wide variety of teleost species, primarily Engraulidae (anchovies) (28%), Gerreidae (mojarras) (5.6%) and Carangidae (jacks) (1.6%) with occasional crustacean and cephalopod prey (8%). On the other hand, L. macrorhinus seemed to have a preference for one species in terms of teleosts (anchovies) (35.1%) and fed on a wider variety of crustaceans and cephalopods (22.6%). There was little overlap in the diets of these two species, suggesting that they may either be using different habitats or that in these waters, the milk shark is a generalist species while the slit‐eye is a specialist feeder.     

Anti-arrhythmic effects of cyclopiazonic acid in Langendorff-perfused murine hearts

We investigated the effects of reducing sarcoplasmic reticular (SR) Ca²⁺ stores using the Ca²⁺-ATPase inhibitor cyclopiazonic acid (CPA) in Langendorff-perfused mouse hearts exposed to different pro-arrhythmic agents all known to produce Ca²⁺-mediated arrhythmogenesis. CPA (100 and 150 nM) produced progressive (beginning over 1 min) and significant (P < 0.0001) reductions in peak amplitudes of Ca²⁺ transients evoked by regular stimulation in isolated Fluo-3 loaded myocytes from F/F₀ = 3.2 ± 0.16 (n = 12 cells) to 1.62 ± 0.012 (n = 6 cells) and 1.53 ± 0.06 (n = 12 cells), respectively, consistent with previous reports describing reductions of store Ca²⁺ in other cell systems. The corresponding effects of CPA were then examined in intact hearts exposed to isoproterenol (100 nM), elevated extracellular [Ca²⁺] (5 mM) and caffeine (1 mM). All three agents produced ventricular tachycardia either when added alone or simultaneously with CPA during programmed electrical stimulation. However, arrhythmogenicity was not observed when such agents were added 10 min after introduction of CPA. CPA thus antagonized this Ca²⁺-mediated arrhythmogenesis but only under circumstances of SR Ca²⁺ depletion. These alterations in arrhythmogenic tendency took place despite an absence of alterations in electrogram and monophasic action potential characteristics. This was in sharp contrast to previous observations in murine, ΔKPQ-Scn5a (LQT3) and KCNE1^−/− (LQT5), systems where re-entry has been implicated in arrhythmogenesis.     

Evaluating the link between predation and pest control services in the mite world

1. Pest regulation by natural enemies has a strong potential to reduce the use of synthetic pesticides in agroecosystems. However, the effective role of predation as an ecosystem service remains largely speculative, especially with minute organisms such as mites.
2. Predatory mites are natural enemies for ectoparasites in livestock farms. We tested for an ecosystem level control of the poultry pest Dermanyssus gallinae by other mites naturally present in manure in poultry farms and investigated differences among farming practices (conventional, free‐range, and organic).
3. We used a multiscale approach involving (a) in vitro behavioral predation experiments, (b) arthropod inventories in henhouses with airborne DNA, and (c) a statistical model of covariations in mite abundances comparing farming practices.
4. Behavioral experiments revealed that three mites are prone to feed on D. gallinae. Accordingly, we observed covariations between the pest and these three taxa only, in airborne DNA at the henhouse level, and in mites sampled from manure. In most situations, covariations in abundances were high in magnitude and their sign was positive.
5. Predation on a pest happens naturally in livestock farms due to predatory mites. However, the complex dynamics of mite trophic network prevents the emergence of a consistent assemblage‐level signal of predation. Based on these results, we suggest perspectives for mite‐based pest control and warn against any possible disruption of ignored services through the application of veterinary drugs or pesticides.

     

Kinetic Behavior of Native Alkaline Phosphatase from Human Placenta

The kinetic behavior of human placental alkaline phosphatase, which catalyses the hydrolysis of p-nitrophenyl and of o-carboxyphenyl phosphates, was studied by means of graphical and non-linear regression statistical fitting analysis of data of rate versus substrate concentration. Non linear Lineweaver-Burk and Eadie-Hofstee plots and rational functions of degree 2:2 (F-test assessing the goodness of fit) show non-Michaelian kinetic behavior. In the same way, the behavior of the enzyme was also non-Michaelian in the simultaneous presence of these two substrates.

Norlaudanosoline is a key intermediate in the biosynthesis of the benzylisoquinoline alkaloids providing the benzyl-isoquinoline portion of the morphinan skeleton. This study examines a coupled reaction system for the production of norlaudanosoline from dopamine. In this coupled system, dopamine is enzymatically converted by monoamine oxidase (MAO) to 3,4-dihydroxyphenylacetaldehyde (dopaldehyde). In the presence of dopamine, this aldehyde undergoes a spontaneous Pictet-Spengler condensation to form norlaudanosoline. Three potential sources of MAO were investigated: a fungal source (Aspergillus niger), a bacterial source (Sarcina lutea) and a commercial source isolated from bovine plasma. Kinetic studies with dopamine as the substrate gave Michaelis constants (K_m) of 1.81 × 10^-5 M, 6.94 × 10^-3, and 1.61 × 10^-3 M for A. niger, S. lutea and bovine plasma oxidase, respectively. The reaction system is complicated because of the effect of the condensation reaction, so a more rigorous model was developed to account for this effect. The model was suitable for showing the effect of dopamine concentration on norlaudanosoline production alghough there were some model inadequacies. Using the model a forward rate constant for the Pictet-Spengler condensation was determined to be 6.8 × 10^-2 M^-1 s^-1 and the reverse reaction appears to be negligible. Overall conversion was 14% which is 20 times that achieved in an in situ reaction system using whole cells of Aspergillus niger.