Predicted warming and browning affect timing and magnitude of plankton phenological events in lakes: a mesocosm study

1. Aquatic ecosystems in Northern Europe are expected to face increases in temperature and water colour (TB) in future. While effects of these factors have been studied separately, it is unknown whether and how a combination of them might affect phenological events and trophic interactions. 2. In a mesocosm study, we combined both factors to create conditions expected to arise during the coming century. We focused on quantifying effects on timing and magnitude of plankton spring phenological events and identifying possible mismatches between resources (phytoplankton) and consumers (zooplankton). 3. We found that the increases in TB had important effects on timing and abundance of different plankton groups. While increased temperature led to an earlier peak in phytoplankton and zooplankton and a change in the relative timing of different zooplankton groups, increased water colour reduced chlorophyll‐a concentrations. 4. Increased TB together benefitted cladocerans and calanoid copepods and led to stronger top‐down control of algae by zooplankton. There was no sign of a mismatch between primary producers and grazers as reported from other studies. 5. Our results point towards an earlier onset of plankton spring growth in shallow lakes in future with a stronger top‐down control of phytoplankton by zooplankton grazers.     

Effects of brown and turbid water on piscivore–prey fish interactions along a visibility gradient

1. Environmental changes such as eutrophication and increasing inputs of humic matter (brownification) may have strong effects on predator–prey interactions in lakes through a reduction in the visual conditions affecting foraging behaviour of visually oriented predators. 2. In this experiment, we studied the effects of visual range (25–200 cm) in combination with optically deteriorating treatments (algae, clay or brown humic water) on predator–prey interactions between pike (Esox lucius) and roach (Rutilus rutilus). We measured effects on reaction distance and strike distance for pike and escape distance for roach, when pike individuals were exposed to free‐swimming roach as well as to roach held in a glass cylinder. 3. We found that reaction distance decreased with decreasing visual range caused by increasing levels of algae, clay or humic matter. The effect of reaction distance was stronger in turbid water (clay, algae) than in the brown water treatment. 4. Strike distance was neither affected by visual range nor by optical treatment, but we found shorter strike distances when pike attacked roach using visual cues only (roach held in a cylinder) compared to when pike could use multiple senses (free‐swimming roach). Escape distance for roach was longer in turbid than in brown water treatments. 5. Changes in environmental drivers, such as eutrophication and brownification, affecting the optical climate should thus have consequences for the strength of predator–prey interactions through changes in piscivore foraging efficiency and prey escape behaviour. This in turn may affect lake ecosystems through higher‐order interactions.     

Detection and discovery of crustacean parasites in blue crabs (Callinectes sapidus) by using 18S rRNA gene-targeted denaturing high-performance liquid chromatography

Recently, we described a novel denaturing high-performance liquid chromatography (DHPLC) approach useful for initial detection and identification of crustacean parasites. Because this approach utilizes general primers targeted to conserved regions of the 18S rRNA gene, a priori genetic sequence information on eukaryotic parasites is not required. This distinction provides a significant advantage over specifically targeted PCR assays that do not allow for the detection of unknown or unsuspected parasites. However, initial field evaluations of the DHPLC assay suggested that because of PCR-biased amplification of dominant host genes it was not possible to detect relatively rare parasite genes in infected crab tissue. Here, we describe the use of a peptide nucleic acid (PNA) PCR hybridization blocking probe in association with DHPLC (PNA-PCR DHPLC) to overcome inherent PCR bias associated with amplification of rare target genes by use of generic primers. This approach was utilized to detect infection of blue crabs (Callinectes sapidus) by the parasitic dinoflagellate Hematodinium sp. Evaluation of 76 crabs caught in Wassaw Sound, GA, indicated a 97% correspondence between detection of the parasite by use of a specific PCR diagnostic assay and that by use of PNA-PCR DHPLC. During these studies, we discovered one crab with an association with a previously undescribed protist symbiont. Phylogenetic analysis of the amplified symbiont 18S rRNA gene indicated that it is most closely related to the free-living kinetoplastid parasite Procryptobia sorokini. To our knowledge, this is the first report of this parasite group in a decapod crab and of this organism exhibiting a presumably parasitic life history.     

Delayed partial liquid ventilation shows no efficacy in the treatment of smoke inhalation injury in swine.

In an earlier neonatal porcine model of smoke inhalation injury (SII), immediate postinjury application of partial liquid ventilation (PLV) had dramatic beneficial effects on lung compliance, oxygenation, and survival over a 24-h period. To explore the efficacy of PLV following SII, we treated animals at 2 and 6 h after SII and followed them for 72 h. Pigs weighing 8-12 kg were sedated and pharmacologically paralyzed, given a SII, and placed on volume-cycled, pressure-limited ventilation. Animals were randomized to three groups: group I (+SII, no PLV, n = 8), group II (+SII, PLV at 2 h, n = 6), and group III (+SII, PLV at 6 h, n = 7). Ventilatory parameters and arterial blood gasses were obtained at scheduled intervals. The PLV animals (groups II and III) followed a worse course than group I (no PLV); PLV groups had higher peak and mean airway pressures, oxygenation index, and rate-pressure product (a barotrauma index) and lower lung compliance and arterial partial pressure of oxygen-to-inspired oxygen fraction ratio (all P < 0.05). PLV conferred no survival advantage. The reported beneficial effects of PLV with other models of acute lung injury do not appear to extend to the treatment of SII when PLV is instituted in a delayed manner. This study was not able to validate the previously reported beneficial effects of PLV in SII and actually found deleterious effects, perhaps reflecting the predominance of airway over alveolar disease in SII.     

Protein phosphatase 4 is involved in tumor necrosis factor-alpha-induced activation of c-Jun N-terminal kinase.

Protein phosphatase 4 (PP4, previously named protein phosphatase X (PPX)), a PP2A-related serine/threonine phosphatase, has been shown to be involved in essential cellular processes, such as microtubule growth and nuclear factor kappa B activation. We provide evidence that PP4 is involved in tumor necrosis factor (TNF)-alpha signaling in human embryonic kidney 293T (HEK293T) cells. Treatment of HEK293T cells with TNF-alpha resulted in time-dependent activation of endogenous PP4, peaking at 10 min, as well as increased serine and threonine phosphorylation of PP4. We also found that PP4 is involved in relaying the TNF-alpha signal to c-Jun N-terminal kinase (JNK) as indicated by the ability of PP4-RL, a dominant-negative PP4 mutant, to block TNF-alpha-induced JNK activation. Moreover, the response of JNK to TNF-alpha was inhibited in HEK293 cells stably expressing PP4-RL in comparison to parental HEK293 cells. The involvement of PP4 in JNK signaling was further demonstrated by the specific activation of JNK, but not p38 and ERK2, by PP4 in transient transfection assays. However, no direct PP4-JNK interaction was detected, suggesting that PP4 exerts its positive regulatory effect on JNK in an indirect manner. Taken together, these data indicate that PP4 is a signaling component of the JNK cascade and involved in relaying the TNF-alpha signal to the JNK pathway.     

Ultrastructure of Deoxyribonucleic Acid-Membrane Associations in Escherichia coli

Areas of contact between deoxyribonucleic acid (DNA) and intracytoplasmic membrane are frequently seen in the “extra” membrane-forming strain Escherichia coli 0111a₁. By examination of serial sections, it has been estimated that these DNA-membrane associations occur in at least 60% of the extra membrane-containing cells. Most of the DNA masses contained only one contact area. Several cells in which the DNA had been stretched revealed individual fibers connecting to the membrane, suggesting a firm attachment of DNA to membrane. The areas of membrane associated with DNA fibers were usually between 100 and 500 nm in diameter, although some smaller areas were seen. Electron microscopic autoradiography of cells in which the replication forks were labeled showed grains over 24% of the profiles containing a contact area, whereas there were grains over only 16% of the profiles without a contact area. Data from autoradiographs of cells in which the label was “chased” away from the replication fork showed the reverse labeling pattern. These data indicate that the areas of contact between DNA and intracytoplasmic membranes seen in electron micrographs contain the DNA replication forks.