Type-3 functional response in limnetic suspension-feeders,as demonstrated by in situ grazing rates

Field-measured grazing rates (ml/animal/d) of cladocerans (mostly daphniids) and diaptomids were assembled from various published studies and plotted as a function of corresponding phytoplankton concentration (μg l⁻¹ f.w.). Filtering rates of both zooplankton groups initially increased with seston concentration until maximal grazing rates were observed at approximately 4 × 10² and 1 × 10² μg l⁻¹ for cladocerans and copepods, respectively; at higher algal concentrations, filtering rates of both declined as a function of food concentration. The shape of these curves are most consistent with Holling's (1966) Type 3 functional response. We found little support for the Type 3 functional response in published laboratory studies of Daphnia; most investigators report either a Type 1 or Type 2 response. The one study in which the Type 3 response was observed involved experiments where animals were acclimated at low food concentrations for 24 h, whereas those studies associated with response Types 1 or 2 had acclimation periods of only 1 to 3 h. We therefore assembled relevant data from the literature to examine the effect of acclimation period on the feeding rates of Daphnia at low food concentrations. In the absence of any acclimation, animals filtered at extremely low rates. After 2 h of acclimation, however, filtering rates increased 4 to 5-fold but declined again with longer durations; after > 70 h of pre-conditioning, filtering rates were almost as low as they had been with no acclimation. We also found little support for the Type 3 functional response in published studies of copepods. The only study associated with a Type 3 response involved a marine copepod that had been subjected to a starvation period of 48 h; however, an analysis of the effects of acclimation period did not yield conclusive evidence that filtering rates of freshwater copepods (Diaptomus and Eudiaptomus) decrease significantly with acclimation duration. The low filtering rates associated with long acclimation periods in laboratory experiments appears to be a direct result of animals becoming emaciated from prolonged exposure to low food concentrations, a situation which renders them incapable of high filtering rates. This may explain the Type 3 functional response for field cladocerans, since zooplankton in food-limiting situations are constantly exposed to low food concentrations, and would therefore have low body carbon and consequently less energy to filter-feed. We cannot, however, use this to explain the Type 3 response for field diaptomids, since copepods in the laboratory did not appear to lose body carbon even after 72 h of feeding at very low food levels, and there was inconclusive evidence that either Diaptomus or Eudiaptomus decrease their filtering rates with acclimation period. Although Incipient Limiting Concentrations (ILC) for Daphnia ranged from 1 to 8.5 × 10³ μg 1⁻¹, more than half of these fell between 1 and 3 × 10³ μg l⁻¹, bracketing the value of 2.7 × 10² μg l⁻¹ for field cladocerans. There was, however, a great deal of variation in reported maximum ingestion rates (MIR), maximum filtering rates (MFR) and ILC values for Daphnia magna. ILC values from the few laboratory studies of freshwater copepods ranged between 0.5 to 2.8 × 10³ μg 1⁻¹, and was higher than the ILC value of approximately 0.2 × 10³ μg l⁻¹ calculated for field populations of D. minutus. Generally, there was considerable agreement among laboratory studies regarding the shape of grazing-rate and ingestion-rate curves when data were converted to similar units and presented on standardized scales.     

Accumulation of the labdane diterpene Marrubiin in glandular trichome cells along the ontogeny of Marrubium vulgare plants

The content of the diterpene Marrubiin was assessed by GC-FID in leaves of Marrubium vulgare plants along their ontogeny. Maximum accumulation occurred just before flowering time and in fully expanded leaves. After feeding the plants with radio labeled [³H]-geranyl geranyl diphosphate, up to 70% of the radioactivity was recovered in HPLC-Rt coincidental with authentic Marrubiin, which was also characterized by GC-EIMS, thus confirming that the biosynthesis of Marrubiin proceeds through the 1-deoxy-D-xylulose-5-phosphate pathway. The major accumulation of radioactivity occurred in glandular trichome cells, and the product remained stable throughout.     

Physiographic and climatic events in the Chihuahuan Desert lead to the speciation and distinct demographic patterns of two sister Sceloporus lizards

The biogeographic history of the Chihuahuan Desert is known to be complex, and there is evidence of the effects of physiographic and climatic events in species diversification and demographic population changes in many taxa. Here, using DNA sequence data, we studied the influence of the physiographic and climatic events that occurred in the Chihuahuan Desert during the Pliocene–Pleistocene transition on the speciation and evolutionary history of the sister lizard species Sceloporus cyanostictus and S. gadsdeni. First, based on mtDNA and nDNA sequences, we estimated the divergence times of the sister species. Then, based on mtDNA sequences, we investigated the demographic history of both species within a phylogeographic framework. The divergence time was inferred to be 1.48 Mya, date that corresponds to the existence of a large lake in the Mapimian subprovince, between the current geographic locations of S. cyanostictus and S. gadsdeni. This lake could have acted as a barrier, leading to the speciation of both species. For the demographic history of the two species, we identified two distinct patterns: the population expansion of S. gadsdeni within the Last Glacial Maximum and the potential population decline of S. cyanostictus. Our results can be used as a guide for the study of other aspects that could be critical to developing conservation actions that ensure the survival of not only S. gadsdeni and S. cyanostictus, but also other co‐occurring lizard species.     

Function of minor polypeptides in foot-and-mouth disease virus and poliovirus

Foot-and-mouth disease virus and poliovirus each contain several minor polypeptides, in addition to the four structural proteins. One of these, the viral RNA polymerase, can also act as a nuclease, hydrolysing the RNA and thus destroying viral infectivity. It is tightly bound to the RNA and may be the packaging signal for assembly of the particle.     

Conversion of human interferon-β from a secreted to a phosphatidylinositol anchored protein by fusion of a 17 amino acid sequence to its carboxyl terminus

A number of cell-surface proteins are anchored in plasma membranes by a glycosylated phosphatidylinositol (PI) moiety that is covalently attached to the carboxyl-terminal amino acid of the mature protein. We have previously reported the construction of a cDNA clone of a truncated Platelet-derived growth factor (PDGF) receptor that consists of the extracellular domain without the transmembrane and cytoplasmic domains. In the construction of the vector, a sequence of 51 base pairs (bp) from the 3′-untranslated region of the receptor cDNA was linked in frame with the external domain coding sequence. The truncated receptor protein with the peptide VTSGHCHEERVDRHDGE fused to its carboxyl terminus was covalently attached to the membrane by a PI linkage and it was released by phosphatidylinositol specific-phospholipase C (PI-PLC). When the 51 bp sequence was deleted, the external domain receptor protein was secreted into the media. To determine whether the PI linkage of the protein was due to the 17 amino acids added, the peptide was fused to the carboxyl terminus of the secreted protein human Interferon-β (hu-IFN-β). Chinese hamster ovary (CHO) cells transfected with the hu-IFN-β cDNA secreted the protein to theconditioned media, whereas CHO cells transfected with the carboxyl terminus modified-hu-IFN-β cDNA did not secrete detectable levels of protein. CHO cells expressing the carboxyl terminus modified-hu-IFN-β were treated with PI-PLC, the media and cell lysates were analyzed by SDS-PAGE after immunoprecipitation with antibodies against hu-IFN-β. The modified protein is anchored to the plasma membrane by a PI linkage and it is specifically released by PI-PLC, whereas a control preparation of CHO cells expressing wild type hu-IFN-β does not show the same pattern. The 17 amino acid peptide fused to the carboxyl terminus of IFN-β directs attachment of a PI anchor and targets the fusion protein to the plasma membrane.     

Sickness and Healing: An Anthropological Perspective

Sickness and Healing: An Anthropological Perspective. Robert A. Hahn. New Haven, CT: Yale University Press, 1995 (cloth and paper), viii. 327 pp.     

Oviductosome-Sperm Membrane Interaction in Cargo Delivery: DETECTION OF FUSION AND UNDERLYING MOLECULAR PLAYERS USING THREE-DIMENSIONAL SUPER-RESOLUTION STRUCTURED ILLUMINATION MICROSCOPY (SR-SIM)*

Oviductosomes ((OVS), exosomes/microvesicles), which deliver the Ca²⁺ efflux pump, plasma membrane Ca²⁺ATPase 4 (PMCA4), to sperm are likely to play an important role in sperm fertilizing ability (Al-Dossary, A. A., Strehler, E. E., and Martin-DeLeon, P. A. (2013) PloS one 8, e80181). It is unknown how exosomes/microvesicles deliver transmembrane proteins such as PMCA4 to sperm. Here we define a novel experimental approach for the assessment of the interaction of OVS with sperm at a nanoscale level, using a lipophilic dye (FM4–64FX) and three-dimensional SR/SIM, which has an 8-fold increase in volumetric resolution, compared with conventional confocal microscopy. Coincubation assays detected fusion of prelabeled OVS with sperm, primarily over the head and midpiece. Immunofluorescence revealed oviductosomal delivery of PMCA4a to WT and Pmca4 KO sperm, and also endogenous PMCA4a on the inner acrosomal membrane. Fusion was confirmed by transmission immunoelectron microscopy, showing immunogold particles in OVS, and fusion stalks on sperm membrane. Immunofluorescence colocalized OVS with the αv integrin subunit which, along with CD9, resides primarily on the sperm head and midpiece. In capacitated and acrosome reacted sperm, fusion was significantly (p < 0.001) inhibited by blocking integrin/ligand interactions via antibodies, exogenous ligands (vitronectin and fibronectin), and their RGD recognition motif. Our results provide evidence that receptor/ligand interactions, involving αvβ3 and α5β1integrins on sperm and OVS, facilitate fusion of OVS in the delivery of transmembrane proteins to sperm. The mechanism uncovered is likely to be also involved in cargo delivery of prostasomes, epididymosomes, and uterosomes.