Species interactions between estuarine detritivores: inhibition or facilitation?

Native Hawaiian estuarine detritivores; the prawn Macrobrachium grandimanus, and the neritid gastropod Neritina vespertina, were maintained in flow-through microcosms with conditioned leaves from two riparian tree species, Hau (Hibiscus tiliaceus) and guava (Psidium guajava). Their ability to beak down leaf detritus was determined when alone and when they were together. In single-species treatments, N. vespertina processed leaves from both trees at higher rates than M. grandimanus, but in combined treatments, facilitation occurred when the substrate consisted of Hau leaves, and interference occurred when the substrate consisted of guava leaves. From this, we conclude that whether detritivore species are functionally redundant, facilitating or inhibiting in their processing of detritus depends not only on the detritivore species, but also on the species composition of the detritus food source.     

Reproductive biology ofAwaous guamensis, an amphidromous Hawaiian goby

Synopsis Spawning season, size at first reproduction, oocyte maturation, and fecundity ofAwaous guamensis, an amphidromous Hawaiian goby, were studied from June 1989 through May 1991 in the Wainiha River, Kau'ai, Hawai'i. Female fish larger than 73 mm standard length (SL) had mature gonads from August through December in 1989 and 1990. Gonadosomatic index (GSI) values for mature females ranged from 0.2 to 14.5 during the spawning season. Male fish larger than 64 mm SL had elevated GSI values from June 1989 through December 1989 and from August 1990 through December 1990. Mature sperm were found in two male fish collected in January and February. GSI values for mature males ranged from less than 0.01 to 4.0 in the spawning season. Size-frequency distributions of measurements of vitellogenic oocyte diameters and microscopic observations of oocytes indicated this species has group-synchronous oocyte development. Ovarian maturation stages examined over a 29-month period suggest that members of the stock spawned at different times within the spawning season, although mass spawning events have been documented for this species. Estimates of clutch sizes from nests measured in situ were comparable to estimates of potential fecundity from in vitro examination of ovaries, and indicated that female fish deposited an entire clutch during a spawning event. No evidence for multiple spawning by an individual fish in a single season was found. However, microscopic observations of brown bodies in some ovaries suggested that individual fish probably spawn more than once in a lifetime.     

Contact reactions between young colonies of the coral Pocillopora damicornis

 Newly settled larvae (primary polyps) or young colonies of the coral Pocillopora damicornis were brought into contact at various periods after planulation to examine isogeneic and allogeneic responses. While young colonies derived from the same colony always fused, those derived from different colonies showed either fusion, nonfusion, or incompatible fusion. Tissues were continuous in incompatibly fused pairs, but a white zone, without zooxanthellae, was observed at the interface. The skeleton was also continuous but a groove with skeletal spines on both sides was observed under the white zone. Polyps originating near the white zone later disappeared or were partially resorbed. After 2–8 months, several incompatibly fused pairs became separated by a skeletal ridge, or by a narrow zone of skeleton without living tissue. Incompatible fusion appears to be a distinct histoincompatible response which later transforms into nonfusion. The period between planulation and initial contact of colonies did not affect the outcomes of the contact experiments. Accepted: 31 January 1996     

Psychiatry: current perspectives in posttraumatic stress disorders

The Scientific Board of the California Medical Association presents the following inventory of items of progress in psychiatry. Each item, in the judgment of a panel of knowledgeable physicians, has recently become reasonably firmly established, both as to scientific fact and important clinical significance. The items are presented in simple epitome and an authoritative reference, both to the item itself and to the subject as a whole, is generally given for those who may be unfamiliar with a particular item. The purpose is to assist busy practitioners, students, research workers or scholars to stay abreast of these items of progress in psychiatry that have recently achieved a substantial degree of authoritative acceptance, whether in their own field of special interest or another.The items of progress listed below were selected by the Advisory Panel to the Section on Psychiatry of the California Medical Association and the summaries were prepared under its direction.     

Buoyant and potentiometric titrations of synthetic polpeptides. II. Five copolypeptides and two nonionizable homopolypeptides in CsCl solutions.

The buoyant density titrations of five ionizable copolypeptides in concentrated CsCl solutions have been determined. The results are used to formulate models for predicting the buoyant density titration behavior of copolypeptides and proteins using the previously reported homopolypeptide buoyant density titration curves. It was determined for these copolypeptides that the best predictive model must include not only the buoyant densities of the constituent amino acid residues and the relative composition, but also hydration and salt binding. Hydrations determined for the homopolypeptides are used in the copolypeptide predictive model. The hydrations of the neutral homopolypeptides were readily calculable since their buoyant densities are thermodynamically defined in terms of their partial specific volumes and hydrations. For the case of a charged macromolecule, an expression for the buoyant density as a function of the number and nature of the bound ions, its partial specific volume, and its relative hydration has also been available for some time. This heretofore intuitive relationship is now derived from thermodynamic principles and allows calculations of hydrations to charged macromolecules which bind either cations, anions, or both. The potentiometric titrations of three of the five copolypeptides in concentrated CsCl solutions were determined in order to study the effect of residue interaction and solvation effects on their ionization behavior. The potentiometric results are also combined directly with the buoyant density titration results to determine the correlation of the buoyant density with the degree of ionization. As in the cases of poly(Glu) and poly(His), the buoyant density of the copolypeptides changed linearily with the degree of ionization. The buoyant density titrations of two nonionizable homopolypeptides, poly(Gly) and poly(Ala), were determined in concentrated CsCl solutions. The buoyant density was found to increase with increasing pH, despite the fact that side chains do not contain ionizable groups. This is the first evidence from homopolypeptide or copolypeptide data that buoyant density changes can be observed from effects other than side-chain ionizations.     

Stimulation of leukemia inhibitory factor receptor degradation by extracellular signal-regulated kinase

Leukemia inhibitory factor (LIF) signals via the heterodimeric receptor complex comprising the LIF receptor alpha subunit (LIFRalpha) and the common signal transducing subunit for interleukin-6 cytokine receptors, gp130. This study demonstrates that in different cell types, the level of LIFRalpha decreases during treatment with LIF or the closely related cytokine oncostatin M (OSM). Moreover, insulin and epidermal growth factor induce a similar LIFRalpha down-regulation. The regulated loss of LIFRalpha is specific since neither gp130 nor OSM receptor beta shows a comparable change in turnover. LIFRalpha down-regulation correlates with reduced cell responsiveness to LIF. Using protein kinase inhibitors and point mutations in LIFRalpha, we demonstrate that LIFRalpha down-regulation depends on activation of extracellular signal-regulated kinase 1/2 and phosphorylation of the cytoplasmic domain of LIFRalpha at serine 185. This modification appears to promote the endosomal/lysosomal pathway of the LIFRalpha. These results suggest that extracellular signal-regulated kinase-activating factors like OSM and growth factors have the potential to lower specifically LIF responsiveness in vivo by regulating LIFRalpha half-life.     

Receptor subunit-specific action of oncostatin M in hepatic cells and its modulation by leukemia inhibitory factor

The related cytokines, interleukin-6 (IL-6), oncostatin M (OSM), and leukemia inhibitory factor (LIF) direct the formation of specific heteromeric receptor complexes to achieve signaling. Each complex includes the common signal-transducing subunit gp130. OSM and LIF also recruit the signaling competent, but structurally distinct OSMRbeta and LIFRalpha subunits, respectively. To test the hypothesis that the particularly prominent cell regulation by OSM is due to signals contributed by OSMRbeta, we introduced stable expression of human or mouse OSMRbeta in rat hepatoma cells which have endogenous receptors for IL-6 and LIF, but not OSM. Both mouse and human OSM engaged gp130 with their respective OSMRbeta subunits, but only human OSM also acted through LIFR. Signaling by OSMRbeta-containing receptors was characterized by highest activation of STAT5 and ERK, recruitment of the insulin receptor substrate and Jun-N-terminal kinase pathways, and induction of a characteristic pattern of acute phase proteins. Since LIF together with LIFRalpha appear to form a more stable complex with gp130 than OSM with gp130 and OSMRbeta, co-activation of LIFR and OSMR resulted in a predominant LIF-like response. These results suggest that signaling by IL-6 cytokines is not identical, and that a hierarchical order of cytokine receptor action exists in which LIFR ranks as dominant member.