Seasonal variation in the lateral distribution of mayfly nymphs in a boreal river

Seasonal variations in the lateral distribution of mayfly nymphs were investigated in the North Swedish river Vindelälven; a river with large seasonal differences in water level, current velocity and ice conditions, A total of 22 mayfly species about equally divided between summer and winter species were found along a single transect. At low water level in late summer and autumn most species were distributed over the whole transect. In winter the populations occupying the littoral moved into deeper water, so avoiding the ice. Only very small mortalities were detected in the ice. Prior to the spring flood most characteristically still water species moved to the shallow uppermost littoral while lotic species and the burrowing Ephemera vulgata L. did not show the same aggregation near the shore. It is suggested that these lateral movements allow the nymphs to avoid adverse environmental conditions and to exploit food resources over the whole transect.     

Effects of germanium and silicon on bone mineralization

The chemical properties of Ge are similar to Si. This study investigated whether Ge can substitute for, or is antagonistic to, Si in bone formation. Sixty male weanling Sprague-Dawley rats were randomly assigned to treatment groups of 12 and 6 in a 2×4 factorially arranged experiment. The independent variables were, per gram fresh diet, Si (as sodium metasilicate) at 0 or 25 μg and Ge (as sodium germanate) at 0, 5, 30 or 60 μg. Results confirmed that Ge does not enhance Si deprivation and provided evidence that Ge apparently can replace Si in functions that influence bone composition. When Si was lacking in the diet, calcium and magnesium concentrations of the femur were decreased; this was reversed by feeding either Ge and/or Si. Similar effects were found for zinc, sodium, iron, manganese, and potassium of vertebra. There were some responses to Si deprivation that Ge could not reverse: Ge did not increase femur copper, sodium, or phosphorus or decrease molybdenum of vertebra, effects that were eveked by Si supplementation. Additionally, some findings suggested that 60 μg Ge/g diet could be a toxic intake for the rat. On the other hand, some responses induced by Ge indicate that this element may be acting physiologically other than as a substitute for Si. Germanium itself affected bone composition. Germanium supplementation decreased Si and molybdenum in the femur and increased DNA in tibia. Regardless of the amount of Si fed, animals fed 30 μg Ge/g diet had increased tibial DNA compared to animals fed 0 or 60 μg Ge; however, tibial DNA of animals fed 30 μg Ge was not statistically different from those animals fed 5 μg Ge. Thus, Ge may be of nutritional importance.     

Asymmetric competition between distant taxa: poecilid fishes and water striders

Summary Competition for water surface prey between fish (Priapichtus annectens: Poeciliidae) and water striders (Potamobates unidentatus: Gerridae) was studied in the laboratory and in pools in a small tropical stream. Laboratory experiments showed that fish depressed activity and foraging success of water striders. Large fish (4–5 cm) had a greater effect than small fish (2–3 cm). The field experiment showed that competition was highly asymmetric. Presence of fish decreased water strider foraging success while the reverse interaction was insignificant. It is suggested that the higher individual foraging success of the fish, harassment of water striders by fish and the use of an exclusive resource, benthic invertebrates, by the fish, contribute to this pattern. Habitat use differed between the two species. Fish used the deeper parts of stream pools and water striders used the shallower parts of the pools. Asymmetric interference and exploitation competition may force water striders to use shallow edge habitats.     

KDR activation is crucial for VEGF165-mediated Ca2+ mobilization in human umbilical vein endothelial cells

We have prepared apolyclonal mouse antibody directed against the first threeimmunoglobulin-like domains of the kinase insert domain-containingreceptor (KDR) tyrosine kinase. It possesses the ability to inhibitbinding of the 165-amino acid splice variant of vascular endothelialcell growth factor (VEGF₁₆₅) torecombinant KDR in vitro as well as to reduceVEGF₁₆₅ binding to human umbilical vein endothelial cells (HUVEC). These results confirm that the firstthree immunoglobulin-like domains of KDR are involved in VEGF₁₆₅ interactions. The anti-KDRantibody is able to completely blockVEGF₁₆₅-mediated intracellularCa²⁺ mobilization in HUVEC.Therefore, it appears that binding of VEGF₁₆₅ to the fms-like tyrosinekinase (Flt-1) in these cells does not translate into aCa²⁺ response. This is furtherexemplified by the lack of response to placental growth factor (PlGF),an Flt-1-specific ligand. Additionally, PlGF is unable to potentiatethe effects of submaximal concentrations ofVEGF₁₆₅. Surprisingly, theVEGF-PlGF heterodimer was also very inefficient at eliciting aCa²⁺ signaling event in HUVEC. Weconclude that KDR activation is crucial for mobilization ofintracellular Ca²⁺ in HUVEC inresponse to VEGF₁₆₅.