Interactions of sodium,calcium, and lanthanum ions with methyl glycofuranosides in methanol

The ¹³C-n.m.r. spectra have been recorded and assigned for the xylo- and cello-oligosaccharides, the former up to xylopentaose, and the latter up to cello-tetraose. A spectrum of a low-d.p. cellulose in dimethyl sulfoxide-d₆ was also assigned. In every instance, the spectra of the higher oligosaccharides closely parallel those of the corresponding disaccharides. Variations in line intensities permitted assignment of peaks to both terminal groups and internal residues. A particularly important difference was observed between the chemical shifts at the internal C-4 atoms for the two series of oligomers. This difference has been interpreted as evidence for significant differences in average linkage-orientation or solvation, which is related to the absence of C-6 in the xylo-oligosaccharides.     

Metabolic effects of repeated short-term exposures to heat in the rat

Repeated daily exposures of rats to a hot ambient temperature (40-41 degrees C) for 20 days induced activation of the oxidative enzymes in the thigh muscle and of lactate dehydrogenase in the myocardium. Heat-stressed rats also showed increased tolerance to cold. These changes, it is suggested, are caused by the increased sympathetic activity bouts associated with the heat stresses. The interscapular brown adipose tissue, however, showed adaptive changes similar to those induced by warm acclimation. The activity of oxidative enzymes was decreased and the fat droplets became large and unilocular.     

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.