Sexual signals in electric fishes

Electroreceptive bony fishes of Africa (the Mormyriformes) and South America (the Gymnotiformes) detect and communicate with conspecifics by their continuously discharging electric organs. Laboratory studies of members of each group are beginning to reveal the mechanisms of communicating with and finding mates, offering much scope for future studies of the behavioral ecology of electric fishes.     

Evolution in vitro: sequence and phenotype of a mutant RNA resistant to ethidium bromide

Ethidium bromide inhibits the in vitro replication of MDV-1 RNA (a small replicating RNA molecule) by reducing the rate of chain elongation. In a serial transfer experiment, in the presence of ethidium, a mutant RNA was selected that was more resistant to ethidium inhibition than is the wild-type MDV-1 RNA.The complete nucleotide sequence of the mutant RNA was determined and three nucleotides in the mutant sequence were found to be different from those in the wild type. The mixture of mutant and wild-type RNAs present in successive transfers was also sequenced. Each of the three point mutations occurred at a different time. These results show that the mutant RNA did not arise from a pre-existing strand present in the wild-type population, but rather, occurred de novo in the course of the experiment.It is probable that the chemical basis of resistance is the elimination of ethidium binding sites due to the specific alterations in the nucleotide sequence, since the mutant RNA was found to bind less ethidium than the wild-type molecules.     

Purification and characterization of the carrier protein for juvenile hormone from the hemolymph of the tobacco hornworm Manduca sexta Johannson (Lepidoptera: Sphingidae).

The larval hemolymph of the tobacco hornworm, Manduca sexta, contains a carrier protein that binds specifically and with high affinity the juvenile hormone, an important regulator of insect development. This protein serves to transport the hormone and to protect it from the action of degradative enzymes during early larval stages. Using hemolymph from the last larval stage, we have isolated a pure carrier protein using acetone precipitation, gel filtration, ion exchange chromatography, and preparative isoelectric focusing. Gel filtration, polyacrylamide gel electrophoresis in sodium dodecyl sulfate, and equilibrium ultracentrifugation established that the carrier protein is a single chain polypeptide of approximately 28,000 daltons. The amino acid composition is unexceptional, and no evidence for hexosamine has been obtained. An ion exchange filter disc assay method was used to determine the formation of the complex between the carrier protein and isotopically labeled juvenile hormone. With this technique it was shown that each carrier protein binds one hormone molecule with a dissociation constant of 4.4 +/- 0.2 X 10(-7) M at 0 degrees.     

Dissolved oxygen and fish behavior

Synopsis This essay reviews the behavioral responses of fish to reduced levels of dissolved oxygen from the perspective of optimization theory as used in contemporary behavioral ecology. A consideration of oxygen as a resource suggests that net oxygen gain per unit of energy expenditure will be the most useful currency for ecological models of breathing. In the process of oxygen uptake, fish always expend energy on perfusion, usually on ventilation and often on locomotion. These costs, and the risk of predation, will vary with oxygen availability and the type of behavioral response shown. The principal categories of behavioral response to reduced external availability of dissolved oxygen are (1) changes in activity, (2) increased use of air breathing, (3) increased use of aquatic surface respiration, and (4) vertical or horizontal habitat changes. Fish should choose whichever combination of responses minimizes the costs of meeting their oxygen demands. A small number of studies provides qualitative support for this prediction.     

Bdellovibrio and the intestinal flora of vertebrates.

Bdellovibrio strain MS7 force-fed to fish and frogs via an intragastric tube did not become an integral component of the intestinal microflora. Strain MS7 fed to mice in drinking water was not recovered from the intestinal tract of mice. However, in vitro, the organism multiplied in intestinal contents of frogs and mice. Bdellovibrio inoculated into rabbit ileal loops was greatly reduced in number within 24 h. It was concluded that strains MS7 could be considered nonpathogenic to animals, at least when introduced into the digestive tract, and that it is not feasible at the present time to lyse pathogenic, gram-negative bacteria in the alimentary tract with Bdellovibrio.