Frequency modulated calls and species recognition in a neotropical frog

Summary The neotropical frogPhysalaemus pustulosus (Leptodactylidae) has a complex advertisement call and different call components perform different functions. The whine is a necessary and sufficient stimulus for species recognition. The chuck provides information about male body size that is used by females in mate choice (Ryan 1980, 1983), but the chuck must be combined with the species-identifying whine to elicit maximum behavioral responses from males and females. One of the important features of the whine in eliciting behavioral responses from both sexes is the direction of frequency modulation. This suggests that current models of species recognition in anurans based on a frequency filtering mechanism of the peripheral auditory system and selective responses to combinations of frequencies in the central nervous system are not sufficient to explain species recognition inP. pustulosus. Recent neurophysiological studies of the anuran torus semicircularis are discussed in terms of a mechanism for decoding frequency sweeps.     

Transference of the high molecular weight carbohydrate sequences of fetuin to the surface of carrot embryo protoplasts

A method is described for the removal of the carbohydrate sequences of glycoproteins, and their covalent attachment to hydrocarbon chains. These synthetic membrane components may then be incorporated into liposome and cell membranes. Pronase-liberated glycopeptides derived from fetuin were linked by a reduced Schiff's base linkage to tetradecyl aldehyde. The resulting glycolipid was incorporated by external addition, into phosphatidylcholine liposomes. Glycolipid transfer to these liposomes rendered them suseptible to agglutination by wheat germ lectin, which binds N-acetylneuraminic acid, the terminal carbohydrate of the high molecular weight fetuin sugar sequence. Sequential removal of the terminal sugars, and subsequent agglutination behaviour towards various lectins, suggests that the carbohydrate sequence had been transfered intact. The glycolipid was incorporated into plant protoplast membranes by incubation with glycolipid-containing liposomes for 2 h at 37°C. These synthetic glycolipids may find a use in the study of carbohydrate-based recognition systems in animal and plant membranes. In addition they may prove useful in the development of cell and membrane tagging and handling techniques, by the insertion of sugar groups not normally present in these membranes.     

Transposition of mobile genetic elements in interspecific hybrids of Drosophila

In situ hybridization of labeled DNA of four mobile dispersed genetic elements (mdg), isolated from D. melanogaster and C. virilis genomes, with polytene chromosomes of the larvae of several Drosophila species has been carried out. The data show that the mdg elements exhibit a high degree of species specificity. The same conclusions are derived from filter hybridization using ³²P-labeled D. melanogaster and D. virilis DNA and cloned mdg sequences immobilized on nitrocellulose filters. We attempted to induce transpositions (jumping) of mdg elements specific for D. virilis chromosomes to the chromosomes of related species (e.g. D. littoralis Meigen) originally lacking the representatives of this family of repeats. For this purpose we produced hybrid stocks with synthetic karyotoypes characterized by different combinations of D. virilis homologous chromosomes and hybrid chromosomes. In one of such stocks we did find by in situ hybridization the insertion of a D. virilis mdg element into the fifth chromosome of D. littoralis Meigen. The transposition (jumping) took place in the only region where somatic pairing between the fifth chromosomes of D. virilis and D. littoralis occurs more or less regularly in the hybrids. Since crossing-over in hybrid chromosomes of males is excluded in such synthetic stocks, gene conversion may be responsible for this transposition. The possible bearing of the phenomenon observed on the problem of hybrid dysgenesis is discussed.     

A New Principle in Polychrome Staining: A System of Automated Staining, Complementary to Hematoxylin and Eosin, and Usable as a Research Tool

A staining system is described in which each stage forms a separate module or unit. All reagents, concentrations of dye, ratios of phosphotungstic acid to dye, pH values, temperature and staining times are standardized and only aqueous solutions used. The technic uses equal strength solutions of orange G, acid fuchsin and methyl (or aniline) blue, in ascending order of molecular size, at pH 2.5 (range: 2.3 to 2.7). Phosphotungstic acid is incorporated in the dyebaths, not used separately, and the combination of this with ferric alum hematoxylin (Lillie's by preference) and either naphthol yellow S or picric acid as a primer, enables fibrin and cytoplasmic components to be demonstrated vividly, with other tissues shown in clear contrasting colors. Erythrocytes are yellow, fibrin red and collagen blue. The system permits substitution of dyes, lending itself to both manual and computer recording and analysis, helped by a notation system for identifying variants. Many of the factors are variable at will. The system aids research into the mechanism of polychrome staining, and, by extrapolation, into the mechanism of action of other stains. Two manually or machine usable progressive polychrome technics intended for routine use are described. They identify tissue components consistently, complementing the standard hematoxylin and eosin stain, and deserve equal attention during reporting. Variants may be used for one-minute one-stage staining of frozen sections, or to give strong colors with 2 mμ acrylic sections.     

Optimized Transection: A Prelude to Oriented Sectioning

A technique is described which permits blocks of tissue to be flat-embedded in euhedral plastic castings and then to be transected along a plane so that sections may be cut which are optimally oriented to the internal ultrastructure of the block. In the transection procedure a hollow plastic cylinder is placed on the specimen trimming block. The cylinder's top prescribes a plane to which the tissue block is accurately oriented and clamped at a predetermined level. Two hand files and a burnisher are worked across the cylinder's top to 1) remove extraneous material above the plane of transection, 2) expose the tissue for sectioning and 3) smooth the block face. The clear plastic at the periphery of the exposed tissue is then easily trimmed away with a razor blade. The result is a block face with a flat, reflective surface which may be quickly aligned to the knife on the ultramicrotome. The effort needed to transect, align and face the block is minimal and 1-micron or semithin sections produced will be precisely parallel to, and at, the plane of transection. Dust produced by the transection procedure is easily eliminated from the work area by use of a small disposable vacuum cleaner. The technique of producing optimally oriented light microscope sections, using the transector, is enhanced by application of solvents to the block face which cause it to develop a temporary low relief, exactly matching the structural detail of sections cut from the block face. Areas of interest can be accurately located and isolated on the block face, using only a hand-held razor blade, so that oriented ultrathin sections of important regions can be routinely cut and examined in the electron microscope.     

The influence of gamma radiation on arachidonic acid release and prostacyclin synthesis

Cultured pulmonary artery endothelial cells produce PGI₂ as their primary prostaglandin. Conditions which inhibit cell division have been shown to accelerate the synthesis of this compound. Exposure of endothelial cells to γ raidation results in an irreversible cessation of growth and enhanced production of PGI₂. The level of PGI₂ measured after radiation exposure exceeds that observed in cultures rendered quiescent by serum reduction. This indicates a role for γ radiation in the elevation of PGI₂ levels which is distinct from its effect on cell division. Result presented indicate that exposure to γ radiation does not, in and of itself, elevate PG levels but capacitates cells for enhanced production when presented with appropriate stimuli. Increased PGI₂ synthesis appears to be a result of an observed increase in arachidonic acid release and an activation of cyclooxygenase.     

In situ measurement of filtering rates of the salp, Thalia democratica, on phytoplankton and bacteria

Salps were gently captured in a perspex chamber by a SCUBA diver,who then injected a suspension of ¹⁴C-labeled phytoplanktonand ³H-labeled bacteria into the chamber. After 0.5 h incubationin situ, filtering rates were estimated from incorporation ofthe two isotopes, and expressed as a function of each salp'ssize. Both bacteria and phytoplankton were grazed by Thalia,the latter at higher rates. Weight-specific grazing rates increasedwith increasing size of salp. Estimated hourly rations rangedfrom 1% of bodily C for small Thalia feeding only on phytoplanktonto 8% of bodily C for large Thalia feeding on all particulateorganic C. The method gave repeatable results for Thalia, butwas unsatisfactory for the pteropod, Cavolinia. ¹Present address: Institute of Marine Resources, A-018, Universityof California, San Diego, Scripps Institution of Oceanography,La Jolla, CA 92093, USA.