Differences in courtship aggression among six clones of unisexual fish

Hybridization between the viviparous fishes Poeciliopsis monacha and P. lucida of northwestern Mexico has resulted in the formation of diploid and triploid all-female ‘species’, P. monacha-lucida and P. monacha-2 lucida. These females reproduce by mating back to P. lucida, and are essentially clonally reproducing sexual parasites superimposed on that species. In a series of behavioural experiments, one diploid clone proved to be significantly more aggressive than one triploid and four other diploid clones. No differences in aggression were exhibited among the other five clones. The aggressiveness of this one clone may explain why only two clones live in the small tributary where it is found but up to 10 diploid and triploid clones occur where it is absent.     

The partial stream sampling assumption in intestinal perfusion studies

During the past several years, the technique ofin vivo intestinal perfusion with partial stream sampling has been increasingly widely used to gather information on intestinal absorptive processes in man. The basic technique involves infusion of test solution through a proximal opening; and aspiration of samples through one or more distal openings a fixed distance apart. Samples are analyzed for test solute concentrations; from such sample data, conclusions are drawn concerning alterations in stream concentrations between the sampling sites. An underlying assumption for the validity of such a method is: that sample concentrations are the same as average stream concentrations. This assumption has not previously been precisely stated. A precise statement of it is given here, together with an analytic proof of conditions necessary and sufficient for its validity. A brief verbal comment is included to clarify the practical meaning of the analytic statement.     

Changes in stereospecific distribution of yeast fatty acids with age

Stereospecific analyses of glycerolipids from 7-, 14- and 21-day-old cultures of the yeast Lipomyces lipoferus revealed that each position of the glycerolipids had a unique distribution of fatty acids which changed to varying degrees with age, and that, in the triacylglycerols, age had a greater effect on fatty acid content at sn-3 that at sn-1 or sn-2. Age-related changes in unsaturation were, however, greater in the phospholipids than in the triacylglycerols. Among the major phospholipids of L. lipoferus (phosphatidylcholine, phosphatidylinositol and phosphatidylethanolamine), changes in the proportion of unsaturated to saturated fatty acids, and in the number of double bonds per mole, were greater at sn-2 than at sn-1, except for phosphatidylinositol between 14 and 21 days of age. The pattern of acylation of phosphatidylinositol between 14 and 21 days was thus different from that of phosphatidylcholine and phosphatidylethanolamine. Furthermore, at the three ages investigated, phosphatidylinositol had low and relatively constant levels of unsaturation compared with phosphatidylcholine and phosphatidylethanolamine. The net decrease in phospholipid double bonds per mole in aging cells of L. lipoferus, and previous data, suggest that aging in this yeast is accompanied by a decrease in membrane fluidity.     

Conformation of the metastasis-inhibiting laminin pentapeptide

The binding of cancer cells to the basement membrane glycoprotein laminin appears to be a critical step in the metastatic process. This binding can be inhibited competitively by a specific pentapeptide sequence (Tyr-Ile-Gly-Ser-Arg) of the laminin B1 chain, and this peptide can prevent metastasis formationin vivo. However, other similar pentapeptide sequences (e.g., Tyr-Ile-Gly-Ser-Glu) have been found to be much less active in metastasis inhibition, raising the possibility that such amino acid substitutions produce structural changes responsible for altering binding to the laminin receptor. In this study, conformational energy analysis has been used to determine the three-dimensional structures of these peptides. The results indicate that the substitution of Glu for the terminal Arg produces a significant conformational change in the peptide backbone at the middle Gly residue. These results have important implications for the design of drugs that may be useful in preventing metastasis formation and tumor spread.     

Diel methane emission patterns from Scirpus lacustris and Phragmites australis

In mature Phragmites australis and Scirpus lacustris vegetated sediment methane was emitted almost exclusively by plant-mediated transport, whereas in unvegetated, but otherwise identical sediment, methane was emitted almost exclusively by ebullition. Diel variations in methane emission, with highest emission rates at daytime and emission peaks following sunrise, were demonstrated for Phragmites and Scirpus. The diel difference and magnitude of the emission peaks were much smaller for Scirpus than for Phragmites. In contrast to Phragmites, methane concentrations within Scirpus stems did not change significantly over the diel period. These patterns are consistent with a two-way transport mechanism for Phragmites (convective at daytime and diffusive at night-time) and an all day diffusive mechanism for Scirpus. The patterns could not be accounted for by diel variation in air and sediment temperature, plant transpiration, or photosynthetically coupled methane production. Comparison of the experimentally derived ratio of methane emission in helium and nitrogen under light and dark conditions with the theoretical derived ratio (calculated according to the kinetic theory of gases) confirmed the exploitation of the different transport mechanism for Phragmites and Scirpus. Methane emission from Phragmites correlated significantly with incident light, which probably drove the pressure differential associated with thermally induced convection. Decrease of the radial resistance of Scirpus stems for methane transport under light compared to dark conditions, in combination with morphological characteristics of the plant species, suggested that stomatal aperture, regulated by light, controls methane emission from Scirpus. Diel variation in bubble emission from the non-vegetated sediment coincided with sediment temperature changes. The results have important implications for sampling and scaling strategies for estimating methane emission from wetlands.     

Tonnacypris glacialis (Ostracoda, Cyprididae): taxonomic position, (palaeo-) ecology, and zoogeography

Abstract. The freshwater ostracod Tonnacypris glacialis (Sars, 1890) is reported from the European Pleistocene for the first time. The historical allocation of the species is discussed, and the species composition and characteristics of Tonnacypris Diebel & Pietrzeniuk (1975) and its phylozoogeography are considered. The significance of T. glacialis is reviewed, particularly from the viewpoint of the possible implications of parthenogenesis (and occasional-male production) for the Quaternary history of the genus, and for the use of the species in palaeoenvironmental reconstruction. It is suggested that the Pleistocene fossil occurrence of T. glacialis in modern temperature latitudes is a robust indicator of mean summer temperatures of 6°C.     

Filamentous bacteriophage contract into hollow spherical particles upon exposure to a chloroform-water interface

The bacteriophage M13 is a 1 μm long filament consisting of a circular single-stranded DNA loop firmly held within a tubular protein capsid. We report here that exposure to a chloroform-water interface initiates a 20 fold contraction of each filament into a hollow protein sphere. In these 0.04 μm diameter particles, termed M13 “spheroids,” two thirds of the DNA is apparently extruded through a hole in the wall of the spheroid; the portion of DNA remaining inside the shell centers about the origins of M13 DNA replication. These results suggest that the filament, upon exposure to a membrane environment, undergoes an ordered change whereby the DNA is released into the cell and the coat protein is changed to a form more easily solubilized by the membrane lipids.