Effects of eel (Anguilla anguilla L.) removals from selected sites of a stream on its subsequent densities

We assessed the effect of eel (Anguilla anguilla) removal from three sites of a Cantabrian stream upon its subsequent densities. In the first sample (Sept. 1986) numbers and densities were estimated as 43, 45 and 84 ind and 3490, 3030 and 3750 ind ha ⁻¹. Removal of these eels reduced the subsequent numbers and densities which, except on two occasions, were never reached again during the two years (eleven estimates) of study. Highest densities were recorded in the uppermost site in May and July, 1987, coincident with a strong drought and the lowest densities occurred in 1988 during a normal wet year. We hypothesize first that, because of a selective underground homing behaviour of eels, electro-fishing is inefficient and results in underestimates of the population. Second, seasonal variations of water discharge and droughts may not influence the homing behaviour of'eels until a threshold of dryness is reached. If this occurs, eels abandon their refuges and move towards the stream bottom. It seems that in Arroyo Chabatchos this threshold was exceeded in the summer of 1987 when the highest densities were estimated. The re-colonization of these sites experimentally depleted of eels, is a slow procces that lasts for, at least, two years.     

Phenotypic variations in re-lysogenization ofBacillus licheniformis with temperate phage

A bacitracin-producing strainBacillus licheniformis ATCC 10716 harbors two types of inducible phages (LP52 and DLP 10716). 156 strains re-lysogenized with phage LP52 were independently isolated from a cured strain UM12 ofB. licheniformis. Those strains were divided into 12 groups based on colony morphology and pigment production. Some of the re-lysogenized strains grew faster than UM12 and others produced more bacitracin than the cured strain. For example, the production of bacitracin by one of the relysogenized strains, L89, was enhanced by about 70% in comparison with UM12. The phenotypic variations observed with re-lysogenized strains might be due to the re-insertion of the phage genome at different sites of the chromosome in addition to the pleiotropic effect assumed.Abbreviations ATCC American Type Culture Collection - DNA Deoxyribonucleic acid - MC Mitomycin C - OD Optical density - PFU Plaque forming unit - rpm Revolutions per minute - UOD Unit of optical density - UV Ultraviolet Definition Specific growth rate (h^-1) - t time (h) - X cell concentration (g/l)     

Intra- and intraspecific variation of Juniperus virginiana and J. scopulorum seedling based on volatile oil composition

Comparisons of volatile oil constituents were made among samples of juvenile foliage collected from 78 Juniperus virginiana and 28 J. scopulorum seedling sources growing in a “common garden” environment. A canonical variate analysis, a principal coordinates analysis and hybrid distance diagrams of 30 chemical characters indicate both taxa are good species and that they exhibit clinical patterns in the Great Plains. In addition, a possible evoluitonary link between present-day J. virginiana populations in southern Texas and ancient J. scopulorum populations is indicated.     

Dissolved and suspended mercury. species in the Wabigoon River (Ontario,Canada): seasonal and regional variations

Seasonal and regional variations in the speciation, sediment-water partitioning, and dynamics of mercury (Hg) were studied at selected sites along the Hg-polluted Wabigoon River, and at unpolluted headwater and tributary sites, during April–September, 1979. ‘Dissolved’ and ‘particulate’ forms of Hg in the water were separated by continuous-flow centrifugation in the field. The Hg and other pollutants such as wood chips and salt had been discharged from a chlor-alkali plant and paper mill at Dryden, Ontario. Concentrations and loadings of particulate methyl mercury (CH₃Hg⁺) and total particulate Hg (and loadings of total ‘dissolved’ Hg) were greatest during the spring flood (April-May) owing to accelerated resuspension and transport of sediments. Concentrations of ‘dissolved’ CH₃Hg⁺, however, were highest in the summer (July–September), probably reflecting stimulation of microbial methylating activity by elevated temperatures, together with factors such as reduced levels of metal-scavenging particulates and minimal dilution by runoff. Total dissolved Hg concentrations were relatively high in September at polluted sites only, possibly because of desorption from sediments due to elevated concentrations of Cl⁻ ions. Loadings of dissolved CH₃Hg⁺ tended to be high in the summer but were generally depressed (suggesting sorption by suspended particles) during the major spring-flood episode in May. During July–August dissolved CH₃Hg⁺ was a function of total dissolved Hg, suggesting rapid biomethylation of desorbed inorganic Hg; but in general dissolved and suspended CH₃Hg⁺ levels depended on environmental variables and were unrelated to total Hg concentrations. In the summer only, total dissolved Hg was a function of dissolved Cl⁻. Hg species in particulates were associated with sulfides, hydrated Fe and Mn oxides, organic matter (notably high molecular weight humic and humic-Fe components), and selenium (Se); but CH₃Hg⁺ and total Hg differed in their specific preferences for binding agents, implying that binding sites discriminate between CH₃Hg⁺ and Hg²⁺ ions. CH₃Hg⁺ was associated with sulfide and (in the spring only) with Fe oxides, whereas total Hg was associated with organic matter and Se and with DTPA- and NaOH-extractable Fe in the spring but with Mn oxide and NaOH-extractable organics in the summer. Sulfides were most abundant in May, indicating that they were eroded from bottom sediments, but Fe and Mn oxides were most abundant in the summer, probably owing to activities of filamentous iron bacteria and other micro-organisms. Particulate Hg was 98–100% nonextractable by mild solvents such as Ca acetate, CaCl₂, dilute acetic acid, and (at polluted sites only) DTPA solutions, suggesting that the particulate Hg mobilized in the spring may not be readily available to organisms; association with Se and high molecular weight humic matter also supports this hypothesis. Hg probably becomes more bio-available in the summer, as suggested by the upsurge in dissolved CH₃Hg⁺ and total dissolved Hg levels, and by increases in the solubility of particulate Hg in acetic acid, DTPA, H₂O₂, and NaOH solutions, as well as an increase in the relative importance of lower molecular weight fractions of NaOH-extractable Hg (in September). Regional variations in Hg speciation and partitioning reflected a gradient in sediment composition from wood chips near Dryden to silt-clay mud further downstream. Hg in silt-clay mud relatively far (> 35 km) downstream from the source of pollution or in unpolluted areas appeared to be more readily solubilized by Cl⁻ ions or chelators such as DTPA, more readily methylated (as indicated by downstream increases in dissolved CH₃Hg⁺ levels and CH₃Hg⁺/total Hg ratios), and was to a greater degree organically bound (H₂O₂-extractable), and thus was probably more bio-available, than Hg in wood-chip deposits. Possible explanations include weaker binding of Hg by the mud, the more finely divided state of the mud, and improved microbial growth at lower concentrations of toxic pollutants. Owing to enrichment in sulfides and Fe oxides, resuspended wood-chip sediments were especially efficient scavengers of CH₃Hg⁺. The results indicate that in any pollution abatement plan aimed at lowering the Hg levels in the biota of lakes fed by the Wabigoon River, immobilization, removal, or detoxification of dissolved as well as particulate forms of Hg in the river would probably have to be considered. Possibly, Hg species could be ‘scrubbed’ from the river water by increasing the suspended load and by sedimentation and treatment with Hg-binding agents in special receiving basins.     

Two cage-type lupin alkaloids from Sophora franchetiana

Two new cage-type lupin alkaloids, (?)-tsukushinamine-B and tsukushinamine-C, have been isolated from the fresh epigeal parts of Sophora franchetiana, along with (?)-cytisine, (?)-N-formylcytisine, (?)-rhombifoline, (?)-anagyrine, (?)-baptifoline and (±)-ammodendrine, as well as (?)-tsukushinamine-A. The structures of these novel tsukushinamine-type lupin alkaloids were determined by spectroscopic data and partly by a chemical reaction. Variations of the alkaloid contents in the seeds, seedlings and various parts of S. franchetiana were also examined.     

Schistosoma mansoni: Electrophoretic characterization of strains selected for different levels of infectivity to snails

Individual adult Schistosoma mansoni from strains selected for high or low infectivity to specific strains of the snail intermediate host, Biomphalaria glabrata, were subjected to enzyme electrophoresis on starch gels. Fourteen enzyme systems were analyzed in an attempt to find electrophoretic markers associated with genes for infectivity to snails. The S. mansoni strains were selected from different isolates from Puerto Rico in several strains of B. glabrata. Of an estimated 18 loci, 3 were polymorphic and the remainder monomorphic. For 1 of the 3 polymorphic enzyme loci, lactate dehydrogenase (Ldh, EC 1.1.1.27), phenotype frequencies were correlated with infectivity to snails. In schistosome strains of low infectivity, frequencies of the Ldh-N phenotype ranged between 0.56 and 0.69, while in strains of high infectivity, Ldh-N frequencies were typically 0.91 to 1.00. Whether the correlation is accidental or due to some form of association, such as chromosomal linkage, between the locus responsible for variation in lactate dehydrogenase and a gene for infectivity to snails remains to be determined.     

Diel variations of selected physico-chemical parameters in Lake Kissimmee,Florida

Every two months, diel depth profiles were made of dissolved oxygen, pH, temperature and conductivity at two stations in Lake Kissimmee, Florida, from July 1974 through June 1975. Results suggest that stratification does not occur in the large (137 km²), shallow (mean depth 2.5 m) lake, though steep vertical gradients in these parameters may develop. The data also suggest that when these gradients do occur, they rapidly degenerate at night or under slight wind stress. Since many Florida lakes are relatively shallow (mean depth < 5 m) and topography offers little obstruction to wind action, it is believed that the holomictic condition observed in Lake Kissimmee may be typical of the state's lakes, particularly those in the central portion of the peninsula.     

Patterns of intra- and interspecific association in leaf-mining insects on three oak host species

Abstract. 1. We determined mortality and distributional patterns of leaf miners on three oak host species (Quercus falcata, Q.nigra and Q.hemisphaerica) in northern Florida, U.S.A.
2. Patterns of intra- and interspecific occurrence within leaves, and mortality of five most abundant leaf miner species were analysed as a test of competition.
3. Miners co-occurred on leaves more often that expected by chance (P<0.05) in six of ten possible species combinations and log-linear model analysis showed no negative higher-order interactions.
4. All five miner species had highly clumped distributions between leaves (P<0.01).
5. Leaf miner survival was less than expected for four of five species when co-occurring on leaves with conspecifics than when mining with heterospecifics or alone (P<0.05).
6. We conclude that interspecific competition is unapparent within this leaf miner guild and that intraspecific competition occurs in four of the five major leaf miner species. We discuss leaf miner selection of common leaves, perhaps based on chemical/physical leaf characters, as a cause of intra- and interspecific aggregation.