Importance of consumptive and non-consumptive prey mortality in a coupled predator–prey system

1. Laboratory experiments were completed to identify the mechanisms by which the predatory flatworm, Dugesia tigrina , imposes mortality on its Aedes aegypti and Daphnia magna prey. Feeding trials were completed in glass microcosms which contained one of three – nine densities of small or large individuals of each prey species.
2. Mortality by Dugesia on small and large Aedes followed a type II functional response, whereas the mortality of Daphnia resembled a type III functional response. Prey mortality imposed by Dugesia consisted of consumptive and non-consumptive elements. Non-consumptive mortality occurred when prey individuals trapped in mucus trails subsequently died but were not ingested.
3. Additional experiments were conducted to quantify consumptive (capture followed by ingestion) and non-consumptive mortality (death not followed by ingestion).
4. Consumptive mortality followed a type II functional response for small and large individuals of both prey species, whereas non-consumptive mortality increased with prey density, although the relationships differed with prey species and size. The non-consumptive mortality of large Daphnia increased at an accelerating rate with prey density and exceeded consumptive mortality at intermediate prey abundances. In contrast, non-consumptive mortality of small Aedes and small Daphnia was lower than consumptive mortality and either increased with prey density at a decelerating (small Aedes ) or accelerating (small Daphnia ) rate.
5. These results suggest that the importance of consumptive and non-consumptive mortality to total prey mortality needs to be considered when modelling predator–prey dynamics.     

Shell-banding polymorphism of the land snail Xeropicta vestalis along the coastal plain of Israel

Along the coastal plain of Israel, shell darkness of the polymorphic land snail Xeropicta vestalis is positively related to the extent of perennial vegetation. It is not related to rain, temperature, geographic position or darkness of the ground.
White shells reflect more radiation than dark ones do, and therefore in Israel's coastal plain, where solar radiation is very strong, they are favoured. Perennial vegetation, where it occurs, shields the snails from the sun by absorbing radiation, so that snails amongst them can afford to be darker, and thus more cryptic. Hence, the more perennial vegetation in the habitat, the darker the shells.
Also during the Pleistocene, when temperatures were 5–10°C lower than today, the shells of the coastal plain were as pale as recent ones are. The distribution of a snail-predator, Gerbillus allenbyi , which is restricted to sandy biotopes where perennial bushes occur, and which was absent from Israel during the Pleistocene, could perhaps explain the distribution of X. vestalis morphs, both today and in the past.     

Population genetic structure, phylogeography and spawning philopatry in walleye (Stizostedion vitreum) from mitochondrial DNA control region sequences

Mitochondrial (mt) DNA control region sequences were used to test the genetic and phylogeographic structure of walleye Stizostedion vitreum populations at different geographical scales: among spawning sites, lake basins, lakes, and putative glacial refugia in the Great Lakes region. Sequencing 199 walleye revealed nucleotide substitutions and tandemly repeated sequences that varied in copy number, as well as in sequence composition, in 1200 bp of the mtDNA control region. Variable numbers of copies of an 11-bp tandem repeat showed no geographical patterning and were not used in further analyses. Substitutions in the other areas of the control region yielded 19 haplotypes, revealing phylogeographic structure and significant differences among glacial refugia, lakes, basins and some spawning sites. Differences among spawning populations were consistent with reduced gene flow, philopatry and possible natal homing. Analysis of spawning populations showed consistency of genotypic frequencies among years and between males and females, supporting philopatry in both sexes. The unglaciated plateau in southern Ohio, USA housed a very different haplotype that diverged prior to the Missouri, Mississippi and Atlantic glacial refugia types. Haplotypes from the three refugia colonized the Great Lakes after retreat of the Wisconsin glaciers, and their present distribution reflects the geography of their prior isolation and differential colonization. Populations that became associated with spawning localities appear to have diverged further due to philopatry, resulting in fine-scale phylogeographic structuring.     

ASSESSMENT OF IMPEDANCE MICROBIOLOGICAL METHOD FOR THE DETECTION OF ESCHERICHIA COLI IN FOODS

This study was conducted to determine the sensitivity and specificity of the impedance-based microbiological method for the detection of Escherichia coli in foods within 24 h of testing. A Malthus Microbiological Analyzer system (Malthus System V, Malthus Instruments Ltd., Bury, United Kingdom), and a modified Malthus Coliform Broth Medium (MCBM), and an incubation temperature of 44C were used. The sensitivity of the impedance method was determined by testing E. coli-negative food samples spiked with different concentrations of E. coli. The specificity of the method was determined by testing E. coli -negative food samples spiked with Klebsiella pneumoniae, Enterobacter cloacae and Pseudomonas aeruginosa. The test results were compared with those obtained by the Most Probable Number (MPN) method. Milk, milk products, raw and ready-to-eat meats, and vegetables were tested for the presence of E. coli by both methods. The sensitivity of the impedance method and the MPN method for the detection of foods containing 10¹ CFU/g was 100% and 84.4%, respectively. Both methods had a specificity of 100% for food samples spiked with 10¹ CFU/g E. coli. The specificity of the impedance and the MPN methods for the detection of E. coli in naturally contaminated milk and meat samples was 100% and 95.7% respectively. E. coli was detected in foods by the impedance method within 4–24 h of testing at a detection limit of 1 CFU/mL. These results demonstrate that the impedance method can be used as a rapid and sensitive method for the detection of E. coli in foods.     

Nuclear Division in the Ameboflagellate Adelphamoeba galeacystis

Nuclear division in synchronized cultures of the ameboflagellate Adelphamoeba galeacystis has been described. Division in this organism is typically promitotic. It occurs within an intact nuclear membrane and is characterized by the persistence of the nucleolus and its transformation into 2 polar masses. The nucleolus is stained with pyronin-Y by the methyl green pyronin-Y technic, and with Heidenhain's hematoxylin, but is unstained by the Feulgen reaction. The reaction with these stains is removed after digestion of the nucleolus by ribonuclease. During mitosis the nucleolus undergoes an orderly series of vacuolizations before forming the polar masses. The chromatin is Feulgen positive, stains with methyl green by the methyl green pyronin-Y technic and undergoes a series of characteristic changes during the division process. Synchronization of amebae grown on coverglasses was accomplished by transfer of cells from 30 to 38.5 C for a period of 100 min. A temporal sequence of nucleolar and chromatin participation in the nuclear division of this organism is suggested.     

Salinity and the Hydraulic Conductance of Roots

The effect of salinity on hydraulic conductance of intact roots of tomato (Lycopersicon esculentum Mill.) and sunflower (Helianthus annuus L.) was determined in split-root experiments using salinized nutrient solutions. Experiments were conducted in controlled climate chambers under two or three relative humidity levels and four solution osmotic potential levels. The relationship between water flux through roots (J_v) and total water potential difference between the leaves and the root medium (Δψ) was linear, usually with a small intercept. Thus, the root hydraulic conductance (L) was not affected by salinity within the range of fluxes obtained in these experiments, with L= 0.036 mm h^?1 bar^?1 for tomato and L= 0.0167 mm h^?1 bar^?1 for sunflower. Our results agreed with theoretical analysis of coupled water and ion uptake. From Cl^? and Na⁺ uptake data, the reflection coefficient (o) for tomato roots was calculated as 0.956, which was compatible with the near-zero intercept. A large intercept for sunflower could not be readily explained. Relative humidity strongly affected root growth, with more rapid growth under low humidity conditions. Transpiration of sunflower plants was reduced by 20% when the relative humidity was increased from 34% to 84%, whereas transpiration in tomato was reduced 50%.     

Evolution and Diversification of Antarctic Notothenioid Fishes

Antarctica supported fossil ichthyofaunas during the Devonian,Jurassic, Cretaceous and Eocene/Oligocene. These faunas arenot ancestral to each other, nor are they related to any componentof the modern fauna. About one hundred species of notothenioidsdominate a modern fauna of over 200 species of bottom fishes.This highly endemic perciform suborder is not representedinthe fossil record of Antarctica. Notothenioids may have evolvedin situ on the margins of the Antarctic continent while graduallyadapting to cooling conditions during the Tertiary. Cladisticstudies indicate that notothenioids are a monophyletic group,but a sister group has not been identified among perciform fishes.With relatively few non-notothenioid fishes in Antarctic waters,notothenioids fill ecological roles normally occupied by taxonomicallydiverse fishes in temperate waters. There are six notothenioidfamilies: Bovichtidae, Nototheniidae, Harpagiferidae, Artedidraconidae,Bathydraconidae and Channichthyidae. Aspects of theirbiologyare briefly considered with emphasis on the Nototheniidae, themost speciose family. Evolutionary diversification within thisfamily allows recognition of species which are pelagic, cryopelagic,benthopelagic and benthic.     

Observations on the Endogenous Stages of Eimeria confusa Joseph, 1969 from the Grey Squirrel Sciurus carolinensis*

SYNOPSIS. Stages in the endogenous cycle of Eimeria confusa from the grey squirrel, Sciurus carolinensis, are described from mixed infections with another species, Eimeria lancasterensis. All corresponding stages were markedly different in the 2 species. In E. confusa infections, the parasites were located below the host cell nuclei of the epithelial cells of the villi of the jejunum and ileum. Mature schizonts were ellipsoidal, averaged 20.9 × 18.6 μm and had 18–30 merozoites. The mature microgamonts measured 34.3 × 24.7 μm and had hundreds of microgametes. Mature macrogametes were ovoid, averaged 31.3 × 25.6 μm, and contained 2 kinds of plastic granules.     

Critical Phases of Oral Primordium Development in Tetrahymena pyriformis GL-C: An Analysis Employing Low Temperature Treatment

SYNOPSIS. The effects of temperatures of 12–18 C on cell division and oral primordium development were investigated in cultures of synchronized Tetrahymena pyriformis GL-C. If exposures to 12 or 15 C were initiated prior to a “transition point,” long delays of cell division were generated. After this transition point, cell division could no longer be substantially delayed by exposure to low temperature. The time of the transition point was somewhat earlier with 15 C than with 12 C treatments. At temperatures higher than 15 C long delays of cell division were not generated regardless of time of treatment. The effects of low temperature on oral morphogenesis were strongly dependent on the stage which was affected. (i) The further development of cells initially in the “anarchic field” stage (stage 1) was immediately blocked at both 12 and 15 C. (ii) Cells initially in the stages of incipient membranelle differentiation (stages 2 and 3) continued to develop at both 12 and 15 C, and formed oral primordia in which all 3 membranelles were clearly differentiated (stage 4). The subsequent progress of these stage 4 primordia depended on the temperature: at 12 C virtually all were resorbed (and cell division was blocked); at 15 C only about 1/3 were resorbed, while the remaining 2/3 completed their development (with the concomitant completion of cell division). (iii) Cells initially in intermediate stages of membranelle differentiation (early stage 4) developed to some extent at 12 C, and then underwent resorpton of oral primordia and blockage of cell division; at 15 C such cells completed their development and division normally. (iv) Cells in which the membranelles and undulating membrane were complete or nearly so (stage 5 and very late stage 4) at the time of the beginning of the cold treatment subsequently finished their development and went thru cell division, even at temperatures as low as 5 C. These results indicate that in addition to a “stabilization point” which occurs shortly before the completion of membranelle development, there is an earlier change in the primordium at the time of the onset of membranelle development, which renders development much less sensitive to direct interference by low temperature.