Environmental factors regulate the effects of roach Rutilus rutilus and pike Esox lucius on perch Perca fluviatilis populations in small boreal forest lakes

In this study of 18 small boreal forest lakes, the effects of abiotic and biotic factors (roach Rutilus rutilus and pike Esox lucius) on various population variables of perch Perca fluviatilis were examined. As a single variable, the gillnet catch per unit effort (CPUE) of R. rutilus was negatively related to the mean mass of small (< 200 mm) and the growth rate of young (1–2 years) P. fluviatilis. The mean mass of large (≥ 200 mm) P. fluviatilis was the highest at intermediate CPUE of R. rutilus. Redundancy analysis including environmental factors and P. fluviatilis population variables suggested that ‘predation–productivity–humus' gradient affected P. fluviatilis populations by decreasing the CPUE and mean mass of small individuals but increasing these variables of large individuals. The CPUE of R. rutilus and lake area had a negative effect on small and a positive effect on large P. fluviatilis growth rate. In small boreal forest lakes, P. fluviatilis populations are affected by the partially opposite forces of competition by R. rutilus and predation by E. lucius, and the intensity of these interactions is regulated by several environmental factors.     

Cytoskeletal alterations in interphase cells of the green alga Spirogyra decimina in response to heavy metals exposure: I. The effect of cadmium

Summary. The aim of the study was to elucidate the effect of cadmium ions on the arrangement of the actin and tubulin cytoskeleton, as well as the relationships between cytoskeletal changes and growth processes in the green filamentous alga Spirogyra decimina. Batch cultures of algae were carried out under defined conditions in the presence of various cadmium concentrations. In control cells, the cytoskeleton appeared to be a transversely oriented pattern of both microtubules and actin filaments of various thickness in the cell cortex; colocalization of cortical microtubules and actin filaments was apparent. Microtubules were very sensitive to the presence of cadmium ions. Depending on the cadmium concentration and the time of exposure, microtubules disintegrated into short rod-shaped fragments or they completely disappeared. A steep increase in cell width and a decrease in growth rate accompanied (and probably ensued) a very rapid disintegration of microtubules. Actin filaments were more stable because they were disturbed several hours later than microtubules at any cadmium concentration used. When cadmium ions were washed out, the actin cytoskeleton was rebuilt even in cells in which actin filaments were completely disintegrated at higher cadmium concentrations (40 or 100 μM). The much more sensitive microtubules were regenerated after treatment with lower cadmium concentrations (10 or 15 μM) only. Correspondence and reprints: Centre of Phycology, Institute of Botany, Academy of Sciences of the Czech Republic, Dukelská 135, 379 82 Třeboň, Czech Republic.     

Village-scale evaluation of mosquito nets treated with a tablet formulation of deltamethrin against malaria vectors

A field trial was carried out in the Sundargarh district of Orissa, India on the efficacy of mosquito nets treated with a tablet formulation of deltamethrin (K-O TAB) against malaria vectors. Treated nets were used in one village, and in the two control villages, one used untreated nets and the other used indoor spraying with DDT, without nets. In this area the primary malaria vectors are Anopheles culicifacies Giles sensu lato (Diptera: Culicidae) and An. fluviatilis James s.l., which are both endophagic and endophilic, and fully susceptible to deltamethrin. Treatment of a 10-m(2) mosquito net with one of the tablets gave a deltamethrin deposit of 25 mg/m(2). Bioassays repeated on domestically used nets over 7 months showed persistence of almost 100% mortality of An. fluviatilis, whereas An. culicifacies showed a decline from 100% to 71% mortality over this period, after which the nets were re-treated and bioassays were not continued. The sum of collections of mosquitoes resting in village houses and those in exit traps and dead on floor sheets showed a reduction in the numbers of the two vector species due to the treated nets, compared with untreated or no nets, but no reduction in other anophelines or Culex species. Large proportions of the collections of the vector and non-vector anophelines were dead on the floor sheets, but among Culex, mortality was delayed. Treated and untreated nets reduced the proportion of anophelines that had blood-fed; the treated nets did so more effectively than the untreated in the case of An. culicifacies and of Culex mosquitoes. In rooms with treated nets a larger proportion of the total collections [dead + live] were in the exit traps, which can be attributed to the excito-repellent effect of deltamethrin. It is easier to pack and handle tablets of insecticide than liquid concentrate and the use of one tablet per net may be preferable to making up a large volume of diluted insecticide and dipping many nets at a time.     

A POLYPLOID SPECIES COMPLEX OF SPIROGYRA COMMUNIS (CHLOROPHYTA) OCCURRING IN NATURE 1

Investigations were conducted to determine whether ploidal changes found in laboratory cultures of Spirogyra also occur in nature. In an earlier study filament types identifiable as three different species (Spirogyra singu-laris Nordstedt, S. communis (Hassall)Kütz., S. fragilis Jao) arose from an original clonal culture through vegetative growth and sexual reproduction. These three “species” or filament groups differed in filament width, chloroplast number, zygospore size, and chromosome number. The differences in chromosome number represented a polyploid series of diploid (S. communis), triploid (S. fragilis), and tetraploid (S. singularis) forms in which width increased with ploidal level. The three width groups constituted a “species complex.” Five years after isolation of the original strain in this species complex, filaments corresponding to two of the width groups (S. singularis and S. communis) were found at the original collection site in the Santa Catalina Mountains in southern Arizona. The two field-collected groups were indistinguishable from the laboratory species complex in morphology and chromosome number. Homothallic conjugation within the two field width groups yielded progeny similar to those from homothallic conjugation of groups in the laboratory species complex. Filament widths of progeny were generally within the width limits of respective parental groups. The four possible intergroup crosses between the two laboratory and two field width groups yielded progeny similar to the wider parent (S. singularis) or the parent of intermediate width (S. fragilis). Progeny characteristics were determined by the width groups of parents, regardless of whether parents came from the laboratory or field. The similarities in morphology, chromosome numbers, and reproductive behavior of laboratory and field width groups imply that the laboratory species complex of S. communis has a natural counterpart in the field.     

A MOVING MAT: PHOTOTAXIS IN THE FILAMENTOUS GREEN ALGAE SPIROGYRA (CHLOROPHYTA,ZYGNEMATACEAE)1

A blue light– (peak at 470 nm) induced photomovement was observed in the filamentous eukaryotic algae, Spirogyra spp. When Spirogyra filaments were scattered in a water chamber under a unilateral light source, they rapidly aligned toward the light source in 1 h and bound with neighboring filaments to form thicker parallel bundles of filaments. The filaments in the anterior of the bundles curved toward the light first and then those in the posterior began to roll up toward the light, forming an open‐hoop shape. The bundle of filaments then moved toward the light source by repeated rolling and stretching of filaments. When the moving bundle met other filaments, they joined and formed a bigger mat. The coordination of filaments was essential for the photomovement. The average speed of movement ranged between 7.8 and 13.2 μm·s^?1. The movement was induced in irradiance level from 1 to 50 μmol photons·m^?2·s^?1. The filaments of Spirogyra showed random bending and stretching movement under red or far‐red light, but the bundles did not move toward the light source. There was no distinct diurnal rhythm in the photomovement of Spirogyra spp.     

FACULTATIVE PARASITISM OF SPIROGYRA SP. (CHLOROPHYTA) BY SAPROLEGNIA ASTEROPHORA AND PYTHIUM GRACILE (EUMYCOTA,OOMYCETES)1

Spirogyra sp. Link was found to be parasitized by filamentous fungi tentatively identified as Saprolegnia asterophora de Bary and Pythium gracile Schenk, in field samples and when maintained in unaltered pond water in an 18 h fluorescent light–6 h dark regime at 18 ± 2°C. Collections were made periodically between March 1978, and November 1979, from a pond in Mill Seek Sanctuary near Oyster Bay, Nassau Co., Long Island, New York. Initially, less than 1% of the total field population of Spirogyra sp. was infected by either fungal parasite with Saprolegnia asterophora being the dominant parasite present generally alone in most samples or present in 80–95% of the total number of infected algal filaments when occurring concurrently with P. gracile. However, in the laboratory, approximately 100% of the Spirogyra sp. filaments in any given sample became infected by Saprolegnia asterophora and/or P. gracile within a 1—2 wk and 3–4 wk period, respectively, with vegetative hyphae involved in the spread of infection to neighboring algal filaments. Infection of algal filaments occurred at random points with cell to cell hyphal extension within the filament causing disruption of host cells. Development of S. asterophora, and possibly P. gracile, sexual reproductive structures was common in relation with the host with asexual sporangial production not observed. Saprolegnia asterophora and P. gracile were cultured on glucose, yeast extract, malt extract (GYM) medium from infected Spirogyra sp. filaments, with infection of healthy algal filaments using these cultures by Saprolegnia asterophora, but not by P. gracile, induced in the laboratory. Growth responses and tropic responses of the fungi to the algal host could not be demonstrated.     

The cytoplast concept in dividing plant cells: cytoplasmic domains and the evolution of spatially organized cell

The unique cytokinetic apparatus of higher plant cells comprises two cytoskeletal systems: a predictive preprophase band of microtubules (MTs), which defines the future division site, and the phragmoplast, which mediates crosswall formation after mitosis. We review features of plant cell division in an evolutionary context and from the viewpoint that the cell is a domain of cytoplasm (cytoplast) organized around the nucleus by a cytoskeleton consisting of a single "tensegral" unit. The term "tensegrity" is a contraction of "tensional integrity" and the concept proposes that the whole cell is organized by an integrated cytoskeleton of tension elements (e.g., actin fibers) extended over compression-resistant elements (e.g., MTs).During cell division, a primary role of the spindle is seen as generating two cytoplasts from one with separation of chromosomes a later, derived function. The telophase spindle separates the newly forming cytoplasts and the overlap between half spindles (the shared edge of two new domains) dictates the position at which cytokinesis occurs. Wall MTs of higher plant cells, like the MT cytoskeleton in animal and protistan cells, spatially define the interphase cytoplast. Redeployment of actin and MTs into the preprophase band (PPB) is the overt signal that the boundary between two nascent cytoplasts has been delineated. The "actin-depleted zone" that marks the site of the PPB throughout mitosis may be a more persistent manifestation of this delineation of two domains of cortical actin. The growth of the phragmoplast is controlled by these domains, not just by the spindle. These domains play a major role in controlling the path of phragmoplast expansion. Primitive land plants show different morphological changes that reveal that the plane of division, with or without the PPB, has been determined well in advance of mitosis.The green alga Spirogyra suggests how the phragmoplast system might have evolved: cytokinesis starts with cleavage and then actin-related determinants stimulate and positionally control cell-plate formation in a phragmoplast arising from interzonal MTs from the spindle. Actin in the PPB of higher plants may be assembling into a potential furrow, imprinting a cleavage site whose persistent determinants (perhaps actin) align the outgrowing edge of the phragmoplast, as in Spirogyra. Cytochalasin spatially disrupts polarized mitosis and positioning of the phragmoplast. Thus, the tensegral interaction of actin with MTs (at the spindle pole and in the phragmoplast) is critical to morphogenesis, just as they seem to be during division of animal cells. In advanced green plants, intercalary expansion driven by turgor is controlled by MTs, which in conjunction with actin, may act as stress detectors, thereby affecting the plane of division (a response clearly evident after wounding of tissue). The PPB might be one manifestation of this strain detection apparatus.     

Genetic divergence and phylogeographic relationships among european perch (Perca fluviatilis) populations reflect glacial refugia and postglacial colonization

We used the widely distributed freshwater fish, perch (Perca fluviatilis), to investigate the postglacial colonization routes of freshwater fishes in Europe. Genetic variability within and among drainages was assessed using mitochondrial DNA (mtDNA) D-loop sequencing and RAPD markers from 55 populations all over Europe as well as one Siberian population. High level of structuring for both markers was observed among drainages and regions, while little differentiation was seen within drainages and regions. Phylogeographic relationships among European perch were determined from the distribution of 35 mtDNA haplotypes detected in the samples. In addition to a distinct southern European group, which includes a Greek and a southern Danubian population, three major groups of perch are observed: the western European drainages, the eastern European drainages including the Siberian population, and Norwegian populations from northern Norway, and western side of Oslofjord. Our data suggest that present perch populations in western and northern Europe were colonized from three main refugia, located in southeastern, northeastern and western Europe. In support of this, nested cladistic analysis of mtDNA clade and nested clade distances suggested historical range expansion as the main factor determining geographical distribution of haplotypes. The Baltic Sea has been colonized from all three refugia, and northeastern Europe harbours descendants from both eastern European refugia. In the upper part of the Danube lineages from the western European and the southern European refugia meet. The southern European refugium probably did not contribute to the recolonization of other western and northern European drainages after the last glaciation. However, phylogenetic analyses suggest that the southern European mtDNA lineage is the most ancient, and therefore likely to be the founder of all present perch lineages. The colonization routes used by perch probably also apply to other freshwater species with similar distribution patterns.     

Variation in food intake within groups of juvenile perch

The coefficient of variation of individual food intake was large in small groups of young-of-the-year perch Perca fluviatilis (45–60 mm L _T) and smaller when fish that were given the same feeding rank were placed together. No aggressive interactions were detected during feeding.     

An application of a bioenergetics model to Eurasian perch (Perca fluviatilis L.)

A bioenergetics model was developed for Eurasian perch ( Perca fluviatilis L.) by revising an existing model for yellow perch and walleye. Data were gathered from field studies and the literature. Besides adjusting the original parameters of the model, effects of season on consumption and metabolic rates were added. The predictive capability of the revised model was high both concerning the levels of growth and its seasonal development in the Baltic coastal waters to which the model was applied. Perch young-of-the-year attained almost maximum consumption and growth except in the highest temperatures experienced. In larger fish, the model estimated consumption to be about 50 per cent of the maximum possible rate.