Density dependent and density independent relationships during a twenty-seven year study of the population dynamics of the benthic macroinvertebrate community of a chemically unstable lake

Data are given on net precipitation, water chemistry, vegetation cover and the population dynamics of 20 taxa of benthic macroinvertebrates from the total of 40 recorded ln the lake. The relationships between data sets were investigated by bivariate analysis. The relationships between abiotic factors are best described by linear equations as are some relationships between Sigara concinna, Sigara dorsalis, Potamopyrgus jenkinsi and environmental factors. The relationships of numbers of Gammarus tigrinus with temperature, Sigara stagnalis with conductivity, Corixidae with time and Sigara lateralis, Theromyzon tessulatum and Piscicola geometra with vegetation cover are best described by exponential equations. The relationships between the population dynamics of pairs of certain taxa viz. Gammarus tigrinus and G. duebeni, G. tigrinus and Asellus aquaticus, G. tigrinus and Corixidae, Sigara dorsalis and S. concinna, are best described by power equations. The relationship of vegetation cover with time and the population dynamics of many taxa are best described by logarithmic logistic equations.Both density dependent and density independent relationships appear to be responsible for changes in numbers and taxa within the total community. Density independent relationships are most important at times of environmental change while density dependent relationships, though operating continuously, are most important when conditions are stable.     

Is salinity tolerance the key to success for the invasive water bug <Emphasis Type="Italic">Trichocorixa verticalis</Emphasis>?

Trichocorixa verticalis is a North American water bug (Heteroptera: Corixidae) that occurs in brackish and saline aquatic systems. Recently, it has been found invading three continents including Europe. Its invasive success has been attributed to the capacity of tolerating hypersalinity. We compared both the realized and standardized salinity niche of invasive T. verticalis and native Corixidae to verify if T. verticalis may fill in an unoccupied niche. We first established the field distribution of T. verticalis and native Corixidae along a salinity gradient. Second, we experimentally tested the salinity tolerance of T. verticalis and three common native Corixidae species. Of the seven Corixidae species found in the field study, three were positively related to the salinity gradient: S. selecta, S. stagnalis, and T. verticalis. T. verticalis showed the highest salinity optimum, however, after correcting for environmental background variation, salinity optima differed little among the three halophilic species. In the salinity tolerance experiment, S. selecta outperformed T. verticalis, which performed as well as S. stagnalis. Based on our experimental results, we cannot support the hypothesis that T. verticalis’ invasion is mediated by a high salinity tolerance that allows this species to colonize habitats unoccupied by native Corixidae. Although these findings contrast with the field patterns in which T. verticalis showed the highest niche optimum and tolerance, these patterns may have been partly due to other environmental factors, particularly anthropogenic disturbance. Our comparative results are for adults only, and it remains possible that relative salinity tolerance patterns for juveniles differ from that for adults, which may add to the observed field pattern.     

Population dynamics, growth and production of Sigara selecta (Fieber, 1848) (Hemiptera, Corixidae) in a Mediterranean hypersaline stream

1. This is the first study on the life cycle, growth and production of Sigara selecta, a Palearctic corixid species typical of brackish and saline waters, at the warmest limit of its European distributional range. The study combines field and laboratory approaches. 2. The S. selecta population studied was multivoltine, producing four asynchronous cohorts from early spring to December and overwintering in the adult state. Development time from egg to first adult ranged from 2 to 3 months. A minimum temperature threshold of 10 °C and diel amplitude of ≥10 °C were observed for reproduction and oviposition. 3. Maximum density and biomass were reached in mid spring and early autumn. The sex ratio was unbalanced, females dominating during most of the year, except in spring, when the sex ratio was balanced or dominated by males during the first adult emergence. 4. Laboratory rearing experiments at constant temperatures (18, 22 and 26 °C) pointed to a significant effect of temperature on egg development and nymphal growth. In the range of temperatures tested, both egg and nymphal instar duration decreased with increasing temperature. Mean nymphal development time varied from 43 days at 26 °C to 71 days at 18 °C, with a mean of 57 days. Survivorship was independent of temperature. 5. A reduction in nymphal and adult length was observed with increasing temperature. 6. Growth rates decreased with increasing body mass and increased as temperature increased. The first nymphal instar had the highest length increments and growth rates in all temperature treatments. 7. Satisfactory agreement was found between the field and laboratory degree‐days required for complete development from egg to first adult. At constant and variable thermal regimes, degree‐days decreased with increasing temperature. 8. Rate of growth in the field could be predicted with reasonable accuracy from a simple model obtained as a function of body mass. The model explained 67% of the variability in growth rates. 9. Annual production and production/biomass ratio (P/B) of S. selecta estimated by the Instantaneous Growth method were 1.28 g m^?2 year^?1 and 13.71, respectively. Spring and autumn cohorts contributed 32% and 54%, respectively, of total annual production. Maximum production corresponded to intermediate temperature periods, although summer production may have been underestimated because of the longer sampling interval relative to cohort interval production. The Size Frequency method underestimated production by at least 18% with respect to the Instantaneous Growth method.     

The effect of the supernatants obtained fromSporothrix schenkii andCandida albicans culture on the generation of reactive oxygen species by polymorphonuclear leukocytes

The effect of the supernatants obtained from the liquid culture medium ofSporothrix schenkii andCandida albicans on the generation of superoxide anion (O ₂ ^– and hydroxyl radicals OH_., the elements of reactive oxygen species (ROS), and chemilimunescence (CL), a measure of several ROS, by polymorphonuclear leukocytes (PMNs) was examined. In our study, it was shown that the supernatant ofS. schenkii increased all types of ROS generation examined and CL, while that ofC. albicans increased OH_. generation and CL. The effect of the supernatants ofS. schenkii on OH_. generation and CL and that ofC. albicans on CL were most remarkable when the supernatant obtained 8 weeks after the inoculation was used. The supernatant ofS. schenkii was shown to be a much more potent stimulant than the supernatant ofC. albicans. This ROS-stimulating effect of the supernatant ofS. schenkii was heat stable but not dialyzable. These findings suggest the possible role of ROS produced by infiltrated PMNs in the inflammatory skin lesions induced byS. schenkii.     

Inhibition ofAzorhizobium andRhizobium by seed leachates

During germination of seeds ofSesbania rostrata, S. aculeata andS. speciosa various constituents, including tannin, free amino acids, protein, nitrogen and sugars, were released. Tannin released byS. speciosa after 24 h was particularly high. The growth ofAzorhizobium andRhizobium were inhibited in the presence of these materials.     

The Gammaridae and Corixidae of an inland saline lake from 1975 to 1978

When observations began the population of Watch Lane Flash consisted of Gammarus duebeni and Sigara lateralis. Gammarus tigrinus was then introduced; probably during a transfer of water from a nearby canal. G. tigrinus rapidly increased in numbers and at the same time G. duebeni and S. lateralis decreased to zero. There followed a partial recolonisation by corixids but the species present were Sigara concinna and Sigara dorsalis. Throughout the study period corixid populations were stable in two immediately adjacent water bodies, one of which also contained G. duebeni. Thus the changes described were associated with the presence of G. tigrinus. The reasons for the success of G. tigrinus and its effects on other gammarids and corixids are discussed.     

Experimental transmission and pathogenicity of some zoosporic fungi toTilapia fish

Seventeen fungal species belong to six genera were recovered from the four organs ofTilapia fish and the most common wereSaprolegnia ferax, S. diclina, Achlya dubia, A. americana, A. racemosa andA. flagellata, Dictyuchus sterile,Pythium undulatum andAphanomyces sp. Severe infection followed by death of all fish was incited byS. parasitica andS. ferax through experiment I. 30–70% ofT. nilotica andT. galileae were killed through experiment II byS. parasitica andS. ferax. T. galileae was more susceptible to fungal infection thanT. nilotica.     

Host choice and fitness correlates for conopid flies parasitising bumblebees

Two parasitoid flies,Physocephala rufipes andSicus ferrugineus (Diptera, Conopidae), and their hosts,Bombus spp., coexist at various locations in northwestern Switzerland. A detailed field study showed that both conopid species use the hostB. pascuorum to a similar degree, while the hostB. terr-luc (a pooled category ofB. terrestris andB. lucorum) is more frequently parasitised than expected byS. ferrugineus. The hostB. lapidarius in turn is exclusively used byP. rufipes. Furthermore, hosts ofB. terr-luc andB. pascuorum parasitised byS. ferrugineus were larger than hosts parasitised byP. rufipes, or than those not parasitised. The findings suggest thatS. ferrugineus selects larger hosts and may displaceP. rufipes. Pupal weight, a predictor of adult body size and parasitoid fecundity, is positively correlated with host size and larger pupae are more likely to emerge, while host species had no effect on the probability of emergence in either conopid species. Host species affected pupal weight inS. ferrugineus, but not inP. rufipes, althoughP. rufipes grew larger in hosts of a given size. Daughters emerged from larger pupae than males, but this did not correlate with larger host sizes. These observations add to the scarce knowledge of dipteran parasitoids.     

Symphurus hondoensis Hubbs, 1915, a valid species of western Pacific tonguefish (Pleuronectiformes: Cynoglossidae)

Symphurus hondoensis Hubbs, 1915, originally described only from the holotype taken in 390–542 m in Suruga Bay Japan, has long been considered a junior synonym ofS. strictus Gilbert, 1905, known from waters off Hawaii, Japan, the Philippine Islands, and South Africa. Based on new information from the holotype and a specimen recently captured from deep waters (789–815 m) off Amami-Oshima Island, southern Japan,S. hondoensis is now established as a valid species.Symphurus hondoensis is unique among congeners in having the combination of a 1–2–3 pattern of interdigitation of proximal dorsal pterygiophores and neural spines, 10 abdominal vertebrae, 14 caudalfin rays, 111–113 dorsal-fin rays, 95 anal-fin rays, 59 total vertebrae, 105–106 scales in longitudinal series, blind side nearly as darkly pigmented as the ocular surface, and a black peritoneum. Recognition ofS. hondoensis increases the number of described species ofSymphurus in waters off Japan to three (S. orientalis Bleeker,S. strictus, andS. hondoensis), with at least one more underscribed species occurring in deepwater hydrothermal vent areas off southern Japan.     

Chemical composition of the cell wall in some green algae species

Cell walls of two strains ofChlorella vulgaris (from fresh water, F, and saline water, S) and ofKirchneriella lunaris contained various proportion of saccharides and proteins (highest percentage in dry matter was found inK. lunaris). They differed also in presence of individual monosaccharides (5 inC. vulgaris F, 8 inC. vulgaris S and 6 inK. lunaris) and amino acids (11 in C.vulgaris F, 6 in C.vulgaris S and 7 inK. lunaris). Common substances were rhamnose, cystine, proline, glutamic acid and leucine. Communicated by Z. ŠESTáK     

Interaction of Salivary alpha-Amylase and Amylase-Binding-Protein A (AbpA) of <Emphasis Type="Italic">Streptococcus gordonii</Emphasis> with Glucosyltransferase of <Emphasis Type="Italic">S. gordonii</Emphasis> and <Emphasis Type="Italic">Streptococcus mutans</Emphasis>

Background  

Glucosyltransferases (Gtfs), enzymes that produce extracellular glucans from dietary sucrose, contribute to dental plaque formation byStreptococcus gordoniiandStreptococcus mutans. The alpha-amylase-binding protein A (AbpA) ofS. gordonii, an early colonizing bacterium in dental plaque, interacts with salivary amylase and may influence dental plaque formation by this organism. We examined the interaction of amylase and recombinant AbpA (rAbpA), together with Gtfs ofS. gordoniiandS. mutans.     

Parasitoid-host relationship betweenTrioxys (Binodoxys) Indicus [Hymenoptera: Aphidiidae] andAphis Craccivora [Hemiptera: Aphididae]. VI. Impact of males on the number of progeny of the parasitoid reared on certain host plants

The present paper elucidates the impact of males on the reproductive rate ofTrioxys (Binodoxys) indicus reared on the aphids ofCajanus cajan, Dolichos lablab andSolanum melongena host plants. The F₁ offspring increases with the increase of parasitoid number. This increase is maximum inC. cajan followed byD. lablab andS. melongena reared aphids. The presence of male parasitoids caused a significant decrease in the emergence of F₁ generation.      

The ecology of the Corixidae (Hemiptera: Heteroptera) in the Corrib catchment,Ireland

Two surveys were carried out in the Corrib catchment (Ireland) to determine the physical and chemical factors that govern the distribution of Corixidae. Of the twenty one species recorded, five species, Sigara scotti (Fieber), S. distincta (Fieber), S. fossarum (Leach), S. fallenoidea (Hungerford) and Cymatia bonsdorffii (Sahlberg) comprised 82% of the numerical total. Although individual species occurred in chemically diverse sites species assemblages and changes in the relative abundance of the majority of species and in species richness and diversity were evident in the progression from hard to soft water. High altitude soft water sites had a much lower number of species compared with chemically similar low altitude sites. In Lough Corrib, the main body of water in the catchment, most species were abundant only in sheltered areas with mud substrates and high percentage vegetation cover. Species diversity was high in these areas and either C. bonsdorffii, S. fossarum, S. fallenoidea or Callicorixa praeusta (Fieber) dominated numerically. However, S. scotti, S. dorsalis (Leach) and Arctocorisa germari (Fieber) were more abundant in exposed areas with sand, gravel or mearl substrates. In temporary ponds and in lotic water species diversity was also high but species composition (mainly C. praeusta, Sigara nigrolineata (Fieber), Corixa punctata (Illiger), C. panzeri (Fieber), C. bonsdorffii) was different to that of temporally stable lentic habitats.     

Co-inoculation with antibiotic-producing bacteria to increase colonization and nodulation by rhizobia

A study was conducted to determine whether colonization of legume roots and nodulation byRhizobium meliloti andBradyrhizobium japonicum could be enhanced by using inocula containing microorganisms that produce antibiotics suppressing soil or rhizosphere inhabitants but not the root-nodule bacteria. An antibiotic-producing strain of Pseudomonas and one of Bacillus were isolated, and mutants ofR. meliloti andB. japonicum sp. resistant to the antibiotics were used. The colonization of the alfalfa rhizosphere and nodulation byR. meliloti were enhanced by inoculation of soil withPseudomonas sp. in soil initially containing 2.7×10⁵ R. meliloti per g. The colonization of soybean roots byB. japonicum was enhanced by inoculating soil with three cell densities ofBacillus sp., and nodulation was stimulated byBacillus sp. added at two cell densities. In some tests, the dry weights of soybeans and seed yield increased as a result of these treatments, and co-inoculation with Bacillus also increased pod formation. Inoculation of seeds withBacillus sp. and the root-nodule bacterium enhanced nodulation of soybeans and alfalfa, but colonization byB. japonicum andR. meliloti was stimulated only during the early period of plant growth. Studies were also conducted withStreptomyces griseus and isolates ofR. meliloti andB. japonicum resistant to products of the actinomycete. Nodulation of alfalfa byR. meliloti was little or not affected by the actinomycete alone; however, both nodulation and colonization were enhanced if the soil was initially amended with chitin andS. griseus was also added. Chitin itself did not affectR. meliloti. Treatments of seeds with chitin orS. griseus alone did not enhance colonization of alfalfa roots byR. meliloti or soybean roots byB. japonicum, but the early colonization of the roots by both bacterial species was promoted if the seeds received both chitin andS. griseus; this treatment also increased nodulation and dry weights of alfalfa and soybeans and the N content of alfalfa. It is suggested that co-inoculation of legumes with antibiotic-producing microorganisms and root-nodule bacteria resistant to those antibiotics is a promising means of promoting nodulation and possibly nitrogen fixation.     

The composition,structure and distribution of heathland and grassland communities in the subalpine tract of the Bogong High Plains,Victoria

In the subalpine tract of the Bogong High Plains (37°S, 147°E; altitude 1600–1800 m a.s.l.) the vegetation consists of a mosaic of snow gum (Eucalyptus pauciflora) woodland, heathland, grassland and wetland communities. Classification (polythetic-agglomerative) and ordination (principal co-ordinates analysis) of quadrat data from heathlands and grasslands on relatively well drained sites allowed the identification of four main heathland and grassland vegetation units. These units may be ranked in a structural and floristic continuum, from closed heath variously dominated by Prostanthera cuneata, Orites lancifolia and Phebalium squamulosum to closed heath dominated by P. squamulosum and Grevillea australis, open grassy heath of G. australis and Poa hiemata. and grassland of P. hiemata. The transition from Prostanthera closed heath to Poa grassland is correlated with gradients of decreasing steepness and rockiness of terrain, and increasing exposure and frost.     

New chromosome counts inStreptocarpus (Gesneriaceae) from Madagascar and the Comoro Islands and their taxonomic significance

This study records the chromosome numbers of 10 species ofStreptocarpus; nine of the counts are new. With the exception ofS. buchananii of mainland Africa, all the results are for plants endemic to Madagascar and the Comoro Islands. While there is a strong correlation between basic number and growth form in the two subgenera of the genus on the African mainland (x = 15 among caulescent species in subgenusStreptocarpella; x = 16 among acaulescent species in subgenusStreptocarpus), the situation appears more complex among Madagascan and Comoro Island species. One notable example of deviation from this correlation is shown byS. papangae, a shrubby caulescent species, with 2n = 32 (x = 16). Polyploidy in the genus appears to be absent on mainland Africa, but is present in Madagascar and the Comoro Islands, ranging from tetraploidy to octoploidy. Evolutionary implications of the cytological observations are considered.     

Differentiation ofStreptomyces strains by gas chromatography

Culture fluids of representative strains ofStreptomyces griseus, S. griseoluteus, S. albus, S. viridochromogenes andS. fradiae were distilled at 100 C, the distillates extracted with ether and the concentrated extracts analyzed by dual-channel gas chromatography. Each extract gave a distinctly different chromatogram. The greatest number of clearly separable peaks and the highest yields of volatile products were formed byS. griseus. The possible use of gas chromatography in taxonomic studies of actinomycetes is discussed.     

Proline production via the arginine biosynthetic pathway: transfer of regulatory mutations of arginine biosynthesis into a proline-producing strain ofSerratia marcescens

Summary Proline production via a part of the arginine biosynthetic pathway was examined. About 20 mg/ml ofl-proline was produced by using arginine biosynthetic enzymes. Accordingly, three mutations of arginine biosynthesis, namely, derepression of arginine biosynthetic enzymes (assigned byargR2), feedback inhibition-resistant N-acetylglutamate synthase (assigned byargA2) and defectiveness in N-acetylornithine aminotransferase (assigned byargD ^–) were introduced by three transductional crosses into a proline-producing strain which produced about 55 mg/ml ofl-proline. The constructed strain produced 62 mg/ml ofl-proline, although about 10 mg/ml ofl-arginine and 1 mg/ml of N-acetylglutamate--semialdehyde were produced as by-products.