Latitudinal variation in the shape of the species body size distribution: an analysis using freshwater fishes

Many taxonomic and ecological assemblages of species exhibit a right-skewed body size-frequency distribution when characterized at a regional scale. Although this distribution has been frequently described, factors influencing geographic variation in the distribution are not well understood, nor are mechanisms responsible for distribution shape. In this study, variation in the species body size-frequency distributions of 344 regional communities of North American freshwater fishes is examined in relation to latitude, species richness, and taxonomic composition. Although the distribution of all species of North American fishes is right-skewed, a negative correlation exists between latitude and regional community size distribution skewness, with size distributions becoming left-skewed at high latitudes. This relationship is not an artifact of the confounding relationship between latitude and species richness in North American fishes. The negative correlation between latitude and regional community size distribution skewness is partially due to the geographic distribution of families of fishes and apparently enhanced by a nonrandom geographic distribution of species within families. These results are discussed in the context of previous explanations of factors responsible for the generation of species size-frequency distributions related to the fractal nature of the environment, energetics, and evolutionary patterns of body size in North American fishes.     

Mictic patterns of the rotifer Brachionus plicatilis Müller in small ponds

Populations of the rotifer Brachionus plicatilis were monitored in three small ponds in a marsh on the Mediterranean coast. Samples were taken approximately every three weeks from July 1992 to November 1993. Salinity, temperature, conductivity, pH and oxygen concentration were measured in the field. Population density was determined from preserved quantitative samples. Individuals were classified as mictic females, amictic females, non-ovigerous females, and males, differentiating between two morphotypes (S and L). From these counts, a level of mixis was calculated. We also determined the proportion of mictic females in natural populations by culturing females isolated from fresh samples. From these data, mictic patterns over time and correlation between levels of mixis and environmental and population parameters were analyzed. From a previous study S and L morphotypes were known to correspond to genetically different clonal groups. Our data showed that reproduction was predominantly parthenogenetic in these clonal groups, but mictic females were found in most samples, the proportion of mictic females ranging from 0 to 29%. The clonal groups showed different patterns of mixis. L clonal group presented a continuous sexual reproductive pattern. In contrast, S clones showed a rather punctuated mictic pattern. A positive correlation between levels of sexual reproduction and population density was found for S and L groups. However, they differed in their density threshold for mictic reproduction. The adaptive meaning of these patterns and their implications in maintaining genetic diversity within and between populations are discussed.     

Extent of polyteny in the pericentric heterochromatin of polytene chromosomes of pseudonurse cells of otu (ovarian tumor) mutants of Drosophila melanogaster

In the polytene nuclei of germ-line cells (ovarian pseudonurse cells) of Drosophila melanogaster females mutant for otu ¹¹ (ovarian tumor), the pericentric heterochromatin is much more abundant than in somatic salivary gland cells. This is due to the degree of heterochromatin compaction (and consequently the level of underreplication) being lower in the nurse cells than in the salivary gland cells. The lower level of compaction probably results in a very low degree of position effect gene inactivation in the ovarian nurse cells.     

Nest predation is little affected by parental behaviour and nest site in two African Sylvia warblers

Parental behaviour and nest site are supposed to affect nest predation in birds. Few nest visits and high nest attentiveness are assumed to lead to low predation rates. Poorly concealed nests are thought to be more likely to be preyed upon than well concealed nests. Studies on the relationship between parental behaviour, nest site, and nest predation are rare and none have, so far, been conducted in the Afrotropics. We studied the effect of nest site, nest visitation rate, and nest attentiveness on the nest predation rate of the two tropical warblers Sylvia boehmi and Sylvia lugens in Kenya. Parental behaviour and predation on nests of 13 breeding pairs of both species were observed daily in two consecutive breeding seasons. In both species, parental activity at the nest was low [0.9 trips to the nest in 30 min during incubation, maximum 4.6 (S. boehmi) and 5.8 (S. lugens) trips to the nest in the nestling stage]. Predation rates in both species were high (Mayfield nest success 19.4 and 33.2%). Our analysis revealed only weak evidence for an effect of nest site, nest visitation rate, and nest attentiveness on the predation rate. It is suggested that smaller clutches of tropical in comparison to northern temperate birds result from lower feeding rates in tropical ecosystems with high predation rates (Skutchs hypothesis). The underlying mechanism could not be proven in this study.     

Cytotoxic potency of trialkyltins to C6 glioma cells <Emphasis Type="Italic">in vitro</Emphasis>: impact of exposure conditions

Because of a possible role of astrocytes in trialkyltin-induced neurotoxicity in vivo various studies have been performed using cultures of astrocytes or glioma cells in vitro. With respect to cytotoxic potencies of trialkyltins these studies gave rather divergent results. Therefore the aim of the present study was to clarify whether variations of experimental conditions could be responsible for the differences of the cytotoxic activities of trimethyltin (TMT), triethyltin (TET) and tributyltin (TBT). Experiments were performed with rat C6 glioma cells. Toxicity was determined by measuring the reduction of the cell protein content. Cultures of proliferating and growth-arrested cells did not differ in their sensitivity. Exposure duration (1–72 h) had a strong but differing influence on the cytotoxic potency of the trialkyltins. After short exposure times the potencies differed largely (TMT < TET < TBT), whereas they became more and more similar with increasing exposure duration. The potency–time relationships for TMT and TET could be described by the equation: EC₅₀ = k x t ^–n, while for TBT an incipient value (EC_50,) had to be included: EC₅₀ = EC ₅₀ + k x t ^–n. Addition of serum albumin to the culture medium decreased the cytotoxic potency of the trialkyltins. However, the impact of protein binding on their bioavailability was relatively low. The cytotoxic potency of the alkyltins was not dependent on the concentration of C6 cells. Taken together, neither differences in exposure conditions nor in the proliferative status of the cells are sufficient to account for the discrepancies in published results for trialkyltin cytotoxicity to astrocytes. Instead they may – at least partially – be explained by differing sensitivities of the endpoints used. Furthermore, C6 glioma cells respond considerably more sensitively to trialkytins than primary astrocytes, which questions their applicability as models for astrocyte toxicity.     

Genetic differentiation and hybridization between greater and lesser spotted eagles (Accipitriformes:Aquila clanga, A. pomarina)

Greater and lesser spotted eagles (Aquila clanga, A. pomarina) are two closely related forest eagles overlapping in breeding range in east-central Europe. In recent years a number of mixed pairs have been observed, some of which fledged hybrid young. Here we use mitochondrial (control region) DNA sequences and AFLP markers to estimate genetic differentiation and possible gene flow between these species. In a sample of 83 individuals (61 pomarina, 20 clanga, 2 F1-hybrids) we found 30 mitochondrial haplotypes which, in a phylogenetic network, formed two distinct clusters differing on average by 3.0% sequence divergence. The two species were significantly differentiated both at the mitochondrial and nuclear (AFLP) genetic level. However, five individuals with pomarina phenotype possessed clanga-type mtDNA, suggesting occasional gene flow. Surprisingly, AFLP markers indicated that these mismatched birds (originating from Germany, E Poland and Latvia) were genetically intermediate between the samples of individuals in which mtDNA haplotype and phenotype agreed. This indicates that mismatched birds were either F1 or recent back-cross hybrids. Mitochondrial introgression was asymmetrical (no pomarina haplotype found in clanga so far), which may be due to assortative mating by size. Gene flow of nuclear markers was estimated to be about ten times stronger than for mtDNA, indicating a sex-bias in hybrid fertility in accordance with Haldanes rule. Hybridization between the two species may be more frequent and may occur much further west than hitherto assumed. This is supported by the recent discovery of a mixed pair producing at least one fledgling in NE Germany.     

Field experiments on the optical orientation of pelagic rotifers

Avoidance of shore by pelagic rotifers is considered to be the result of an optical orientation. Field experiments show that the spatial light distribution in the shore region determines the preferred direction of migration. The behaviour of Eudiaptomus gracilis was tested in comparison to that of rotifers.This publication is dedicated to Pater Dr. Josef Donner on the occasion of his 70th birthday     

The giant neurone system in ophiuroids

Summary The radial nerve cords of members of the class Ophiuroidea consist of two parts, the ectoneural and the hyponeural tissues, which are separated by an acellular basal lamina. The hyponeural tissue is composed entirely of motor fibres. The cell bodies of the hyponeural neurones are arranged in ganglia, one to each segment of the arm, and each containing approximately one hundred cell bodies. Synaptic contact between the two tissues occurs across the basal lamina. Ultrastructural evidence shows that the majority of these synapses operate in the ectoneural to hyponeural direction. Three pairs of nerve bundles, each containing approximately thirty five large motor fibres arise from each ganglion and innervate the intervertebral muscles. The large motor fibres divide into a number of pre-terminal axons in the region in which the motor fibre enters the muscle block. The terminal axons run at right-angles across the muscle fibres and neuromuscular junctions are found at the points of contact between the two; each terminal axon makes contact with a large number of muscle fibres. The hyponeural axons also pass through the juxtaligamental tissue before they reach the muscle blocks and there is some evidence of synaptic contact with the juxtaligamental cells. The juxtaligamental tissue is thought to be associated with changes in the structural properties of the collagenous ligaments of the arm during arm autotomy (Wilkie 1979). Degeneration studies confirmed the layout of the hyponeural motor axons.     

Protein export elements from Lactococcus lactis

Summary Broad-host-range plasmids carrying -amylase or -lactamase reporter genes lacking a signal sequence were used to select export elements from Lactococcus lactis chromosomal DNA that could function as signal sequences. Fragments containing such elements were identified by their ability to direct the export of the reporter proteins in Escherichia coli. Several of the selected export elements were also active in Bacillus subtilis and L. lactis, although the efficiencies depended strongly on the host organism and reporter gene used. The export elements AL9 and BL1 were highly efficient in L. lactis in the expression and secretion of at least two heterologous proteins (Bacillus licheniformis -amylase and E. coli TEM--lactamase). AL9 even permitted growth of this organism on starch as the sole carbon source. Nucleotide sequence analysis of five selected fragments indicated that these encode oligopeptides with the major characteristics of typical signal peptides. The putative expression signals had a limited similarity to previously described expression signals for E. coli, B. subtilis and L. lactis. Differences in both expression and export efficiency are likely to underlie the host-specific effects.     

Morphological stability of Pimpinella anisum hairy root cultures and time-course study of their essential oils

The morphological stability of hairy root cultures of Pimpinella anisum was studied using cultures grown in four different media, both in darkness and under photoperiod conditions of 16 h light; they were first subcultured every eight days and then later on every three weeks. From the four media tested, the hairy root cultures grown in SH medium both in darkness and under photoperiod conditions showed a marked morphological stability with no de-differentiation or greening, when compared with the other culture systems. The time-course study of the essential oils, isolated by distillation-extraction and analysed by GC and GC-MS, showed only quantitative differences in the composition of the oils. A clear heterogeneity in the accumulation pattern was found with regard to the five dominant compounds (pregeijerene, geijerene, zingiberene, -bisabolene and trans-epoxypseudoisoeugenyl 2-methylbutyrate), i.e., those that appeared in a relative amount higher than 5% at least once during the time-course study of the oils from the eight culture systems.     

The role of ‘Norin 10’ dwarfing genes in photosynthetic and respiratory activity of wheat leaves

Summary A comparative analysis of eight cultivars of spring wheat (Triticum aestivum) classified by height as tall (T), semi-dwarf (D₁), dwarf (D₂) and very dwarf (D₃) was conducted to study their efficiency of oxygen exchange during photosynthesis and dark respiration. Two cultivars were included in each height group.Cultivars carrying Norin 10 dwarfing genes (D₁, D₂ and D₃) were found to have a significantly higher photosynthetic rate per unit leaf area than talls (T) that lack these genes. Among the Norin gene carriers, dwarf group (D₂) was most efficient, followed by very dwarf (D₃) and semi-dwarf (D₁).Photosynthetic rate and respiratory rate were found to have a positive relationship.     

Genetic variation at storage protein-coding loci of common wheat (cv ‘Chinese Spring’) induced by nitrosoethylurea and by the cultivation of immature embryos in vitro

Electrophoretic patterns of seed storage proteins, the high-molecular-weight glutenins and gliadins, were studied in 468 plants of the common wheat cultivar Chinese Spring regenerated from callus culture of immature embryos, in 115 plants grown from seeds treated with nitrosoethylurea and in 260 control plants. From 5 to 21 single grains were analysed from each plant. In these three groups, the frequency of inherited mutations causing the loss of all proteins controlled by a locus (null-mutations, probably caused by a chromosomal deficiency) was 0.69%, 2.07%, and 0.05% per locus (the differences were statistically significant), respectively, while that of mutations causing the loss of a single protein band was 0.11%, 0.33%, and 0.05%, respectively. The loss of all of the gliadins controlled by Gli-B1 or GH-B2 (mutations were probably caused by a deletion of satellites of the corresponding chromosomes), was significantly higher than the loss of gliadins controlled by genomes A and D. Gene mutations altering the electrophoretic mobility of a single protein band in the pattern were found only in the second group of plants (0.44%). Therefore, chemical mutagenesis which produced not only more mutations than cultivation of immature wheat embryos in vitro, but also a higher ratio of mutations that altered DNA sequences, can be considered as an easier and comparatively more promising way for obtaining new improved variants of loci controlling biochemical characteristics in wheat. Somaclonal variation, on the other hand, was probably mainly caused by chromosomal abnormalities and could therefore hardly be considered as a useful tool in wheat breeding.     

The wise use of wetlands: identifying development options for Ghana's coastal Ramsar sites

The Government of Ghana has recently declared five coastal wetlands to be Ramsar sites. This requires the wise use of wetlands of international importance for bird habitat, but does not preclude human habitation or ecologically friendly development. The sites are Muni-Pomadze, Densu Delta, Sakumo, Songor and Keta. An attempt was made to identify and assess a range of development options for initiation within the sites that would be compatible with the environmental concerns of Ramsar, while also being technically and economically viable and socially acceptable to the communities in the sites. The appraisal included developing a detailed understanding of the physical, biological, human and institutional resources of the areas, the land uses and prevailing livelihood systems of local people, and the pressures placed on the natural resources of the wetlands. Many of the developments nominated by stakeholders were rejected, but twenty topics passed the initial tests. These were considered in more detail using information collected for the study by national specialists. Most of the options were considered suitable for local level implementation by community groups or local entrepreneurs. Government assistance will be needed to ensure an enabling institutional framework for small-scale business development is provided.     

‘Phytoantibodies’: a general vector for the expression of immunoglobulin domains in transgenic plants

Sequences encoding the immunoglobulin heavy-chain variable (VH) domains were engineered in a new general purpose vector to transform plants via Agrobacterium. The expression of an isolated VH domain (IVD) after introduction into the plant genome has been monitored by northern, western and immuno-histochemical analysis. Immunoblotting showed that the polypeptide was stably expressed and accounted for up to 1% of the soluble protein fraction. It is therefore proposed that single immunoglobulin domains of suitable specificity expressed in plants may constitute an effective system to inhibit the activity of molecules involved in plant pathology or plant development.     

Are biodiversity ‘hotspots’ correlated with current ecoclimatic stability? A pilot study using the NOAA-AVHRR remote sensing data

The GAC (Global Area Coverage) by the NOAA-AVHRR satellites represents an excellent data set for studying global and regional patterns of variations in surface conditions driven in part by climatic variation. In this pilot study we examined whether biodiversity hotspots, defined from peak concentrations of neoendemics as well as geographically relict forms, differ in ecoclimatic stability from surrounding areas under present-day climatic conditions. Coefficients of variation of the ratio between brightness surface temperature (Ts) and the Normalized Difference Vegetation Index (NDVI) based upon 10 years' monthly composited scenes of tropical Africa revealed distinctive geographical patterns of interannual variability in surface conditions. Regions with a predominance of old species are characterized by spatial uniformity in the ecoclimatic variability, while regions where rapidly radiating groups dominate are spatially complex in this respect. However, the exact hotspots, with peak concentrations of endemic species, are characterized by a local reduction in ecoclimatic variability, or placement on the boundary to a stable region. This relationship was supported statistically by comparing ecoclimatic profiles across montane forests representing hotspots, and those of other montane forests. It is suggested that, because of interactions between prevailing atmospheric flows, topography and vegetation, the impact of extreme weather is moderated locally. The correlation between current stability and aggregates of neoendemics as well as old relics indicate that local moderation of climatic extremes persist through shifting climatic periods, permitting populations of unique species to survive in these places. The results are used to identify study sites for better ground truthing and for paleoclimatological studies which may be useful for more thorough studies of these relationships.     

Amelanchier alnifolia vegetation in eastern Idaho,USA and its environmental relationships

Fifteen shrub stands of Amelanchier alnifolia vegetation were studied using Braun-Blanquet procedures, tabulated, and ordered by Twinspan, Decorana, and field experience into 5 groups of stands. The stands occurred on the lower slopes of the southwestern Teton and southeastern Big Hole mountains of eastern Idaho and in-and outside a U.S. Forest Service exclosure above the Hoback River in adjacent Wyoming. The ecology of this Amelanchier vegetation as a whole and of the 5 groups of stands is discussed using Jenny's factors of soil formation (1941, 1958, 1980) as a framework. Plant indicator values (Ellenberg 1979, 1988) which rank species on their occurrences in relation to light, temperature, continentality of climate, water availability, soil reaction (pH), and soil nitrogen supply, were independently assigned to the 121 species of vascular plants encountered in the described stands.     

Triaperturate pollen in the monocotyledons: configurations and conjectures

Triaperturate pollen are known in at least twenty seven genera of monocotyledons. Differences between aperture type and polarity indicate that the development of three apertures has occurred a number of times. Mode of cytokinesis during microsporogenesis is compared with differences in aperture configuration, to assess the extent to which this appears to influence aperture arrangement. Triapertury in monocot pollen tends to fall into one or another of three situations: 1) it is the normal state, 2) it is fairly common, but pollen with more or less apertures also occur in the taxon or sample, 3) it is a rare, or abnormal state for pollen which usually has less than three apertures. The various forms of triaperturate pollen are described, as well as monosulcate pollen of the orchid genera Cypripedium and Paphiopedilum, often misinterpreted as tri-sulcate, and the unusual extended trichotomosulcate pollen of Agrostocrinum (Hemerocallidaceae). Monosulcy, trichotomosulcy, and zonasulcy, with unusual and rare exceptions of zonasulcy in the eudicots, are aperture states shared exclusively with the basal dicots. Furthermore, to some extent all have links with the triaperturate condition in monocots and basal dicotyledons. This is discussed, as well as the association of tripory with polypory in monocots and basal dicots. The fossil pollen record is considered.This paper is dedicated to Klaus Kubitzki in recognition, not only for his extensive contribution to systematic botany, but also for his firm belief that pollen characteristics contribute to a better understanding of plant systematics and evolution.     

Mycoflora and aflatoxins in a West African corn-groundnut based convenience food

A total of 14 fungal species, mostly toxigenic, were isolated from 50 samples of donkwa snack obtained from 16 producers. All of the isolates recorded substantial growth, though at varying rates, on the 2% snack agar provided. They also induced a reduction in the oil and an increase in free fatty acids of the substrate suggesting their participatory roles in deterioration. Most of the snack samples analysed contained initial amounts of aflatoxins above the safe permissible level (30 ppb). The initial toxin levels increased substantially with storage time under 79.5, 89.5 and 100% ambient relative humidities but increased only slightly when samples were kept at 71% relative humidity. Almost constant toxin levels were recorded throughout the study period under 51% relative humidity. Accumulation of aflatoxin B₁ in samples was most enhanced at 89.5% relative humidity. Comparatively, greater amounts of aflatoxin B₁ accumulated under all conditions than the amounts recorded for aflatoxin G₁.     

Facile removal of the N-indole-mesitylenesulfonyl protecting group using HF cleavage conditions

Summary Nitrogen indole protection of the -methyltryptophan side-chain residue is important for avoiding undesired side reactions during peptide synthesis. Of great importance is the choice of a side-chain protecting group for orthogonal peptide synthesis and its stability under a variety of chemical conditions required for synthesis of the four isomers of this unusual amino acid. We report here the successful use of the mesitylenesulfonyl (Mts) protecting group for -methyltryptophan in the synthesis of melanotropin and CCK peptide analogues and the ready cleavage of this protecting group under HF conditions.