Comparison of FDR- and SDR-derived tetraploid progeny from 2x×4x crosses using haploids of Solanum tuberosum L. that produce mixed modes of 2n eggs

 The relationship between heterozygosity and heterosis in tetraploid potato (Solanum tuberosum subsp. tuberosum L., 2n=4x=48) was examined in a series of first-division restitution (FDR)- and second-division restitution (SDR)-derived tetraploid subpopulations. The subpopulations were constructed using two 2n egg-producing, mixed-mode haploids (2n=2x=24) crossed to three tetraploid (2x= 4x=48) potato clones. Half-tetrad analysis using a co-dominant electrophoretic marker (Pgm-2), which is closely linked to the centromere, discriminated between FDR- and SDR-derived 4x progeny. The FDR:SDR ratio of the 4x progeny observed was dependent upon the haploid parent used in the 2x×4x cross. Field studies were conducted between 1992 and 1996 to compare the yield and specific gravity of the two subpopulations and their parents from three crosses. There was no difference in the total tuber yield or specific gravity between the FDR- and SDR-subpopulations based upon family means, despite the expectation that FDR-derived progeny would transmit a greater portion of the genome’s heterozygosity intact than SDR-derived progeny. The 4x parent in each family had a higher yield than either 4x progeny subpopulation. Inbreeding, as a consequence of the haploidization process and a lack of genetic diversity, may have negated any advantage of the FDR-derived progenies over the SDR-derived progenies. Received: 14 April 1998 / Accepted: 12 May 1998     

A new pressure sensory mechanism for prey detection in birds: the use of principles of seabed dynamics?

We demonstrate a novel mechanism for prey detection in birds. Red knots (Calidris canutus), sandpipers that occur worldwide in coastal intertidal areas, are able to detect their favourite hard-shelled prey even when buried in sand beyond the reach of their bills. In operant conditioning experiments designed to find out whether the birds could tell buckets containing only wet sand from buckets containing hard objects in wet sand, we show that they detect the presence not only of deeply buried live bivalves but also of stones. The latter finding virtually excludes, under experimental conditions, prey-detection mechanisms based on vision, acoustics, smell, taste, vibrational signals emitted by prey, temperature gradients and electromagnetic fields. A failure to discriminate between food and non-food trays with dry sand indicates that pore water is involved. Based on the presence of large arrays of Herbst corpuscles (sensory organs that can measure the acceleration due to changes in pressure), the specifics of foraging technique and the characteristics of sediments on which red knots feed, we deduce that the sensory mechanism involves the perception of pressure gradients that are formed when bills probe in soft sediments in which inanimate objects block pore water flow. To our knowledge, this mechanism has not been described before. It is argued that repeated probing in soft, wet sediments allows red knots to induce a residual pressure build-up of sufficient strength to detect the pressure disturbance caused by a nearby object. The cyclic process of shaking loosely packed sand grains followed by gravitational settling into a closer packing, leads, owing to insufficient drainage of the sediment, to a locally increased pressure disturbance that is ''pumped up'' at each shake.     

Application of polymerase chain reaction (PCR) and TaqMan PCR techniques to the detection and identification of Rhodococcus coprophilus in faecal samples.

Rhodococcus coprophilus, a natural inhabitant of herbivore faeces, has been suggested as a good indicator of animal (as opposed to human) faecal contamination of aquatic environments. However, conventional detection methods limit its use for this as they require up to 21 days to obtain a result. In this paper an optimised method for extracting R. coprophilus DNA from faecal samples is described. PCR and 5'-nuclease (TaqMan) PCR methods were developed to allow the detection and enumeration of R. coprophilus in faecal samples within 2-3 days. Both PCR methods targeted the 16S rRNA gene, producing an amplicon of 443 bp which was specific for R. coprophilus. Sixty cells were required to produce an amplification product by conventional PCR, while as little as one cell was required for the TaqMan PCR method. The latter approach gave a linear quantitative response over at least four log units with both bacterial cells and DNA. Successful amplification by PCR was achieved using DNA extracted from cow, sheep, horse and deer faeces but was negative for samples from humans, pig, possum, duck and rabbit. These PCR methods enhance the feasibility of using R. coprophilus to distinguish faecal pollution of farmed herbivores from human pollution.     

SIGNAL POLYMORPHISM IN THE WEB-DECORATING SPIDER ARGIOPE ARGENTATA IS CORRELATED WITH REDUCED SURVIVORSHIP AND THE PRESENCE OF STINGLESS BEES, ITS PRIMARY PREY

Abstract.— Many spiders, and in particular those in the genus Argiope, spin highly visible web decorations whose function and significance are the subject of spirited debate. In this work, we present data to address two of the competing hypotheses that fuel this controversy. In particular, we examine the relationship between the presence of web decorations and spider survivorship (predator‐protection hypothesis) and the relationship between the presence of prey and spider decorating behavior (the prey‐attraction hypothesis). Our laboratory studies reveal that the decorating behavior of the spider A. argentata has a genetic component but that the expression of decorating behavior tends to be elicited only when a spider is well fed. Furthermore, our field studies show that in the presence of abundant stingless bees, spider decorating behavior is induced. Nevertheless, our field surveys also suggest that spiders that decorate their webs show reduced survivorship. We propose that the high correlation between web decorating in the presence of stingless bees supports the hypothesis that A. argentata engage in decorating behavior when attracting or targeting specific prey types. However, we also propose that web decorations attract the predators of A. argentata because high‐frequency decorators suffer lower survivorship than spiders that decorate moderately or rarely. These findings suggest that spider web decorating behavior is affected by conflicting selection pressures: the positive effect of prey attraction versus the negative effect of predator attraction. Due to the heritable component of decorating behavior, web decorating among A. argentata is likely to be particularly sensitive to the spider's local ecology as well as local patterns of gene flow.     

Optimization of isolation and storage of sperm cells from pollen of perennial ryegrass (Lolium perenne L.)

Summary A procedure for isolating sperm cells of perennial ryegrass (Lolium perenne L.) was developed. The sperm cells were released from the pollen grains by osmotic shock, with the right combination of pH and osmolality being important for optimal release. Various combinations of vitamins E, C and fetal calf serum were tested with the aim of improving yield and long-term viability, and their possible mode of action as important components for improvement of these two parameters is discussed. Under optimized conditions, a yield of 12% was established, and the storage time after which 50% of the sperm cells were still viable was improved to 60 h. Cytological observations demonstrated that sperm cells of perennial ryegrass are true protoplasts, which may allow future fusion experiments to be carried out.     

Histological analysis of IL-2 induced regression of murine solid SL2-tumors

When DBA/2 mice are inoculated both intraperitoneally (i.p.) and subcutaneously (s.c.) with syngeneic SL2 lymphoma cells and treated i.p. on day 10–14 with 20,000 units IL-2/day, about 50% of the mice reject both the ascitic tumour and the s.c. tumour. During IL-2 therapy large areas of necrosis appear in the solid SL2 tumours between day 12 and 15. Immunohistochemical studies show that only a small number of infiltrating cells is present in the tumours. The percentage of macrophages (MHC-II⁺)in the tumours is about 1 and the percentage of T-lymphocytes (-TCR⁺) about 0.5. No differences in the numbers of infiltrating cells are seen in untreated and IL-2 treated tumour bearing mice. The tumoursurrounding infiltrate consists mainly of mononuclear cells: about 50% macrophages, 20% CD8⁺ cells, and 15% CD4⁺ cells. No tumour-infiltrating cells were found that express the IL-2 receptor.We conclude that direct cytotoxic activity of tumour infiltrating cells cannot account for the rapid occurrence of necrosis.When L3T4⁺ cells were eliminated by treating the mice with-L3T4 monoclonal antibodies before tumor inoculation and treatment with rIL-2, tumor eradication did not occur. So, L3T4⁺ helper T-cells are essential for IL-2-mediated tumour regression. Exogenous rIL-2 is not directly responsible for the induced tumour regression. A significant stagnation of intratumoural bloodflow is observed after histological analysis; yet it still needs to be determined whether this is the primary cause or consequence of the observed necrosis.Abbreviations BSA bovine serum albumin - CTL cytotoxic T-lymphocyte - FACS fluorescence activated cell sorter - HE haematoxylin and eosin - IFN interferon - IL-2 interleukin-2 - IL-2R interleukin-2 receptor - i.p. intraperitoneal(ly) - i.V. intravenous(ly) - LAK lymphokine-activated killer - MHC major histocompatibility complex - PBS phosphate buffered saline - s.c. subcutaneous(ly) - TCR T-cell receptor - TNF tumour necrosis factor     

Influence of management on the seed production and seed bank of calcareous fen species

Abstract. The dynamics of the seed production and seed bank of two dominant perennial species of calcareous fens were investigated in response to different mowing frequency, fallow or pasture. The production of fertile shoots responded strongly to management practices. On sites where mowing alternated with fallow, autumn mowing led to an increase of fertile shoot density in Schoenus ferrugineus and a decrease in Molinia caerulea in the subsequent season. Repeated annual mowing after long-term fallow raised the density in Schoenus and inhibited initiation of flowering shoots in Molinia. Seed set and viability were influenced mainly by climatic or other factors. Variation of seed production between sites and in consecutive years at the same site could thus be large. The relationship between total seed production and seed bank was weak, but it improved when germination rates were included in the calculation. As the seed bank was generally smaller than the viable seed production, low survival and a high turnover of seeds in the upper soil layers is assumed for both species. Implications for recruitment strategies are discussed.     

Magnetic relaxation analysis of dynamic processes in macromolecules in the pico- to microsecond range.

A formalism based on the theory of Markov processes and suitable for the analysis of multiple internal motions in macromolecules is presented. Computer calculations of specific motional models for (13)C nuclear magnetic resonance (NMR) relaxation, treated as special cases of the proposed formalism, demonstrate the potential of this approach for discriminating between different motional models on the basis of NMR relaxation data.