Hatching of Daphnia sexual eggs. I. Intraspecific differences in the hatching responses of D. magna eggs

• 1 To test the hypothesis that the variability in hatching response of the sexual eggs of Daphnia has a genetic component, hatching after a standardized decapsulation technique was studied in different D. magna families, resulting from intra- as well as interclonal crosses.
• 2 There were significant differences in hatching response between families. Average hatching rates ranged from 0.0% to 81.9%, depending on the family under study.
• 3 Offspring-on-parent regressions indicate that the hatching rate-of sexual eggs is to a large extent determined by the genotype of the mother (maternal inheritance).
• 4 Our results suggest that there is ample generic variation on a microgeographic scale for characteristics related to hatching of sexual eggs in Daphnia.

     

The Effect of Different Levels of N Limitation on Sugars, Amino Acids, Growth and Biomass Partitioning in Broadbean (Vicia faba L.)

Broadbean plants (Vicia faba L.) were submitted to three differentlevels of steady state N limitation. Relative addition ratesof N were 0.06, 0.1 and 0.14d^-1. Plants were harvested at fiveevenly distributed times over a 2d period. Shoot growth correspondedwell with the imposed treatment. Root growth, relative to shootgrowth, was highest at the 0.06d^-1treatment. Diurnal patternsof soluble sugars, amino acids and starch were analysed. Onaverage, soluble sugar levels were highest in the plants ofthe 0.06d^-1treatment whereas average free amino acid levelswere highest in the 0.14d^-1treatment. Shoot growth increasedas the concentration of shoot amino acids increased. No suchcorrelation however could be found between root growth and freesugar levels in the root. Broadbean; Vicia faba L.; exponential addition; N limitation; free sugar; amino acids; diurnal cycle; functional equilibrium; starch     

Size and shape distribution of level-bottom tabulate corals and stromatoporoids (Silurian)

Baarli, B. G., Johnson, M. E. & Keilen, H. B. 1992 07 15: Size and shape distribution of level-bottom tabulate corals and stromatoporoids (Silurian).
Size and shape distribution of tabulate coral and stromatoporoid faunas were studied at two Lower Silurian sections in Norway on the Baltic platform and one section in eastern Iowa on the Laurentian platform. All the sections are dominated by storm beds with predominantly shallowing upward features; they differ from one another in clastic content and proximity to land. Most of the fauna lived below normal wave-base, but within the photic zone, on fine grained and firm bottoms. In all three localities, size clearly increases up-section for stromatoporoids, favositids, and heliolitids but it decreases for halysitids in the Oslo region. Sediment influx worked negatively on size but generally not so much as to affect average size. lurbulence in combination with decreasing sediment influx affected the size decrease in heliolitids up section. Nutrients and turbidity were of minor importance as growth controlling factors. Light intensity is the only factor that shows a pattern consistent with increased size up-section. Sediment influx alfected fauna composition and shape: heliolitids had the highest sediment tolerance and stromatoporoids had the lowest. Ragged skeletons were linked to tempestites. Corals and stromatoporoids reveal a population-specific response to environmental change, largely independent of benthic assemblage zones or communities. Tabulate corals, stromaroporaids, bathymetry, size variation. clastic input, benthic assemblages .     

Development and mapping of a public reference set of SSR markers in Lolium perenne L.

We report on the characterization and mapping of 76 simple sequence repeat (SSR) markers for Lolium perenne. These markers are publicly available or obtained either from genomic libraries enriched for SSR motifs or L. perenne expressed sequence tag (EST) clones. Four L. perenne mapping populations were used to map the SSR markers. A consensus linkage map of the four mapping populations containing 65 of the SSR markers is presented, together with primer information and a quality score indicating the usefulness of the SSR marker in different populations. The SSR markers identified all seven L. perenne linkage groups.     

Nuclear magnetic resonance imaging in studies of gravitropism in soil mixtures

Gravitropic responses of oat coleoptiles were measured in different growth media; humid air, natural soil and artificial soil (glass beads). The oat coleoptiles in soil and glass beads were monitored by NMR imaging, while those in humid air were imaged in darkness with an infrared-sensitive charge-coupled device (CCD) camera. The present study shows for the first time that gravitropic experiments can be performed in artificial soil using NMR imaging as a convenient and suitable recording method. Not only was it possible to follow the gravitropic curvatures in natural soil, but the artificial soil allowed plant images of sufficient spatial and temporal resolution to be recorded. The advantages of using artificial soil in magnetic resonance imaging studies are that the iron content of glass beads is very low compared with natural soil, and that the artificial soil matrix can easily be standardized with regard to particle size distribution and nutrient content. Two types of glass beads were used, the diameter of the small and the large beads being 300–400 and 420–840 μm, respectively. The growth rate of the coleoptiles in soil and in big beads was roughly the same and only slightly lower than in humid air, whereas small beads reduced the growth rate by approx. 16%. The bending rate of the coleoptiles during the gravitropic response was reduced by c. 65% in soil and 75% in bead mixtures relative to bending in air. It should be noted, however, that the maximum curvature of the coleoptile tip was of the same order in all cases, about 35°. This value may represent the largest possible curvature of the organ. The potential of NMR imaging to study how plant organs penetrate the soil under the influence of gravitropism, mechanical impedance and thigmotropism is also discussed.     

Primers and polymerase chain reaction conditions for DNA barcoding teleost fish based on the mitochondrial cytochrome b and nuclear rhodopsin genes

This report describes a set of 21 polymerase chain reaction primers and amplification conditions developed to barcode practically any teleost fish species according to their mitochondrial cytochrome b and nuclear rhodopsin gene sequences. The method was successfully tested in more than 200 marine fish species comprising the main Actinopterygii family groups. When used in phylogenetic analyses, its combination of two genes with different evolutionary rates serves to identify fish at the species level. We provide a flow diagram indicating our validated polymerase chain reaction amplification conditions for barcoding and species identification applications as well as population structure or haplotyping analyses, adaptable to high‐throughput analyses.     

Hatching of Daphnia sexual eggs. II. The effect of age and a second stimulus

• 1 We examined the effect of age on the hatching response of Daphnia magna sexual eggs of specific families. For old eggs (>2 years), hatching characteristics were compared at two storage temperatures (4°C and 20°C). Also, the hatching response after a second dark incubation and subsequent incubation under conditions favourable for hatching was compared with that after the first stimulus.
• 2 Daphnia sexual eggs were found to remain viable for several (at least 4.5) years. The effect of age on the hatching rate was family dependent. At least in some families, hatching rate was higher for old (>2 years) than for young (<5 months) eggs. Low temperature (4°C) during dark incubation resulted in a higher hatching rate compared with incubation at 20°C.
• 3 The application of a second hatching stimulus resulted in a renewed hatching response. The overall hatching rate after the second stimulus was, however, lower than that of the first stimulus.
• 4 More than 80% of the hatchlings of young eggs appeared on Day 3 or 4, with minor between-family differences in time distribution of hatching. The timing of the response to hatching stimuli was more variable in old than in young eggs, with the average time at hatching being 6.4 instead of 4.0 days. The response to the application of hatching stimuli was also slower after the second stimulus compared with the first stimulus.

     

Genetic variability among root voles (Microtus oeconomus) from different geographic regions: populations can be distinguished by DNA fingerprinting

Genetic variability among root voles (Microtus oeconomus [Pallas, 1776]) originating from two distantly separate regions of Norway (Valdres and Finnmark) was studied by DNA fingerprinting using the probes 33.15, 33.6 and M13. All three probes revealed polymorphic, although relatively simple, patterns. DNA fingerprint banding patterns were clearly diagnostic of the animals' region of origin. Notably, Valdres animals display a high molecular-weight cluster of bands not found in Finnmark, reflective of the isolation, and possibly an indication of separate colonization events, of the two groups. On the local level in Finnmark, bands associating with a specific trap site were observed in trappings on consecutive years. Comparisons of Finnmark animals taken at three trap sites at approximately 10 km intervals show a gradient of genetic similarity. Captive bred siblings were also compared, yielding average values significantly higher than those seen from same-site comparisons. We suggest that the sensitivity provided by DNA fingerprinting with multi-locus minisatellite probes is appropriate for population genetic studies in M. oeconomus. Also, because band-sharing correlates to spacing in M. oeconomus, we propose that DNA fingerprinting may be used to study dispersal, recruitment and other population processes in this and possibly other rodent species.