Temporal scale, phytoplankton ecology and palaeolimnology

1. Scales of temporal analysis in limnology generally cover dial through to interannual changes, with occasional longer studies with up to 50 years continuous sampling data. Lakes, however, have been changing over much longer time periods than this, as is apparent from palaeolimnological studies. Temporal scales are, however, largely relative, with an individual's perspective controlling what is deemed short or long term. 2. Phytoplankton populations are variable over a variety of timescales, and the sediment record can readily record these changes from interannual through to 10³-year timescales. Because of anthropogenic influences, such as acidification and eutrophication, phytoplankton communities probably have been altered dramatically in many lakes, often before routine sampling began. Records of changing phytoplankton populations at timescales relevant to limnologists can be derived from, for example, varved sediments and used to address specific problems, such as the degree of long-term interannual variability and timescales of sexual reproduction. 3. Palaeolimnologists tend to interpret changes in sediment assemblages in terms of ecological and physiological processes which are relevant at scales that may not be resolvable in lake sediments. There is a clear need for sediment records to be interpreted in terms of the processes which operate at timescales that match the resolution of that sediment sequence. 4. Increasingly fine sampling resolutions are being attempted by palaeolimnologists, often without consideration of the reasons for such an approach or to the repeatability of the results. The increased variability associated with high-resolution sampling can make it difficult to separate noise from the ecological signal. There is a clear need for replication. 5. The necessary temporal resolution is defined by the aim of any given palaeolimnological study. If the main emphasis of a study is, for example, establishing background phosphorus concentrations, a coarser sampling resolution is probably acceptable than that required for many ‘ecological’studies.     

Light and Electron Microscopic Observations of Gametogenesis in Hastigerina pelagica (Foraminifera)*

SYNOPSIS. During gametogenesis mother individuals of Hastigerina pelagica (d'Orbigny) undergo significant morphological changes. Thirty h before gamete release, the cytoplasm changes from pale orange to bright red, possibly due to transport of stored lipids from the inner region to more peripheral parts of the cytoplasm. During the next 10 to 15 h the bubble capsule which surounds the calcareous shell is discarded. After all bubbles have disappeared, the individual sheds its spines by resorbing the spine bases close to the shell surface. A single mother nucleus divides into some hundreds of thousands of gamete nuclei within a span of ～ 20 h. A bulge of cytoplasm is extruded from the aperture and increases in size during the next 5 to 10 h. This bulge consists of cytoplasmic strands in which gametes and spherical bodies are embedded. The gametes and spherical bodies mature and are released during the afternoon and early evening. The gametes have 2 unequal acronematic flagella. A previously undescribed structure in foraminiferal reproduction is the spherical body which consists of a large vacuole surrounded by a thin cytoplasmic layer in which several nuclei, various typical cell organelles and multiple flagella are present. The spherical bodies are believed to play a role as receptacles of waste material, possibly including residual digestive enzymes, thereby protecting the gametes from lysis during the reproductive process. Fusion of gametes and further development into the next generation have not been observed.     

Effect of neurotensin on pancreatic function in man

The effect of neurotensin on submaximally-stimulated hepatobiliary and pancreatic secretion was studied in 6 healthy subjects. An intravenous infusion of neurotensin 1.4 ± 0.3 pmol/kg/min, designed to reproduce plasma neurotensin immunoreactivity levels within the physiological range, produced a significant increase in pancreatic bicarbonate output. Plasma concentrations of pancreatic polypeptide rose by 83 ± 16 pmol/l and were associated with a small reduction in trypsin, but no significant change in bilirubin outputs.     

Variations in the composition and properties of the gum exuded by Acacia karroo Hayne in different African locations*

The variation in chemical composition of 15 specimens of the gum exudate from Acacia karroo Hayne, obtained from four different African locations, has been investigated. The range of analytical values found (e.g., specific rotation + 36° to + 67°; uronic acid 10.3 to 18.1%; rhamnose 4 to 10%) reflect the well-known variability of this Acacia species. The major analytical difference concerns the unusually wide range of molecular weights observed, i.e., 1.5 × 10⁵ to 48 × 10⁵. The material of highest molecular weight, from trees infested with Cerambycid beetles, is consumed by bush-babies (Galagidae).     

A Rapid and Direct Plate Method for Enumerating Escherichia coli biotype I in Food

Direct enumeration of Escherichia coli biotype 1 in foods within 24 h has been achieved by a development of the method of Delaney, McCarthy & Grasso (1962) which is based on the production of indole at 44°. Indole positive E. coli growing at this temperature on a cellulose acetate membrane overlaying tryptone bile agar can be demonstrated. Characterization of 555 indole positive colonies from 843 samples of food showed that 95% were E. coli biotype 1 and a further 3·4% were 'faecal coliforms'. Anaerogenic and non-lactose fermenting E. coli are detected and the significance of these strains is discussed.