Cytochemistry and Ultrastructure of Hyphae and Haustoria of Peronospora parasitica (Pers. ex Fr.) Fr.

The uniform distribution of nuclei, mitochondria, lipid material,protein, and RNA in the hyphae and haustoria of Peronosporaparasitica was demonstrated by staining techniques. Glycogenwas not detected, the only insoluble carbohydrate material detectedby the periodic acid-Schiff reaction being in the fungal wall.The host cell walls reacted more intensely to this stain thanthe hyphal walls. The reaction of haustorial walls varied betweenthe slight staining reaction characteristic of the fungal walls,and the strong reaction of the host cell wall. Callose sheathswere occasionally seen. Fine structure was found to be similar to that of other Oomycetes.Welldeveloped sheaths of a vesicular nature, possibly synonymouswith callose sheaths, were occasionally seen partly surroundinghaustoria.     

Some population consequences of variation in preference among individual predators

A number of foraging studies have demonstrated that populations of predators rarely consist of individuals with identical preferences for particular types of prey. Variation among predators can lead to frequency-dependent changes in population preference, because those predators mat prefer the rarer type of prey generally have the greatest influence on population preference. In this study we develop a series of theoretical models which demonstrate how anti-apostatic selection (i.e. selection against the rare form) can arise out of (a) bimodal and (b) normal variation in preference among individuals of the same species. We show that population level anti-apostatic selection can occur even when individual predators show pro-apostatic selection (i.e. selection against the common form). Furthermore, patterns of population prey selection that arise out of variation in preference can potentially be pro-apostatic over one range of relative densities and anti-apostatic over another range of relative densities. Finally, we examine a case study involving predation by female waterboatmen Notonecta glauca and show that the variation in preference in this species is large enough to generate higher anti-apostatic selection than would be expected from the diet selected by the average individual.     

Ultra-trace analysis of soluble zinc, cadmium, copper and lead in Windermere lake water using anodic stripping voltammetry and atomic absorption spectroscopy

SUMMARY. The concentrations of trace metals in filtered and unfiltered lake water were measured using anodic stripping voltammetry, before and after digestion by ultra-violet irradiation, and by atomic absorption spectroscopy with electrothermal atomization. Total soluble components were estimated to be: zinc, 2.1 μg 1⁻¹; cadmium, <0.05 μg l⁻¹; lead, <(0.1 μg l⁻¹ and copper, 0.3 μg 1⁻¹. Atomic absorption spectrophotometric results and u.v.-digested, anodic stripping voltammetric results were in good agreement. All measurable zinc was electrochemically labile whereas copper above the detection limit of 0.09 μg l⁻¹ was electrochemically inert.     

UPTAKE AND RELEASE OF TAURINE FROM CEREBRAL CORTEX SLICES AND THEIR SUBCELLULAR COMPARTMENTS

—Cortex slices, synaptosomes and C-6 glioma cells were used to study [³⁵S]taurine uptake and its electrically-stimulated release. After exposure to taurine at two concentrations, the synaptosome preparation subsequently derived from the slices contained 41% of the particle-bound taurine and 16% of the total in the tissue. The uptake of [¹⁴C]GABA by C-6 glioma cells was inhibited 3-fold more by β-alanine than by l -DABA, whilst synaptosome preparations showed the opposite pattern, l -DABA being 2 or 3 times more effective than β-alanine. [³⁵S]Taurine uptake inhibition by l -DABA was low for synaptosomes and C-6 glioma, whereas β-alanine showed considerable effect on C-6 glioma (41%) and slices of white matter (ependyma; 50%). Synaptosome preparations showed little effect with β-alanine. When 30 min rather than 5 min incubations were employed, β-alanine depressed [³⁵S]taurine uptake by cortex slices by 30%. Taurine was taken up by a calcium-dependent mechanism and subcellular fractionation indicated that the synaptosome fraction showed losses commensurate with the net taurine release when low stimulation currents were used.     

An East–West distribution of divergent mitochondrial haplotypes in British populations of the land snail, Cepaea nemoralis (Pulmonata)

Some continental European populations of the land snail Cepaea nemoralis have mitochondrial haplotypes that differ by up to 20% at the 16S rRNA locus. I mapped the distribution of different lineages in populations from 36 different sites in Britain and Ireland. In 93% of individuals, one of two mitochondrial lineages was found, A or. N , which differ from each other by about 6% using a 16S rRNA fragment {approximately 300 base pairs). The distribution of these two types is very striking–one is confined to Wales, West and central England, and Scotland, while the other is found mainly in East and central England. The two types meet in a transition zone. The most likely explanation for the distribution is that it reflects two routes of colonization after the last ice age. Cepaea dispersal is leptokurtic, and only limited gene flow occurs between established populations, so that the original pattern could have been retained since the post-glacial colonization. However, many environmental gradients are orientated East-West, so alternative selective explanations are possible. A distinct mitochondrial lineage, as well as fossil evidence, suggests that Ireland was colonized separately from Britain. The implications of these distributions for the origins of the puzzling geographical patterns of shell types known as 'area effects' is discussed.     

Recruitment variation in a stream galaxiid fish: multiple influences on fry dynamics in a heterogeneous environment

1. The relative importance of density‐dependent and density‐independent processes in explaining fluctuations in natural populations has been widely debated. In particular, the importance of larval supply and whether it may control the type of regulatory processes a population experiences has proved contentious. 2. Using surveys and field experiments conducted in streams in Canterbury, New Zealand, we investigated how variation in the survival of non‐migratory Galaxias vulgaris fry was affected by density‐dependent and density‐independent processes and how this variation influenced recruitment dynamics. 3. Fry populations with high settlement densities experienced a 70–80% reduction in population size from density‐related mortality during the first fourteen days after peak settlement but thereafter the influence of density‐dependent processes on fry was weak. The impact of environmental conditions on fry populations was dependent on fry size and the magnitude of the perturbation, such that flooding effects on fry survival were most severe when fry were small. 4. In streams not affected by flooding, the size and density of introduced trout (Salmo trutta and Oncorhynchus mykiss) were the most significant factors determining the abundance of eventual recruits. A field experiment manipulating brown trout access to fry populations revealed that trout as small as 110 mm may be capable of greatly reducing and possibly preventing galaxiid recruitment. 5. Overall, the results indicated density‐dependent population regulation was only possible at sites with high native fish densities because trout were likely to be suppressing the number of potential recruits at sites with low native fish numbers. Whilst density‐dependent processes had a strong effect on fry survival following the period of peak fry abundance, density‐independent processes associated with flow and predatory trout influences on fry survival largely determined recruitment variability among galaxiid populations. Focusing conservation efforts on improving habitat to increase fry retention and reducing the impacts of trout on galaxiids would ensure more native fish populations reached their potential abundance.