Temperature-induced changes in the life cycle of Leuctra nigra(Plecoptera: Leuctridae) from a Lake District stream

1. The life cycle of Leuctra nigra (Olivier) took 2 years in a small stream in the English Lake District and the exponential growth of the larvae was scarcely affected by variations in water temperature (range 4.2-14.0°C). Mean growth rates for three year-classes were 0.43±0.01, 0.42±0.01, 0.39±0.05% body length day^?1. There were thirteen or fourteen larval instars for males and fourteen or fifteen for females. The ratio between successive instars was a constant 1.20 (conformed with Dyar's rule). 2. Larval growth and mortality were exponential at six constant temperatures (5.9, 8.2, 12.1, 15.8, 18.2, 19.8°C) in the laboratory. Mean growth rates (% body length day^?1) increased directly with temperature from 0.37 (5.9°C) to 0.55 (19.8°C). Mean mortality rates (% day^?1) increased directly with temperature from 0.20 (5.9°C) to 0.26 (12.1°C) and then markedly increased to 0.54-0.58 at the three higher temperatures. Only 7-10% of animals completed their life cycle at the three higher temperatures compared with 23–27% at the three lower temperatures. Egg production also decreased considerably at the higher temperatures. 3. As growth rates in the stream and laboratory were similar at similar temperatures (<14°C), the optimum conditions for growth in the laboratory were probably similar to those in the stream; therefore resources such as food and space were not restricting growth in the stream. 4. The implications of the temperature-induced changes in growth and mortality are discussed and it is concluded that although the life cycle can change from semivoltine to univoltine with increasing temperature, the costs of a univoltine life cycle are high in terms of survival and egg production, both of which decreased markedly between 12.1 and 15.8°C. Therefore the optimum habitat for this species appears to be a summer cool stream (maximum temperature <14°C) and the optimal life cycle appears to be about 2 years from egg to adult.     

Biochemical and Ultrastructural Changes in Tetrahymena pyriformis During Starvation*

SYNOPSIS. Certain of the ultrastructural and biochemical changes occurring during the first 25 hr of starvation in Tetrahymena pyriformis were studied. Ultrastructurally, numerous profiles of degenerating mitochondria were seen in the early stages of starvation. The presence of oxidizable substrate such as glucose and acetate did not prevent this degeneration. Numerous large nucleoli were formed, many of which seemed to be passing into the cytoplasm as forming autophagic vacuoles. There was a transient increase in Oil Red O-positive bodies, presumably lipid (triglycerides). The extent and duration of this increase were pronounced in the presence of acetate. The lipid droplets appeared to arise within the cisternae of the endoplasmic reticulum. Lipid reserves were apparently utilized prior to carbohydrates, as the disappearance of lipid droplets preceded glycogen utilization, both in the presence of acetate and in the absence of exogenous substrate. A considerable loss of cellular protein also occurred. In cells from inorganic medium supplemented with glucose, glycogen occupied much of the cell, leaving only islands of cell organelles. Acid phosphatase was localized, ultrastructurally, mainly in autophagic vacuoles which contained mitochondria and other cell organelles, and in association with small, double-membraned structures which seemed to be sequestering small areas of cytoplasm. Such sequestered areas also appeared within larger autophagic vacuoles. Residual bodies containing concentric whorls of myelin-like membranes surrounding a more solid core accumulated during starvation. Acid phosphatase activity decreased in amount but not in specific activity. The specific activity of cathespin doubled or tripled, but there was little change in total enzyme.     

THE SOIL FUNGI OF THE DOVEY SALT MARSHES

In this investigation of the fungi of the soil of the Dovey Salt Marshes (Ynyslas) 48 fungi were isolated.
Twelve of the species found do not appear to have been recorded before for the British Isles.
The area investigated is a badly aerated, stiff, tenacious clay, alkaline in reaction ( p H 8), with a high water content, due mainly to periodical inundations by tidal salt water.
Method of investigation consisted in taking samples of soil from a depth of 11/2 and 31/2 inches and either planting portions of this directly on to specially prepared media, or first shaking up a portion in water and then inoculating the prepared media with some of the suspension.
Three fungi– Torula allii, Penicillium hyphomycetis and Fusarium oxysporium var. resupinatum —were almost invariably present in every sample of soil: almost equally common were Trichoderma lignorum, T. Köningi, Hormodendron cladosporoides, Mucor circinelloides and Periconia felina .
Most of the fungi found are species found above ground as saprophytes, and may have been introduced into the soil by drainage, etc.
The writer considers fungi are active only in association with organic material.
The vegetation covering this marsh shows marked zonation: soil samples were chiefly taken from the Glycerietum and Aimerietum.
The same species of fungi were common to the two associations.
Glyceria maritima is a most effective silt binder, because the stele of its rhizomes and roots consists almost entirely of lignified tissue which does not yield to the activities of the soil fungi; Armeria maritima is not so effective a silt binder because the stele of its rhizomes and roots contains very little lignified tissue—at a depth of a foot, the tap roots of Armeria are little more than hollow tubes, the interiors having been removed by fungi and bacteria.     

The Distribution of Tetrahymena pyriformis1

SYNOPSIS. This paper is a brief account of both amicronucleate and sexually active strains of Tetrahymena pyriformis and their distribution with some comments on their possible evolution.