The ecological significance of resting sites and the seasonal habitat change in polecats (Mustela putorius)

The daytime resting sites of 13 radio-tracked polecats ( Mustela putorius ) were recorded in a mountainous and a lowland study area in Switzerland. Information on breeding sites was collected from questionnaires distributed throughout the country. At all resting sites, the polecats were completely invisible from more than a metre distant. During summer, when polecats mainly live in forests, individuals used many different hiding-places (e.g. small self-dug burrows, woodpiles, heaps of branches and dry leaves, dense vegetation). Such places were used for short periods, and then abandoned. Above ground, the polecats sometimes built nests of dry grass or moss. In winter, the polecats slept mainly inside barns, stables and other buildings. These resting sites were changed less frequently. In rainy weather throughout the year, subterranean places were preferred. Breeding polecats were often found inside houses, and obviously did not avoid human presence.
The importance of different types of resting sites for polecats is discussed. In summer, the quality of a resting place is of less importance than its distance from the foraging area, but in winter, warm resting places are essential and buildings are therefore considered an important resource for polecats in Switzerland. The seasonal habitat change can more readily be explained as a consequence of thermoregulatory problems than of food availability, and the distribution of polecats in Switzerland may be affected by the availability of suitable winter resting places. The northern limit of polecat distribution and its historical changes can be explained by the changing availability of human buildings which provide winter resting sites.     

Chemical Composition of the Epidermal, Hypodermal, Endodermal and Intervening Cortical Cell Walls of Various Plant Roots

A survey of chemical modifications in the cells of the epidermis,hypodermis, cortical parenchyma and endodermis in roots of 27plant species was performed. Cortical parenchyma walls weregenerally free of modifying substances whereas the walls ofthe epidermis, hypodermis and endodermis were usually modifiedby the presence of lipids, phenols, suberin or lignin. In mostcases, wall-modifying components could be detected within 5mm of the root apex. lipids, phenols, suberin, lignin, ferulic acid, root, epidermis, hypodermis, cortex, endodermis, cell wall     

Photosensitivity of Chromatophores

Almost all major phyla of invertebrates and lower vertebratesdisplay a direct sensitivity of their chromatophores to lightby either dispersing or—in rare cases—aggregatingthe pigment granules within the cell. This "primary response"of color change is an accessory component of the "dermal lightsense" and characterizes the chromatophores as an independentreceptor for light and effector of the chromomotor response.Photosensitivity does not seem to be restricted to certain partsof the pigment cell but is rather supposed to be a ubiquitousproperty of the chromatophore. Experiments on partially illuminatedchromatophores show that the photopigment, whose chemical compositionis still unknown, is localised within the plasma membrane orthe cytoplasmic ground substance. Threshold responses for ajust visible reaction are much higher than for background responsesand have for some pigment cells been determined to be in a rangebetween 0.2 and 0.5 erg/sec/cm². The physiological significanceof the photosensory reaction is closely related with thermoregulationand the protection of underlying tissue against harmful radiation.The chain of events involved in photosensory transduction remainsto be further studied and can at present be interpreted onlyon the basis of related phenomena like retinal pigment migrationand the light-sensitivity of simple non-pigmented contractilesystems.     

Filamentous Proteins from Plant Sieve Tubes

PROTEIN filaments are characteristic structural components of the assimilatory conducting elements of angiosperm plants (“P protein” of Cronshaw and Esau¹). We have isolated filamentous structures from the phloem exudate of cut cucurbit stems². The presence of the filaments could be clearly demonstrated after negative staining with the electron microscope.     

Synthesis of Acetylcholine in the Absence of Exogenous Choline

THE breakdown of acetyl-CoA during incubation with rat brain homogenate or sections of rat nervous tissue in the absence of choline has been reported by Kasa, Mann and Hebb¹. They found that the conversion of ¹⁴C-acetyl-CoA to ¹⁴C-acetate thus incubated was considerably depressed by 10^?4 eserine or 10^?5 M di-isopropylfluorophosphate (DFP) but further depressed by 10^?3 M DFP. Experiments in our laboratories lead us to offer an explanation for that part of the breakdown inhibited by eserine or low concentrations of DFP.     

Aerobic Metabolism of Brochothrix thermosphacta Growing on Meat Surfaces and in Laboratory Media

Acetoin and acetic, isobutyric and isovaleric acids are major end-products, and important components of the spoilage odours, of Brochothrix thermosphacta growing aerobically on meat surfaces or in tryptone-based medium containing glucose, ribose or glycerol. Acetoin and acetic acid are probably derived entirely from the carbohydrates and isobutyric and isovaleric acids from valine and leucine respectively. Glucose and pH are both important factors in controlling the relative amounts of end-products, low glucose and near neutral pH favouring fatty acid formation, high glucose and lower pH values favouring acetoin formation.     

Molecular Basis for Repressor Activity of Qβ Replicase

WITH the purification and characterization of viral replicases, a novel feature of nucleic acid polymerases—stringent template specificity—was recognized^1,2. Qβ replicase, the most extensively studied viral RNA polymerase^2–8, is now known to replicate Qβ RNA², the complementary Qβ minus strand⁹, RNA molecules described as “variants” of Qβ RNA^10,11 and a set of small RNAs of unknown origin which accumulate in Qβ-infected Escherichia coli, collectively designated as “6S RNA”¹². On the other hand, the RNA from phages related distantly, if at all, to Qβ^13,14, such as MS2 or R17 and of other viruses such as TMV² or AMV (Diggelmann and Weissmann, unpublished results) are completely inert as templates, as are ribosomal and tRNA from E. coli². Poly C and C-rich synthetic copolymers at high concentrations elicit synthesis which, however, remains restricted to the formation of a strand complementary to the template^15,16.     

Ribosomal RNA Turnover in Contact Inhibited Cells

CONTACT inhibition of animal cell growth is accompanied by a decreased rate of incorporation of nucleosides into RNA^1–3. Contact inhibited cells, however, transport exogenously-supplied nucleosides more slowly than do rapidly growing cells^4,5, suggesting that the rate of incorporation of isotopically labelled precursors into total cellular RNA may be a poor measure of the absolute rate of RNA synthesis by these cells. Recently, Emerson⁶ determined the actual rates of synthesis of ribosomal RNA (rRNA) and of the rapidly labelled heterogeneous species (HnRNA) by labelling with ³H-adenosine and measuring both the specific activity of the ATP pool and the rate of incorporation of isotope into the various RNA species. He concluded that contact inhibited cells synthesize ribosomal precursor RNA two to four times more slowly than do rapidly growing cells, but that there is little if any reduction in the instantaneous rate of synthesis of HnRNA by the non-growing cells. We have independently reached the same conclusion from simultaneous measurements on the specific radioactivity of the UTP pool and the rate of ³H-uridine incorporation into RNAs (unpublished work of Edlin and myself). However, although synthesis of the 45S precursor to ribosomal RNA is reduced two to four times in contact inhibited cells, the rate of cell multiplication and the rate of rRNA accumulation are reduced ten times. This suggests either “wastage”⁷ of newly synthesized 45S rRNA precursor, or turnover of ribosomes in contact inhibited cells Two lines of evidence suggest that “wastage” of 45S RNA does not play a significant role in this system. (1) The rate of synthesis of 45S RNA in both growing and contact inhibited cells agrees well with that expected from the observed rates of synthesis of 28S and 18S RNAs (unpublished work of Edlin and myself). Emerson has made similar calculations⁶. (2) 45S RNA labelled with a 20 min pulse of ³H-uridine is converted in the presence of actinomycin D to 28S and 18S RNAs with the same efficiency (approximately 50%) in both growing and contact inhibited cells. These results indicate that, in order to maintain a balanced complement of ribosomal RNAs, contact inhibited cells must turn over their ribosomes. We present evidence here that rRNA is stable in rapidly growing chick cells, but begins to turn over with a half-life of approximately 35–45 h as cells approach confluence and become contact inhibited.     

Influence of Photoperiod, Daylength, and Feeding Schedule on Tadpole Growth and Development

The metamorphic rate of Rana pipiens tadpoles was studied under different photoperiods, daylengths, and feeding schedules. Tail resorption and hindlimb growth and development induced by immersion in 30 μg/l thyroxine (T₄) were accelerated under longer photoperiods and continuous light when 6L: 18D, 12L: 12D, 18L: 6D, and 24L regimes were compared. Constant light exposure did not produce faster development than an 18 hr photoperiod, and initially was less effective. The rate of spontaneous and T₄-induced metamorphosis was greater the shorter the day on 9L:9D, 12L: 12D, or 15L: 15D cycles, although all groups received the same overall amount of light, but in different dosages. When feeding schedule but not the LD cycle was varied, groups of tadpoles fed on 18, 24, or 30 hr regimes showed no differences in growth and development rate on 19L: 5D, and only random variations under continuous light. Differences in metamorphic rate on 18, 24, or 30 hr days are not due to the feeding schedules, but to the LD cycles. From these experiments we conclude that illumination, particularly the length and frequency of the photoperiod, affects the utilization of T₄. Development rates independent of the total amount of illumination, but related to daylength and light schedule, suggest interaction of light with an endogenous timing mechanism.