BACTERIAL CHANGES IN EXPERIMENTAL LABORATORY SILAGE

SUMMARY: In preliminary experiments with grass silage made in the laboratory under controlled conditions bacterial numbers reached a peak earlier in silage held at 30° than at 22°, although maximum numbers tended to be greater at the lower temperature. Wilting the grass before it was ensiled delayed bacterial action, while chopping the grass hastened the action and helped to ensure a low pH in the silage.     

Activity and Compartmentation of Photosynthetic Carboxylases in Normal and Chloroplast-mutant Maize Leaves

The activity of ribulose-l,5-diphosphate carboxylase (RudiP-carboxylase) and phosphoenolpyruvate carboxylase (PEP-carboxylase) measured in vitro was independent from the chlorophyll content of the leaves. The relatively high activity of PEP-carboxylase as compared to the RudiP-carboxylase activity was particularly pronounced in the mutants. Realization of the potential (in vitro measured) carboxylating activities in fixation of CO₂in vivo was practically complete in normal leaves. In the mutants, however, CO₂ fixation was lower than the level permitted by the carboxylase activity. This could be explained only in part by the impaired rate of photophosphorylation. Compartmentation of PEP-carboxylase was different in normal and mutant leaves: in contrast to the normal ones, parenchyma-sheath cells of the mutants exhibited high PEP-carboxylase activity. Competition of PEP-carboxylase with RudiP-carboxylase for CO₂ in the mutants led to accumulation of organic acids, and can account for their low photosynthetic activity.     

Solute Accumulation by Grape Pericarp Cells: V. RELATIONSHIP TO BERRY SIZE AND THE EFFECTS OF DEFOLIATION

We have studied the accumulation of water, dry matter (DM) andglucose and fructose (G + F) in selected grape berries cv. Dolcettoof varying initial size growing on leafed and defoliated vines.The first measurements at 2 d after veraison were obtained non-destructivelyfrom correlations with linear dimensions and deformability;the final measurements were made when the berries were harvested13 d later. The increments in DM and G + F per pericarp increased with initialberry size thus discounting an hypothesis of an equal amountof solutes supplied to all berries. The increments in weightof DM and G + F per increment of pericarp volume were constantin berries of different size, supporting an hypothesis of acontrol determined by concentration in the solution availablefor accumulation in all berries. Defoliation reduced the incrementsper pericarp and per g fr. wt. by about the same proportionand its effects were consistent with the above interpretations. Key words: Grape pericarp, sugar accumulation, phloem unloading, Vitis vinifera.     

Host‐plant genotype mediates supply and demand of animal food in an omnivorous insect

1. Omnivorous predators can protect plants from herbivores, but may also consume plant material themselves. Omnivores and their purely herbivorous prey have previously been thought to respond similarly to host‐plant quality. However, different responses of omnivores and herbivores to their shared host plants may influence the fitness, trophic identity, and population dynamics of the omnivores. 2. The aim of the present study was to show that an omnivorous heteropteran (Anthocoris nemorum L.) and two strictly herbivorous prey species respond differently to different genotypes of their shared host plant, Salix. Some plant genotypes were sub‐optimal for the omnivore, although suitable for the herbivores, and vice versa. 3. The contrasting patterns of plant suitability for the omnivore and the herbivores highlight an interaction between plant genotype and omnivores' access to animal food. Plant genotypes that were sub‐optimal for the omnivore when herbivores were experimentally excluded became the best host plants when herbivores were present, as in the latter situation additional prey became available. By contrast, the quality of plant genotypes that were intrinsically suitable for omnivores, did not improve when herbivores were present as these plant genotypes were intrinsically sub‐optimal for herbivores, thus providing omnivores with almost no additional animal food. 4. The differential responses of omnivores and their prey to the same host‐plant genotypes should allow omnivores to colonise sub‐optimal host plants in their capacity as predators, and to colonise more suitable host plants in their capacity as herbivores. It may thus be difficult for Salix to escape herbivory entirely, as it will rarely be unsuitable for both omnivores and pure herbivores at the same time.     

Persistence and diversification of the Holarctic shrew,Sorex tundrensis (Family Soricidae), in response to climate change

Environmental processes govern demography, species movements, community turnover and diversification and yet in many respects these dynamics are still poorly understood at high latitudes. We investigate the combined effects of climate change and geography through time for a widespread Holarctic shrew, Sorex tundrensis. We include a comprehensive suite of closely related outgroup taxa and three independent loci to explore phylogeographic structure and historical demography. We then explore the implications of these findings for other members of boreal communities. The tundra shrew and its sister species, the Tien Shan shrew (Sorex asper), exhibit strong geographic population structure across Siberia and into Beringia illustrating local centres of endemism that correspond to Late Pleistocene refugia. Ecological niche predictions for both current and historical distributions indicate a model of persistence through time despite dramatic climate change. Species tree estimation under a coalescent process suggests that isolation between populations has been maintained across timeframes deeper than the periodicity of Pleistocene glacial cycling. That some species such as the tundra shrew have a history of persistence largely independent of changing climate, whereas other boreal species shifted their ranges in response to climate change, highlights the dynamic processes of community assembly at high latitudes.     

Risk‐taking and survival in the House Sparrow Passer domesticus: are plumage ornaments costly?

An important cost of sexual and social colour signals may be increased conspicuousness of the animals to visual predators. Although such predation costs have repeatedly been proposed for various ornaments of birds, especially for melanised and depigmented signals with low presumed production costs, tests of this hypothesis are rare and inconclusive. In this study we investigated whether individual variation in plumage ornamentation was associated with predator-related risk-taking behaviour and short-term survival in free-living House Sparrows Passer domesticus . In a large sample of birds we measured three aspects of coloration used in sexual and social signalling: the size of the melanised black throat patch in males, and the area and conspicuousness of the depigmented wing-bar in both sexes. We measured risk-taking by manipulating the distance of feeders from shelters, and recorded individually ringed birds feeding close to and far from shelter. Sparrows seemed to perceive the farther feeders as more risky, as indicated by the shorter time spent and smaller groups feeding far from rather than close to shelter. However, the use of the more risky (farther) feeders was not related to any of the colour traits we measured, suggesting that Sparrows do not adjust their risk-taking behaviour to their ornamentation. Males (the more ornamented sex) did not take less risk than females. Furthermore, we found no evidence that larger throat patches or more ornamented wing-bars reduced the probability of survival. Our findings were robust and consistent across multiple approaches, even when we controlled for several potential confounding effects. These results do not support the suggestion that melanised and depigmented plumage ornaments have significant predation costs in House Sparrows.