Mechanisms of inhibition of Erwinia amylovora by Erw. herbicola in vitro and in vivo

The mechanisms by which Erwinia herbicola inhibits Erwinia amylovora , the fire blight pathogen, were investigated. The optimum pH for growth of Erw. amylovora strain Ea273 in nutrient-yeast extract-glucose broth (NYGB) was 7.0 and growth was markedly reduced at pH values below 6.0. In contrast, the growth rates of Erw. herbicola strains Eh141 and Eh112Y were only slightly reduced at pH levels as low as 4.5, relative to pH 6-8. When Ea273 was grown in NYGB in the presence of Eh141 or Eh112Y, the media became acidic and lower populations of Ea273 were recovered, compared with populations from buffered NYGB. Acidification of plant tissue as a consequence of growth of Erw. herbicola did not occur, however, and thus acid-based inhibition of growth in planta is unlikely. The growth rates of nine strains of Erw. herbicola and their abilities to reduce the pH of NYGB did not correlate with their different abilities to prevent development of fire blight incited by Ea273 in a research apple orchard. When grown in mixed culture, Eh114 and Eh112Y grew to higher populations than Ea273 due to depletion of a nitrogen source needed by Ea273. The ability of 12 strains of Erw. herbicola to produce antibiotics inhibitory to Ea273 on a glucose-asparagine medium correlated with the effectiveness of the strains in suppressing fire blight. A crude preparation of the Eh318 antibiotic delayed development of disease in immature pear fruits incited by Ea273 but not by strain Ea273R318, which is resistant in vitro to the Eh318 antibiotic. Cells of Eh318 protected immature pear fruits more effectively from infection by Ea273 than from the resistant strain Ea273R318.     

Sexual selection against deleterious mutations via variable male search success

In many species, successful mating requires the initial step of actively searching for and locating a female. The overall health or condition of a male is likely to affect their ability to do this, making search effort a potentially important component of sexual fitness that may have important consequences for population mean fitness. We investigated the potential population genetic consequences of search effort using 10 populations of Drosophila melanogaster, each fixed for a different recessive mutation with a visible phenotypic effect. Mate choice trials were conducted in arenas of varying size, requiring different levels of search ability. Sexual selection against mutant males was stronger when increased search effort was included than when it was excluded. Varying abilities to find mates can substantially increase the strength of selection against deleterious alleles.     

Preliminary studies on the effect of moderate physical activity on blood levels of glutathione

Molecular epidemiological approaches are being used to study how physical activity may protect against cancer. Prior epidemiological data suggest that physical activity protects against lung cancer; however, interpretation of these data is complicated by potential confounding by smoking. Glutathione (GSH) detoxifies cigarette smoke carcinogens and the paper tests whether physical activity levels are associated with blood GSH levels. Study subjects were enrolled in a chemoprevention trial testing whether antioxidant micronutrient supplementation reduces genetic damage from cigarette smoking. Physical activity data were collected by questionnaire from 178 subjects at 12 months of follow-up in the trial. Total GSH (tGSH), which is the sum of free and protein-bound GSH and glutathione disulfide levels, was measured using the 5,5'-dithiobis-(2-nitrobenzenoic acid) colormetric assay with red blood cell samples collected at the 12-month time point. In multivariate linear regression analyses that controlled for gender and cigarettes smoked per day, tGSH was positively associated with hours per week of moderate intensity activity (β=0.005, p=0.02). Hours per week of vigorous intensity activity were unassociated with tGSH and the effect of moderate activity remained after control for vigorous activity. The results are consistent with prior research showing differential effects of moderate and vigorous activity and suggest a mechanism through which physical activity may influence lung cancer risk.     

Screening Global Positioning System Location Data for Errors Using Animal Movement Characteristics

Abstract: Animal locations estimated by Global Positioning System (GPS) inherently contain errors. Screening procedures used to remove large positional errors often trade data accuracy for data loss. We developed a simple screening method that identifies locations arising from unrealistic movement patterns. When applied to a large data set of moose (Alces alces) locations, our method identified virtually all known errors with minimal loss of data. Thus, our method for screening GPS data improves the quality of data sets and increases the value of such data for research and management.     

Diet-shifts by an estuarine goby (Pomatoschistus microps) in the face of variable prey availability

Ontogenetic shifts in diet provide a mechanism for maximising fitness throughout development and are common where predators exhibit large increases in size. In order to maximise their fitness throughout development, benthic feeding fish can show diet-shifts that centre on the transition from meiofaunal to macrofaunal prey. Here we assessed whether such a shift was influenced by natural variation in prey-size availability by comparing the sizes of prey consumed by naturally foraging common gobies (Pomatoschistus microps). We tested explicitly for the presence of an ontogenetic shift by analysing the length of prey consumed and an index for prey importance for gobies of different lengths. We also tested the match between actual diets and those predicted by a foraging model. The goby size at which the diet-shift occurred was consistent among locations that differed in their availability of prey and through temporal changes in densities and types of prey. The mean sizes of ingested prey increased for gobies > 35 mm in length and the relative importance of macrofauna increased at 30 mm. The foraging model predicted that gobies > 30 mm would eat larger prey than would smaller gobies which differed from the observed changes in prey-size at 35 mm. Availability of prey did not appear to influence the lengths at which gobies changed diet but did affect the size of prey taken after the diet-shift. A relatively large abundance of large-bodied chironomids at two sites was reflected in the mean size of prey consumed by gobies > 30 mm at these sites. Our study indicates that intrinsic mechanisms can be more important than fluctuating environments in determining prey-choice and shifts in diet, although for the common goby, variability in prey-size may have implications for prey-choice later in ontogeny.     

Chromogranin A, B and C: immunohistochemical localization in ovine pituitary and the relationship with hormone-containing cells

Chromogranins A, B and C, three distinct groups of proteins found in bovine chromaffin granules, were also found to be present in the pituitary using immunoblotting techniques. Their distribution was therefore studied in the normal ram pituitary using an immunoperoxidase technique applied to semithin serial sections and compared with that of some of the hormones of the anterior pituitary. Chromogranin-immunoreactivity was found in gonadotrophs (all three), thyrotrophs (A with some positive for C) and corticotrophs (a fraction with A and fewer with B and C). The mammotrophs and somatotrophs were negative. Chromogranin C was the only one of the three to be located in the pars nervosa, whilst chromogranin B was rarely found in the pars intermedia. The results suggest that chromogranins A, B and C are not always stored together, some hormone-containing cells do not contain immunohistologically detectable levels of the chromogranins.     

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.