Biomedical subjects

Vera Thoss

Publications and source records attributed to Vera Thoss.

3 recordsLinked to original sources

PubMed2006

The role of genetic and chemical variation of Pinus sylvestris seedlings in influencing slug herbivory.

This study investigated the genetic and chemical basis of resistance of Pinus sylvestris seedlings to herbivory by a generalist mollusc, Arion ater. Using feeding trials with captive animals, we examined selective herbivory by A. ater of young P. sylvestris seedlings of different genotypes and correlated preferences with seedling monoterpene levels. We also investigated the feeding responses of A. ater to artificial diets laced with two monoterpenes, Delta(3)-carene and alpha-pinene. Logistic regression indicated that two factors were the best predictors of whether seedlings in the trial would be consumed. Individual slug variation (replicates) was the most significant factor in the model; however, alpha-pinene concentration (also representing beta-pinene, Delta(3)-carene and total monoterpenes due to multicollinearity) of needles was also a significant factor. While A. ater did not select seedlings on the basis of family, seedlings not eaten were significantly higher in levels of alpha-pinene compared to seedlings that were consumed. We also demonstrated significant genetic variation in alpha-pinene concentration of seedlings between different families of P. sylvestris. Nitrogen and three morphological seedling characteristics (stem length, needle length and stem diameter) also showed significant genetic variation between P. sylvestris families. Artificial diets laced with high (5 mg g(-1) dry matter) quantities of either Delta(3)-carene or alpha-pinene, were eaten significantly less than control diets with no added monoterpenes, supporting the results of the seedling feeding trial. This study demonstrates that A. ater selectively feed on P. sylvestris seedlings and that this selection is based, in part, on the monoterpene concentration of seedlings. These results, coupled with significant genetic variation in alpha-pinene concentration of seedlings and evidence that slug herbivory is detrimental to P. sylvestris fitness, are discussed as possible evidence for A. ater as a selective force on the evolution of defensive chemistry in P. sylvestris.

Animals↗

PubMed2005

Browse selection in response to simulated seasonal changes in diet quality through postingestive effects.

Browse species undergo seasonal changes in nutritional value and secondary plant compound concentrations. The capacity of herbivores to monitor such change through postingestive effects and to modify their food choice appropriately was investigated. Twenty-four goats were offered a different conifer species on four successive learning days per 7-d period for six periods. During conifer consumption on learning days, animals received either a positive or a negative digestive stimulus to simulate the nutritional rewards and toxic consequences of browse consumption. For each animal, a different postingestive stimulus treatment was associated with each conifer species. The treatments consisted of an increasing positive stimulus, a decreasing positive stimulus, an increasing negative stimulus, or a decreasing negative stimulus. The levels of the stimuli were adjusted in 20% increments in successive periods (from 0 to 100% for the increasing treatments and from 100 to 0% in the decreasing treatments) to simulate seasonal changes in browse characteristics. Diet preference was measured on d 5 of each period. Animals adjusted their diet choice in response to the changing intensity of the negative stimulus, but not the positive stimulus. Animals avoided foods associated with the negative stimulus to a greater extent when the stimulus was increasing each period compared to when it was decreasing. The results suggest that herbivores are adept at monitoring and responding to temporal change in secondary compound concentrations through assessing their changing postingestive effects and adjusting their food choice accordingly.

Animal Feed↗

PubMed2002

Quantifying the phenolic content of freshwaters using simple assays with different underlying reaction mechanisms.

Five different assays, Gibbs, Prussian Blue, Folin-Ciocalteau, fluorescence quenching of added phenol and precipitation of phenolics with bovine serum albumin (BSA) were investigated for their suitability in measuring the phenolic content of freshwaters. Phenol and a hydrolysable tannic acid were used as standards for monophenolics and polyphenolics, respectively. The individual and simultaneous application of both standards in doubly distilled water and filtered freshwater samples showed no matrix interference for the Gibbs, the Prussian Blue and the Folin-Ciocalteau assays. The quenching of phenol fluorescence and incomplete precipitation of added tannic acid in the freshwater samples were thought to originate from complexation. The Gibbs assay was specific for monophenolics, monohydroxybenzenes, with a Criterion of Detection (CoD) of 0.027 mg l(-1). Evaluating the assay using twenty-two monophenolics of lignin origin showed, apart from phenol itself, the phenolic acids vanillic, isovanillic, ferulic and syringic to have a linear response between 0 and 10 microM. The other monophenolics were not responsive in the Gibbs assay. The oxidation-based assays Prussian Blue and Folin-Ciocalteau had a CoD of 0.169 and 0.025 mg l(-1), respectively. The ratio of response of both assays for each sample was taken as an indication of the degree of polymerisation of the phenolic content. The Folin-Ciocalteau assay was used directly on the samples, on samples spiked with tannic acid at 2 and 4 mg l(-1), and after precipitation of phenolics with BSA. The difference in tannic acid equivalents before and after treatment, assayed the amount of protein precipitated phenolics. The results of all assays allowed differentiation between monophenolics (Gibbs), polyphenolics (Prussian Blue), total phenolics (Folin-Ciocalteau), complexation of added phenol and protein-precipitated phenolics. The reaction mechanisms underlying the assays were matched onto those occurring during humification. The assays were applied to six filtered freshwater samples and two humic and two fulvic acids. The results showed a different pattern for each site and illustrated varying reactivity of the 'phenolic content' of freshwater.

Benzopyrans↗