Biomedical subjects

Bernhard Schmid

Publications and source records attributed to Bernhard Schmid.

5 recordsLinked to original sources

PubMed2003

Dietary shift and lowered biomass gain of a generalist herbivore in species-poor experimental plant communities.

Species loss of primary producers is likely to affect processes on other trophic levels. We studied consumption and individual performance of the generalist herbivore Parapleurus alliaceus (Orthoptera) in relation to the species richness of primary producers. Adult grasshoppers were caged and left to feed for 2 weeks on experimental grassland communities ranging in plant species richness from one, two, four, eight to 32 species. Low plant diversity had a negative effect on both plant community biomass and on biomass gain of female grasshoppers, feeding to produce eggs (male grasshoppers did not gain biomass during the feeding period). This was surprising because plots with high plant diversity had a low proportion of grass biomass and grasshoppers preferentially selected grasses, leading to a greater exploitation of grasses in experimental communities of higher diversity. Thus, the concurrent increase in non-grass species in the diet from these high-diversity communities must have been beneficial to the generalist herbivore. In addition to the positive effects of plant diversity, the presence of legumes in a mixture with grasses further enhanced the biomass gain of grasshoppers at a given level of diversity. These findings suggest that plant species loss may lead to shifts in herbivore population sizes, reducing those of generalists and benefiting specialists of the remaining plant species. Our results further suggest that generalist herbivores, by having feeding preferences, can also change the relative abundances of plant species with different functional characteristics. This may feedback on both composition and diversity of plant communities.

Animals↗

PubMed2003

Acylation of lysophosphatidylcholine plays a key role in the response of monocytes to lipopolysaccharide.

Mononuclear phagocytes play a pivotal role in the progression of septic shock by producing tumor necrosis factor-alpha (TNF-alpha) and other inflammatory mediators in response to lipopolysaccharide (LPS) from Gram-negative bacteria. Our previous studies have shown monocyte and macrophage activation correlate with changes in membrane phospholipid composition, mediated by acyltransferases. Interferon-gamma (IFN-gamma), which activates and primes these cells for enhanced inflammatory responses to LPS, was found to selectively activate lysophosphatidylcholine acyltransferase (LPCAT) (P < 0.05) but not lysophosphatidic acid acyltransferase (LPAAT) activity. When used to prime the human monocytic cell line MonoMac 6, the production of TNF-alpha and interleukin-6 (IL-6) was approximately five times greater in cells primed with IFN-gamma than unprimed cells. Two LPCAT inhibitors SK&F 98625 (diethyl 7-(3,4,5-triphenyl-2-oxo2,3-dihydro-imidazole-1-yl)heptane phosphonate) and YM 50201 (3-hydroxyethyl 5,3'-thiophenyl pyridine) strongly inhibited (up to 90%) TNF-alpha and IL-6 production in response to LPS in both unprimed MonoMac-6 cells and in cells primed with IFN-gamma. In similar experiments, these inhibitors also substantially decreased the response of both primed and unprimed peripheral blood mononuclear cells to LPS. Sequence-based amplification methods showed that SK&F 98625 inhibited TNF-alpha production by decreasing TNF-alpha mRNA levels in MonoMac-6 cells. Taken together, the data from these studies suggest that LPCAT is a key enzyme in both the pathways of activation (priming) and the inflammatory response to LPS in monocytes.

1-Acylglycerophosphocholine O-Acyltransferase↗

PubMed2003

Population size and identity influence the reaction norm of the rare, endemic plant Cochlearia bavarica across a gradient of environmental stress.

Habitat degradation and loss can result in population decline and genetic erosion, limiting the ability of organisms to cope with environmental change, whether this is through evolutionary genetic response (requiring genetic variation) or through phenotypic plasticity (i.e., the ability of a given genotype to express a variable phenotype across environments). Here we address the question whether plants from small populations are less plastic or more susceptible to environmental stress than plants from large populations. We collected seed families from small (<100) versus large natural populations (>1,000 flowering plants) of the rare, endemic plant Cochlearia bavarica (Brassicaceae). We exposed the seedlings to a range of environments, created by manipulating water supply and light intensity in a 2 x 2 factorial design in the greenhouse. We monitored plant growth and survival for 300 days. Significant effects of offspring environment on offspring characters demonstrated that there is phenotypic plasticity in the responses to environmental stress in this species. Significant effects of population size group, but mainly of population identity within the population size groups, and of maternal plant identity within populations indicated variation due to genetic (plus potentially maternal) variation for offspring traits. The environment x maternal plant identity interaction was rarely significant, providing little evidence for genetically- (plus potentially maternally-) based variation in plasticity within populations. However, significant environment x population-size-group and environment x population-identity interactions suggested that populations differed in the amount of plasticity, the mean amount being smaller in small populations than in large populations. Whereas on day 210 the differences between small and large populations were largest in the environment in which plants grew biggest (i.e., under benign conditions), on day 270 the difference was largest in stressful environments. These results show that population size and population identity can affect growth and survival differently across environmental stress gradients. Moreover, these effects can themselves be modified by time-dependent variation in the interaction between plants and their environment.

Biological Evolution↗

PubMed2002

Diversity-dependent production can decrease the stability of ecosystem functioning.

There is concern that species loss may adversely affect ecosystem functioning and stability. But although there is evidence that biodiversity loss can lead to reductions in biomass production, there is no direct evidence that biodiversity loss affects ecosystem resistance (ability to withstand perturbation) or resilience (recovery from perturbation). Yet theory, laboratory experiments and indirect experimental evidence strongly suggest that diversity and stability are related. Here we report results from a field experiment with factorially crossed perturbation and diversity manipulations. We simulated drought perturbation on constructed grassland ecosystems containing 1, 2, 4, 8 or 32 plant species. Under unperturbed conditions, the species-poor systems achieved lower biomass production than the species-rich systems. However, the species-poor systems were more resistant to perturbation than the species-rich systems. The species-poor systems also showed a larger initial resilience following perturbation, although the original relationship between diversity and productivity was fully restored after 1year. Our results confirm that biodiversity increases biomass production, but they also point to the fact that such diversity--production associations may lead to an inverse relationship between biodiversity and the stability of ecosystem functioning.

Ecosystem↗

PubMed2002

Experimental life-history evolution: selection on the allocation to sexual reproduction and its plasticity in a clonal plant.

Allocation to sexual reproduction is an important life-history trait in clonal plants. Different selection pressures between competitive and competition-free environments are likely to result in the evolution of specialized genotypes and to maintain genetic variation in reproductive allocation. Moreover, selection may also result in the evolution of plastic allocation strategies. The necessary prerequisite for evolution, heritable genetic variation, can best be studied with selection experiments. Starting from a base population of 102 replicated genotypes of the clonal herb Ranunculus reptans, we imposed selection on the proportion of flowering rosettes in the absence of competition (base population: mean = 0.391, broad-sense heritability = 0.307). We also selected on the plasticity in this trait in response to competition with a naturally coexisting grass in a parallel experiment (base population: 14% lower mean in the presence of competition, broad-sense heritability = 0.072). After two generations of bidirectional selection, the proportion of flowering rosettes was 26% higher in the high line than in the low line (realized heritability +/- SE = 0.205 +/- 0.017). Moreover, genotypes of the high line had 11% fewer carpels per flower, a 22% lower proportion of rooted rosettes, and a 39% smaller average distance between rosettes within a clone. In the second experiment, we found no significant responses to selection for high and low plasticity in the proportion of flowering rosettes (realized heritability +/- SE = -0.002 +/- 0.013). Our study indicates a high heritability and potential for further evolution of the proportion of flowering rosettes in R. reptans, but not for its plasticity, which may have been fixed by past evolution at its current level. Moreover, our results demonstrate strong genetic correlations between allocation to sexual reproduction and other clonal life-history characteristics.

Biological Evolution↗