Refine
Year of publication
- 2003 (124) (remove)
Document Type
- Article (97)
- Doctoral Thesis (22)
- Postprint (3)
- Monograph/Edited Volume (1)
- Habilitation Thesis (1)
Keywords
- Biogenic amine (2)
- G protein-coupled receptor (2)
- AT1 receptor / preeclampsia / AT1-AAB / neonatal rat cardiomyocytes / autoantibody / angiotensin II (1)
- AT1-Rezeptor / Präeklampsie / AT1-AAK / neonatale Rattenkardiomyozyten / Autoantikörper / Angiotensin II (1)
- Aktivitätsmessung (1)
- Baculovirus (1)
- Biohybride Organe (1)
- Biomaterialien (1)
- Buchfink (1)
- Ca2+ (1)
- Chaffinch (1)
- Chlamydomonas (1)
- DOC (1)
- Elektronenmikroskopie (1)
- G-quartettes (1)
- Gentherapie (1)
- Gesangsaktivität (1)
- Gesangsangleich (1)
- Gesangsdialekte (1)
- Gesangslernen (1)
- Glanzstreifen (1)
- IC (1)
- Immunoassay; GDH-biosensor; Phenolische Substanzen; Vor-Ort-Analytik; FIA; ß-Galactosidase; Abwasseranalytik (1)
- Invertebrate (1)
- Ionentransport (1)
- Leukocyte Receptor Complex LRC KIR ILT FCAR Immunglobulin Evolution Immunsystem SNP HRCA (1)
- Leukocyte Receptor Complex LRC KIR ILT FCAR immunoglobulin evolution SNP HRCA (1)
- Mining lakes (1)
- Muskel (1)
- Muskel-Sehnen-Verbindung (1)
- Nukleinsäuren (1)
- Periplaneta (1)
- Polymere (1)
- Protein Adsorption (1)
- Proteinsekretion (1)
- Saure Seen (1)
- Songdialects (1)
- Speichel (1)
- Speicheldrüse (1)
- Strophentypen (1)
- TRAP-assay (1)
- Tagebaurestseen (1)
- Telomerase (1)
- Virosomen (1)
- Wachstumsraten (1)
- Xin (1)
- Zelladhäsion (1)
- acidic lakes (1)
- biohybrid organs (1)
- biomaterials (1)
- cAMP (1)
- cationic liposome (1)
- cell adhesion (1)
- chlamydomonas (1)
- cyclic AMP (1)
- electron microscopy (1)
- fibre optic (1)
- gene therapy (1)
- grating coupler (1)
- growthrates (1)
- immunoassay; GDH-biosensor; phenolic compounds; on-site-analysis; FIA;ß-galactosidase; wastewater analysis (1)
- insect (1)
- intercalated disc (1)
- ion transport (1)
- ionale Zusammensetzung (1)
- ionic composition (1)
- kationische Liposomen (1)
- muscle (1)
- myotendinous junction (1)
- on-chip enzymatic assay (1)
- optische Biosensoren (1)
- pH (1)
- polymers (1)
- protein adsorption (1)
- protein secretion (1)
- saliva (1)
- salivary gland (1)
- second messenger (1)
- singing activity (1)
- song-matching (1)
- song-sharing (1)
- song-types (1)
- songlearning (1)
- virosome (1)
Institute
- Institut für Biochemie und Biologie (124) (remove)
In this thesis, I investigated the factors influencing the growth and vertical distribution of planktonic algae in extremely acidic mining lakes (pH 2-3). In the focal study site, Lake 111 (pH 2.7; Lusatia, Germany), the chrysophyte, Ochromonas sp., dominates in the upper water strata and the chlorophyte, Chlamydomonas sp., in the deeper strata, forming a pronounced deep chlorophyll maximum (DCM). Inorganic carbon (IC) limitation influenced the phototrophic growth of Chlamydomonas sp. in the upper water strata. Conversely, in deeper strata, light limited its phototrophic growth. When compared with published data for algae from neutral lakes, Chlamydomonas sp. from Lake 111 exhibited a lower maximum growth rate, an enhanced compensation point and higher dark respiration rates, suggesting higher metabolic costs due to the extreme physico-chemical conditions. The photosynthetic performance of Chlamydomonas sp. decreased in high-light-adapted cells when IC limited. In addition, the minimal phosphorus (P) cell quota was suggestive of a higher P requirement under IC limitation. Subsequently, it was shown that Chlamydomonas sp. was a mixotroph, able to enhance its growth rate by taking up dissolved organic carbon (DOC) via osmotrophy. Therefore, it could survive in deeper water strata where DOC concentrations were higher and light limited. However, neither IC limitation, P availability nor in situ DOC concentrations (bottom-up control) could fully explain the vertical distribution of Chlamydomonas sp. in Lake 111. Conversely, when a novel approach was adopted, the grazing influence of the phagotrophic phototroph, Ochromonas sp., was found to exert top-down control on its prey (Chlamydomonas sp.) reducing prey abundance in the upper water strata. This, coupled with the fact that Chlamydomonas sp. uses DOC for growth, leads to a pronounced accumulation of Chlamydomonas sp. cells at depth; an apparent DCM. Therefore, grazing appears to be the main factor influencing the vertical distribution of algae observed in Lake 111. The knowledge gained from this thesis provides information essential for predicting the effect of strategies to neutralize the acidic mining lakes on the food-web.
Quenching of the triplet state of tryptophan by cysteine has provided a new tool for measuring the rate of forming a specific intramolecular contact in disordered polypeptides. Here, we use this technique to investigate contact formation in the denatured state of CspTm, a small cold-shock protein from Thermotoga maritima, engineered to contain a single tryptophan residue (W29) and a single cysteine residue at the C terminus (C67). At all concentrations of denaturant, the decay rate of the W29 triplet of the unfolded protein is more than tenfold faster than the rate observed for the native protein (not, vert, similar104 s;1). Experiments on the unfolded protein without the added C- terminal cysteine residue show that this faster rate results entirely from contact quenching by C67. The quenching rate in the unfolded state by C67 increases at concentrations of denaturant that favor folding, indicating a compaction of the unfolded protein as observed previously in single-molecule Foerster resonance energy transfer (FRET) experiments.
In recent years most studies of the benthic microbial food web have either been descriptive or were restricted to the measurement of within sediment process rates. Little is known about benthic-pelagic coupling processes such as recruitment. We, therefore, developed an ex situ core incubation procedure to quantify the potential for microbial recruitment from the benthos to the pelagic in an acidic mining lake, Mining Lake 111 (ML 111; pH 2.6), in eastern Germany. Our data suggest that considerable zooplankton recruitment from the benthos takes place. Heliozoan and rhizopod recruitment in both summer and winter sediment cores was highest when they were incubated at 20°C. Maximum heliozoan recruitment was 23 (± 9 s.e.) individuals cm-2 d-1 (40% initial standing stock daily) in the winter 20°C incubation. Maximum rhizopod recruitment was 6 (± 2 s.e.) individuals cm-2 d-1 in the summer 20°C incubation. Little or no recruitment was apparent for either taxa when winter cores were incubated at 5°C, implying a temperature cue. Conversely, the rotifer, Cephalodella hoodi, exhibited a maximum recruitment of 6 (± 2 s.e.) individuals cm-2 d-1 during the winter 5°C incubation, representing 30% of initial standing stock daily, but little recruitment when incubated at 20°C. Cephalodella may have responded to an increased winter benthic food supply; in situ winter Chl a concentrations in the benthos were 3.4 times higher than those in the summer. The importance of this was reinforced by the poor pelagic food supply available in ML 111. In situ, Heliozoa, rhizopods and Cephalodella were first observed in the epilimnion of ML 111 in spring or early summer, suggesting active or passive recruitment following lateral transport from littoral sediments. Benthic-pelagic coupling via recruitment is potentially important in understanding the pelagic food web in ML 111 and warrants further investigation in this and other aquatic environments.
Mixotrophy in the Antarctic phytoflagellate, Pyramimonas gelidicola (Chlorophyta: Prasinophyta)
(2003)
Grazing by the planktonic, phytoflagellate, Pyramimonas gelidicola McFadden (Chlorophyta: Prasinophyta), and heterotrophic nanoflagellates (HNAN) in meromictic, saline Ace Lake in the Vestfold Hills, Eastern Antarctica, was investigated in the austral summers of 1997 and 1999. Up to 47% of the P. gelidicola population ingested fluorescently labelled prey (FLP). Ingestion rates varied with depth. In January 1997 and November 1999, maximum P. gelidicola ingestion rates of 6.95 and 0.79 FLP;cell-1;h-1, respectively, were measured at the chemocline (6-8 m) where a deep chlorophyll maximum composed of phototrophic nanoflagellates (PNAN DCM), predominantly P. gelidicola, persisted all year. During the summers of 1997 and 1999, the grazing P. gelidicola community removed between 0.4 and approximately 16% of in situ bacterial biomass, equivalent to between 4 and >100% of in situ bacterial production. Due to their higher abundance, the community clearance rates of HNAN in Ace Lake generally exceeded those of P. gelidicola but HNAN removed approximately only 3 to 4% of bacterial biomass, equivalent to between 28 and 32% of bacterial production. P. gelidicola growth rates were highest at the PNAN DCM concomitant with the highest ingestion rates. It is estimated that during the summer P. gelidicola can derive up to 30% of their daily carbon requirements from bacterivory at the PNAN DCM. This study confirms mixotrophy as an important strategy by which planktonic organisms can survive in extreme, polar, lacustrine ecosystems.
Application of metabolomics to plant genotype discrimination using statistics and machine learning
(2003)
South Africa's endemic Knysna seahorse, Hippocampus capensis Boulenger 1900, is a rare example of a marine fish listed as Endangered by the IUCN because of its limited range and habitat vulnerability. It is restricted to four estuaries on the southern coast of South Africa. This study reports on its biology in the Knysna and Swartvlei estuaries, both of which are experiencing heavy coastal development. We found that H. capensis was distributed heterogeneously throughout the Knysna Estuary, with a mean density of 0.0089 m-2 and an estimated total population of 89 000 seahorses (95% confidence interval: 30 000 to 148 000). H. capensis was found most frequently in low density vegetation stands ( 20% cover) and grasping Zostera capensis. Seahorse density was not otherwise correlated with habitat type or depth. The size of the area in which any particular seahorse was resighted did not differ between males and females. Adult sex ratios were skewed in most transects, with more males than females, but were even on a 10 m by 10 m focal study grid. Only three juveniles were sighted during the study. Both sexes were reproductively active but no greeting or courtship behaviours were observed. Males on the focal study grid were longer than females, and had shorter heads and longer tails, but were similar in colouration and skin filamentation. The level of threat to H. capensis and our limited knowledge of its biology mean that further scientific study is urgently needed to assist in developing sound management practices.
The classical (Levins) metapopulation scenario envisions a species persisting in a network of habitat patches through a balance between frequent local (within-patch) extinctions and recolonizations. Although this is the dominant paradigm for species in fragmented habitats, empirical support is limited and it has been argued that very restrictive conditions on migration rates are required: high enough for recolonization to balance extinctions, but low enough that local populations do not fluctuate in synchrony. Through simulation and analysis of a stochastic spatial model, we argue that the likelihood of persistence via the classical scenario is strongly affected by some basic properties of within- patch successional dynamics whose importance has not been emphasized in metapopulation theory: the distribution of successional stage durations, and whether patches are "refractory" versus immediately available for recolonization after an extinction has occurred. These properties are tied to the biological causes of extinction (e.g., demographic accident versus regular successional changes) and patch recovery (e.g., recolonization by a host species versus regeneration of an exhausted resource base). Our results indicate that metapopulation theory needs to incorporate the patch-dynamics perspective of a landscape in a dynamic mosaic of successional states, with particular attention to links between colonization-extinction processes and local succession.
Ecological and evolutionary dynamics can occur on similar timescales. However, theoretical predictions of how rapid evolution can affect ecological dynamics are inconclusive and often depend on untested model assumptions. Here we report that rapid prey evolution in response to oscillating predator density affects predator-prey (rotifer-algal) cycles in laboratory microcosms. Our experiments tested explicit predictions from a model for our system that allows prey evolution. We verified the predicted existence of an evolutionary tradeoff between algal competitive ability and defence against consumption, and examined its effects on cycle dynamics by manipulating the evolutionary potential of the prey population. Single-clone algal cultures (lacking genetic variability) produced short cycle periods and typical quarter-period phase lags between prey and predator densities, whereas multi-clonal (genetically variable) algal cultures produced long cycles with prey and predator densities nearly out of phase, exactly as predicted. These results confirm that prey evolution can substantially alter predator-prey dynamics, and therefore that attempts to understand population oscillations in nature cannot neglect potential effects from ongoing rapid evolution.
A characteristic vertical sequence of phytoplankton populations was observed below the metalimnetic oxycline of a stratified, mesotrophic lake. Ceratium spp., Closterium acutum and Aphanizomenon flos- aquae were present in the epilimnion but had distinct population maxima in the microaerobic chemocline. Below these populations, Cryptomonas phaseolus, Planktothrix clathrata, Pseudanabaena catenata and Limnothrix sp. followed each other in the transition zone between the chemocline and the sulphide-containing hypolimnion. The dominating populations of P. clathrata and P. catenata caused a deep chlorophyll maximum. Phytoplankton structure was determined by the vertical gradients of sulphide and light. Compared with the epilimnion, nutrient availability was not fundamentally better below the oxycline but the algae might have benefited from reduced grazing pressure in their habitat.
1. This is a discussion of the applicability to the phytoplankton of the concepts of 'Plant Functional Types' (PFTs) and 'Functional Diversity' (FD), which originated in terrestrial plant ecology. 2. Functional traits driving the performance of phytoplankton species reflect important processes such as growth, sedimentation, grazing losses and nutrient acquisition. 3. This paper presents an objective, mathematical way of assigning PFTs and measuring FD. Ecologists can use this new approach to investigate general hypotheses (e.g. the intermediate disturbance hypothesis (IDH), the insurance hypothesis and synchronicity phenomena), since, for example, in its original formulation the IDH makes its predictions based on FD rather than species diversity.
Recently, much ecological research has focused on predicting invasions of alien species in order to prevent potentially negative effects of such invasions. In this study, we utilize novel methods of landscape ecology for testing the hypothesis that increasing structural diversity correlates with an increasing number of alien plant species. Our overall findings support this hypothesis and suggest that in the studied area (RB Dessau, Sachsen Anhalt, Germany), species richness of neophytes is positively correlated with the diversity in land-use types and structures. However, this relationship between structural diversity and species diversity applied for native spe-cies, too. Furthermore, our results support findings of previous studies which show that neophytes occur mainly in artificially or naturally disturbed areas. Our overall findings highlight the use of landscape-scale ecological methods for studying plant distribution patterns.
Gaps are often important microhabitats for recruitment of herbaceous plants. In the Florida scrub, fires create gaps by top-killing resprouting shrubs. These natural gaps are aboveground gaps (without aboveground vegetation) that may also be complete gaps (if belowground roots and rhizomes are absent). Within three types of gaps (natural gaps, experimental aboveground and experimental complete gaps), we studied seedling recruitment and survival of spontaneous species and seven sown herbs for two years. We created aboveground gaps by clipping vegetation and complete gaps by removing shrub roots and rhizomes. These gaps occurred in two Florida scrub habitats: rosemary scrub and scrubby flatwoods. We also explored factors that can affect recruitment patterns in gaps, such as soil moisture, root water retention and light availability. In addition, we tested effects of supplemental watering on sown seeds in the field since drought in 2000 and 2001 suppressed natural seedling recruitment. The watering treatment increased recruitment in all types of gaps. Over half of all gaps were colonized, but there were few seedlings. Recruitment was highest in watered, complete gaps in scrubby flatwoods, where the soil moisture levels were higher and light levels lower than in the other gap types. Seedlings of a single spontaneously recruited species (Lechea deckertii) were more abundant than sown species. Locally common gap specialists were more abundant than generalists. Because many of these gap specialists are endangered plant species, understanding how disturbances create microsites for their regeneration is critical for conservation and management of the Florida scrub ecosystem. In small-scale conservation projects, artificially created gaps may substitute for post-fire gaps when prescribed burning is impossible.