Plankton vertical migrations - Implications for the pelagic ecosystem

Habitat selection is an important behavior of many organisms. The direction and strength of this behavior is often characterized as a result of a trade off between predator avoidance and obtaining resources. A characteristic example of this trade off may be seen in organisms in the pelagic ecosystem in the form of vertical migrations. Diel vertical migration (DVM) is a predator avoidance behavior of many zooplankton species, which is marked by a significant shift in the vertical distribution of the zooplankton where night time is spent in the epilimnion and day time in the hypolimnion While the causes of DVM and its ecophysiological consequences for the zooplankton are well studied, little is known about the consequences of DVM for the pelagic food ecosystem. Vertical migrations are not only restricted to zooplankton but are often exhibited by phytoplankton species, which respond to vertical gradients of light and nutrient availability. Many phytoplankton species cope with light and nutrient gradients by changing their position in the water column through active movement or buoyancy adjustment. The costs and consequences of this phytoplankton behavior are hardly studied. In my thesis, I studied the consequences of zooplankton DVM for the pelagic food web and the consequences of phytoplankton vertical migrations on individual growth and biomass composition through both field and laboratory experiments. I, Upward phosphorus transport by Daphnia DVM: During stagnation periods of the water column, physical upward transport processes are very unlikely and nutrients become scarce in the photic zone of many lakes. DVM of zooplankton could be a mechanism of nutrient repletion in the epilimnion. I experimentally examined the upward transport of phosphorus by Daphnia DVM. Results revealed that Daphnia DVM caused an upward nutrient transport. The amount of phosphorus transported and released by Daphnia in my study was within a biologically meaningful range: five percent of the estimated daily maximum phosphorus uptake of the phytoplankton community in the epilimnion. Therefore, nutrient transport by Daphnia DVM could be a significant mechanism in fuelling primary production in the phosphorus limited epilimnion. II, Daphnia DVM: implications beyond zooplankton: DVM creates a temporal and spatial predator-free niche for the phytoplankton, and theoretical models predict that parts of the phytoplankton community could use this niche. I experimentally investigated the influence of Daphnia DVM on the phytoplankton community of an oligotrophic lake in field mesocosms. My results suggest that Daphnia DVM had significant effects on quantitative and qualitative characteristics of the phytoplankton community. Phytoplankton biomass was higher in “no DVM” treatments. DVM also increased diversity in the phytoplankton community. The analyses showed that the gelatinous green algae Planktosphaeria gelatinosa was the main species influencing phytoplankton dynamics in the experiment, and therefore the effects of Daphnia DVM were highly species specific. III, Initial size structure of natural phytoplankton communities determines the response to Daphnia DVM: Previous studies have shown that the direction and strength of phytoplankton responses to zooplankton DVM most likely depends on the size of the phytoplankton species. To examine the influence of DVM on different sized phytoplankton communities, I manipulated the size distribution of a natural phytoplankton community a priori in field mesocosms. The results reveal that DVM oppositely affected the two different phytoplankton communities. A comparison of “DVM” and “no DVM” treatments showed that nutrient availability and total phytoplankton biovolume was higher in “no DVM” treatments of phytoplankton communities consisting mainly of small algae, whereas it was higher in “DVM” treatments of phytoplankton communities with a wide size spectrum of algae. It seemed that two different mechanisms on how DVM can influence the phytoplankton community were at work. In communities of mainly small algae nutrient recycling was important, seemed to be important, whereas in communities with a wide size spectrum of algae the refuge effect played the dominant role. IV, Carbon sequestration and stoichiometry of motile and non-motile green algae: The ability to move actively should entail costs in terms of increased energy expenditure and the provision of specific cell structures for movement. In a laboratory experiment, I studied whether motile, flagellated and non-motile phytoplankton taxa differ with respect to their energetic costs, phosphorus requirements, and structural carbon requirements. The results show that flagellated taxa had higher respiration rates and higher light requirements for growth than non-motile taxa. Accordingly, both short-term photosynthetic rates and long-term biomass accrual were lower for flagellated than for non-motile taxa. My results point at significant costs of motility, which may explain why flagellated taxa are often outcompeted by non-motile taxa in turbulently mixed environments, where active motility is of little use. The data in this study also suggest that motility alone may not be sufficient to explain the lower C: P ratios of flagellates. In summary, my results show that migrating phytoplankton and zooplankton species can act as a vector transporting energy, organic matter and ecological interaction. The complex consequences for the pelagic ecosystem are thereby determined by the organisms´ activity and characterized by their life history

CNOT and Bell-state analysis in the weak-coupling cavity QED regime

We propose an interface between the spin of a photon and the spin of an electron confined in a quantum dot embedded in a microcavity operating in the weak coupling regime. This interface, based on spin selective photon reflection from the cavity, can be used to construct a CNOT gate, a multi-photon entangler and a photonic Bell-state analyzer. Finally, we analyze experimental feasibility, concluding that the schemes can be implemented with current technology.Comment: 4 pages, 2 figure

Nudging als politisches Instrument - gute Absicht oder staatlicher Übergriff?

Die Verhaltensökonomie und ihre praktischen Implikationen geraten immer stärker in den Fokus auch der deutschen Politik. Individuelle Entscheidungen sollen im Sinne eines „libertären Paternalismus“ „sanft“ beeinflusst werden. Die „Nudges“ bestehen in Standardvorgaben, Selbstbindungen und der Informationsbereitstellung. Deren Anwendung setzt allerdings die Klärung einiger Fragen voraus: Wer darf sich anmaßen, für die Wirtschaftssubjekte „kluge“ Entscheidungen zu treffen? Bei welchen Entscheidungen sind Eingriffe einer anderen Instanz begründbar? Mit welchem Zeithorizont und aufgrund welcher Wohlfahrtsüberlegungen wird eine Entscheidung als „richtig“ definiert? Welcher Rationalitätsbegriff steht hinter dem Konzept

Surgical closure of spinal cerebrospinal fluid leaks improves symptoms in patients with superficial siderosis.

BACKGROUND AND PURPOSE Spinal cerebrospinal fluid (CSF) leaks may cause a myriad of symptoms, most common being orthostatic headache. In addition, ventral spinal CSF leaks are a possible etiology of superficial siderosis (SS), a rare condition characterized by hemosiderin deposits in the central nervous system (CNS). The classical presentation of SS involves ataxia, bilateral hearing loss, and myelopathy. Unfortunately, treatment options are scarce. This study was undertaken to evaluate whether microsurgical closure of CSF leaks can prevent further clinical deterioration or improve symptoms of SS. METHODS This cohort study was conducted using data from a prospectively maintained database in two large spontaneous intracranial hypotension (SIH) referral centers in Germany and Switzerland of patients who meet the modified International Classification of Headache Disorders, 3rd edition criteria for SIH. Patients with spinal CSF leaks were screened for the presence of idiopathic infratentorial symmetric SS of the CNS. RESULTS Twelve patients were included. The median latency between the onset of orthostatic headaches and symptoms attributed to SS was 9.5 years. After surgical closure of the underlying spinal CSF leak, symptoms attributed to SS improved in seven patients and remained stable in three. Patients who presented within 1 year after the onset of SS symptoms improved, but those who presented in 8-12 years did not improve. We could show a significant association between patients with spinal longitudinal extrathecal collections and SS. CONCLUSIONS Long-standing untreated ventral spinal CSF leaks can lead to SS of the CNS, and microsurgical sealing of spinal CSF leaks might stop progression and improve symptoms in patients with SS in a time-dependent manner

The shared frameshift mutation landscape of microsatellite-unstable cancers suggests immunoediting during tumor evolution

The immune system can recognize and attack cancer cells, especially those with a high load of mutation-induced neoantigens. Such neoantigens are abundant in DNA mismatch repair (MMR)-deficient, microsatellite-unstable (MSI) cancers. MMR deficiency leads to insertion/deletion (indel) mutations at coding microsatellites (cMS) and to neoantigen-inducing translational frameshifts. Here, we develop a tool to quantify frameshift mutations in MSI colorectal and endometrial cancer. Our results show that frameshift mutation frequency is negatively correlated to the predicted immunogenicity of the resulting peptides, suggesting counterselection of cell clones with highly immunogenic frameshift peptides. This correlation is absent in tumors with Beta-2-microglobulin mutations, and HLA-A*02:01 status is related to cMS mutation patterns. Importantly, certain outlier mutations are common in MSI cancers despite being related to frameshift peptides with functionally confirmed immunogenicity, suggesting a possible driver role during MSI tumor evolution. Neoantigens resulting from shared mutations represent promising vaccine candidates for prevention of MSI cancers. DNA mismatch repair (MMR)-deficient cancers with microsatellite-instability are characterized by a high load of frameshift mutation-derived neoantigens. Here, by mapping the frameshift mutation landscape and predicting the immunogenicity of the resulting peptides, the authors show evidence of immunoediting in MMR-deficient colorectal and endometrial cancers.Peer reviewe

Search for the standard model Higgs boson in the H to ZZ to 2l 2nu channel in pp collisions at sqrt(s) = 7 TeV

A search for the standard model Higgs boson in the H to ZZ to 2l 2nu decay channel, where l = e or mu, in pp collisions at a center-of-mass energy of 7 TeV is presented. The data were collected at the LHC, with the CMS detector, and correspond to an integrated luminosity of 4.6 inverse femtobarns. No significant excess is observed above the background expectation, and upper limits are set on the Higgs boson production cross section. The presence of the standard model Higgs boson with a mass in the 270-440 GeV range is excluded at 95% confidence level.Comment: Submitted to JHE

Search for the standard model Higgs boson decaying into two photons in pp collisions at sqrt(s)=7 TeV

A search for a Higgs boson decaying into two photons is described. The analysis is performed using a dataset recorded by the CMS experiment at the LHC from pp collisions at a centre-of-mass energy of 7 TeV, which corresponds to an integrated luminosity of 4.8 inverse femtobarns. Limits are set on the cross section of the standard model Higgs boson decaying to two photons. The expected exclusion limit at 95% confidence level is between 1.4 and 2.4 times the standard model cross section in the mass range between 110 and 150 GeV. The analysis of the data excludes, at 95% confidence level, the standard model Higgs boson decaying into two photons in the mass range 128 to 132 GeV. The largest excess of events above the expected standard model background is observed for a Higgs boson mass hypothesis of 124 GeV with a local significance of 3.1 sigma. The global significance of observing an excess with a local significance greater than 3.1 sigma anywhere in the search range 110-150 GeV is estimated to be 1.8 sigma. More data are required to ascertain the origin of this excess.Comment: Submitted to Physics Letters