Contributions in Merlin

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Despite the importance of mutualism as a key ecological process, its persistence in nature is difficult to explain since the existence of exploitative, ‘cheating’ partners that could erode the interaction is common. By analogy with the proposed policing strategy stabilizing intraspecific cooperation, host sanctions against non N2 fixing, cheating symbionts have been proposed as a force stabilizing mutualism in legume-Rhizobium symbiosis. Following this proposal, penalizations would include decreased nodular rhizobial viability and/or early nodule senescence in nodules occupied by cheating rhizobia. In this work, we analyze the stability of Rhizobium-legume symbiosis when “cheating” strains are present, using an experimental and modelling approach. We used split-root experiments with soybean plants inoculated with two rhizobial strains, a cooperative, normal N2 fixing strain and an isogenic non-fixing, “perfect” cheating mutant derivative that lacks nitrogenase activity but has the same nodulation abilities inoculated to split-root plants. We found no experimental evidence of functioning plant host sanctions to cheater rhizobia based on nodular rhizobia viability and nodule senescence and maturity molecular markers. Based on these experiments, we developed a population dynamic model with and without the inclusion of plant host sanctions. We show that plant populations persist in spite of the presence of cheating rhizobia without the need of incorporating any sanction against the cheater populations in the model, under the realistic assumption that plants can at least get some amount of fixed N2 from the effectively mutualistic rhizobia occupying some nodules. Inclusion of plant sanctions merely reduces the time needed for reaching plant population equilibrium and leads to the unrealistic effect of ultimate extinction of cheater strains in soil. Our simulation results are in agreement with increasing experimental evidence and theoretical work showing that mutualisms can persist or even improve in presence of cheating partners.

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This thesis investigates the impact of U.S. government backing announcements on credit default swap (CDS) spread changes of U.S., European and Japanese financial institutions during the financial crisis 2008 to 2009. An event study shows that CDS spreads of both U.S. and European financial institutions react significantly to support measures announced by U.S. federal agencies and the FED, although European firms only to a minor extent. These announcements effects are most pronounced for depository institutions and insurance companies. A regression analysis reveals that a certain level of ownership concentration is significantly related to CDS spread changes, whereas firm size has no significant influence.

This work analyzes the role of credit default swaps (CDSs) during the global financial crisis. It discusses their implied contribution to the turmoil and assesses recent regulatory propositions. Furthermore, the usability of CDS for anticipating credit events throughout the crisis is compared with ratings, bonds and stocks. Results show that on average ratings lag behind entity failure events by at least two days. In contrast, all market-based indicators reflect the increased hazard prior to such events. In addition, the research suggests that the stock and CDS markets clearly lead the bond market, while no clear leadership between stocks and CDS was found.

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