Interbank Competition with Costly Screening

We analyse credit market equilibrium when banks screen loan applicants. When banks have a convex cost function of screening, a pure strategy equilibrium exists where banks optimally set interest rates at the same level as their competitors. This result complements Broecker s (1990) analysis, where he demonstrates that no pure strategy equilibrium exists when banks have zero screening costs. In our set up we show that interest rate on loans are largely independent of marginal costs, a feature consistent with the extant empirical evidence. In equilibrium, banks make positive profits in our model in spite of the threat of entry by inactive banks. Moreover, an increase in the number of active banks increases credit risk and so does not improve credit market effciency: this point has important regulatory implications. Finally, we extend our analysis to the case where banks have differing screening abilities.

Financial Markets and Real Ecinomy: Four Essays in International Trade

Financial markets play an important role in an economy performing various functions like mobilizing and pooling savings, producing information about investment opportunities, screening and monitoring investments, implementation of corporate governance, diversification and management of risk. These functions influence saving rates, investment decisions, technological innovation and, therefore, have important implications for welfare. In my PhD dissertation I examine the interplay of financial and product markets by looking at different channels through which financial markets may influence an economy.My dissertation consists of four chapters. The first chapter is a co-authored work with Martin Strieborny, a PhD student from the University of Lausanne. The second chapter is a co-authored work with Melise Jaud, a PhD student from the Paris School of Economics. The third chapter is co-authored with both Melise Jaud and Martin Strieborny. The last chapter of my PhD dissertation is a single author paper.Chapter 1 of my PhD thesis analyzes the effect of financial development on growth of contract intensive industries. These industries intensively use intermediate inputs that neither can be sold on organized exchange, nor are reference-priced (Levchenko, 2007; Nunn, 2007). A typical example of a contract intensive industry would be an industry where an upstream supplier has to make investments in order to customize a product for needs of a downstream buyer. After the investment is made and the product is adjusted, the buyer may refuse to meet a commitment and trigger ex post renegotiation. Since the product is customized to the buyer's needs, the supplier cannot sell the product to a different buyer at the original price. This is referred in the literature as the holdup problem. As a consequence, the individually rational suppliers will underinvest into relationship-specific assets, hurting the downstream firms with negative consequences for aggregate growth. The standard way to mitigate the hold up problem is to write a binding contract and to rely on the legal enforcement by the state. However, even the most effective contract enforcement might fail to protect the supplier in tough times when the buyer lacks a reliable source of external financing. This suggests the potential role of financial intermediaries, banks in particular, in mitigating the incomplete contract problem. First, financial products like letters of credit and letters of guarantee can substantially decrease a risk and transaction costs of parties. Second, a bank loan can serve as a signal about a buyer's true financial situation, an upstream firm will be more willing undertake relationship-specific investment knowing that the business partner is creditworthy and will abstain from myopic behavior (Fama, 1985; von Thadden, 1995). Therefore, a well-developed financial (especially banking) system should disproportionately benefit contract intensive industries.The empirical test confirms this hypothesis. Indeed, contract intensive industries seem to grow faster in countries with a well developed financial system. Furthermore, this effect comes from a more developed banking sector rather than from a deeper stock market. These results are reaffirmed examining the effect of US bank deregulation on the growth of contract intensive industries in different states. Beyond an overall pro-growth effect, the bank deregulation seems to disproportionately benefit the industries requiring relationship-specific investments from their suppliers.Chapter 2 of my PhD focuses on the role of the financial sector in promoting exports of developing countries. In particular, it investigates how credit constraints affect the ability of firms operating in agri-food sectors of developing countries to keep exporting to foreign markets.Trade in high-value agri-food products from developing countries has expanded enormously over the last two decades offering opportunities for development. However, trade in agri-food is governed by a growing array of standards. Sanitary and Phytosanitary standards (SPS) and technical regulations impose additional sunk, fixed and operating costs along the firms' export life. Such costs may be detrimental to firms' survival, "pricing out" producers that cannot comply. The existence of these costs suggests a potential role of credit constraints in shaping the duration of trade relationships on foreign markets. A well-developed financial system provides the funds to exporters necessary to adjust production processes in order to meet quality and quantity requirements in foreign markets and to maintain long-standing trade relationships. The products with higher needs for financing should benefit the most from a well functioning financial system. This differential effect calls for a difference-in-difference approach initially proposed by Rajan and Zingales (1998). As a proxy for demand for financing of agri-food products, the sanitary risk index developed by Jaud et al. (2009) is used. The empirical literature on standards and norms show high costs of compliance, both variable and fixed, for high-value food products (Garcia-Martinez and Poole, 2004; Maskus et al., 2005). The sanitary risk index reflects the propensity of products to fail health and safety controls on the European Union (EU) market. Given the high costs of compliance, the sanitary risk index captures the demand for external financing to comply with such regulations.The prediction is empirically tested examining the export survival of different agri-food products from firms operating in Ghana, Mali, Malawi, Senegal and Tanzania. The results suggest that agri-food products that require more financing to keep up with food safety regulation of the destination market, indeed sustain longer in foreign market, when they are exported from countries with better developed financial markets.Chapter 3 analyzes the link between financial markets and efficiency of resource allocation in an economy. Producing and exporting products inconsistent with a country's factor endowments constitutes a serious misallocation of funds, which undermines competitiveness of the economy and inhibits its long term growth. In this chapter, inefficient exporting patterns are analyzed through the lens of the agency theories from the corporate finance literature. Managers may pursue projects with negative net present values because their perquisites or even their job might depend on them. Exporting activities are particularly prone to this problem. Business related to foreign markets involves both high levels of additional spending and strong incentives for managers to overinvest. Rational managers might have incentives to push for exports that use country's scarce factors which is suboptimal from a social point of view. Export subsidies might further skew the incentives towards inefficient exporting. Management can divert the export subsidies into investments promoting inefficient exporting.Corporate finance literature stresses the disciplining role of outside debt in counteracting the internal pressures to divert such "free cash flow" into unprofitable investments. Managers can lose both their reputation and the control of "their" firm if the unpaid external debt triggers a bankruptcy procedure. The threat of possible failure to satisfy debt service payments pushes the managers toward an efficient use of available resources (Jensen, 1986; Stulz, 1990; Hart and Moore, 1995). The main sources of debt financing in the most countries are banks. The disciplining role of banks might be especially important in the countries suffering from insufficient judicial quality. Banks, in pursuing their rights, rely on comparatively simple legal interventions that can be implemented even by mediocre courts. In addition to their disciplining role, banks can promote efficient exporting patterns in a more direct way by relaxing credit constraints of producers, through screening, identifying and investing in the most profitable investment projects. Therefore, a well-developed domestic financial system, and particular banking system, would help to push a country's exports towards products congruent with its comparative advantage.This prediction is tested looking at the survival of different product categories exported to US market. Products are identified according to the Euclidian distance between their revealed factor intensity and the country's factor endowments. The results suggest that products suffering from a comparative disadvantage (labour-intensive products from capital-abundant countries) survive less on the competitive US market. This pattern is stronger if the exporting country has a well-developed banking system. Thus, a strong banking sector promotes exports consistent with a country comparative advantage.Chapter 4 of my PhD thesis further examines the role of financial markets in fostering efficient resource allocation in an economy. In particular, the allocative efficiency hypothesis is investigated in the context of equity market liberalization.Many empirical studies document a positive and significant effect of financial liberalization on growth (Levchenko et al. 2009; Quinn and Toyoda 2009; Bekaert et al., 2005). However, the decrease in the cost of capital and the associated growth in investment appears rather modest in comparison to the large GDP growth effect (Bekaert and Harvey, 2005; Henry, 2000, 2003). Therefore, financial liberalization may have a positive impact on growth through its effect on the allocation of funds across firms and sectors.Free access to international capital markets allows the largest and most profitable domestic firms to borrow funds in foreign markets (Rajan and Zingales, 2003). As domestic banks loose some of their best clients, they reoptimize their lending practices seeking new clients among small and younger industrial firms. These firms are likely to be more risky than large and established companies. Screening of customers becomes prevalent as the return to screening rises. Banks, ceteris paribus, tend to focus on firms operating in comparative-advantage sectors because they are better risks. Firms in comparative-disadvantage sectors finding it harder to finance their entry into or survival in export markets either exit or refrain from entering export markets. On aggregate, one should therefore expect to see less entry, more exit, and shorter survival on export markets in those sectors after financial liberalization.The paper investigates the effect of financial liberalization on a country's export pattern by comparing the dynamics of entry and exit of different products in a country export portfolio before and after financial liberalization.The results suggest that products that lie far from the country's comparative advantage set tend to disappear relatively faster from the country's export portfolio following the liberalization of financial markets. In other words, financial liberalization tends to rebalance the composition of a country's export portfolio towards the products that intensively use the economy's abundant factors.

China´s Economic Security Police Towards ASEAN From

After the economic reforms of 1978, China started rising very fast and started engaging other countries in the region which has served to increase its confidence in the region. In the post cold war period, China was seen as a big threat for the region because of its claims on the South China Sea. Nevertheless, this image was eliminated when China engaged ASEAN and other multilateral and regional organizations. This paper is studying China’s economic and security policies towards ASEAN. Globalization Theory is the theory being used to explain the nature of China-ASEAN relations. This research paper argues that China’s rise is promoting peace in the region. With the engagement policy, China started promoting trade and security co operations based on mutual benefits and dialogues for the peaceful resolutions of the disputes in the region. This contributed greatly to improve China’s image in the region. Additionally, China’s posture during the economic crises of 1997 also greatly contributed to improve its image. Thus, the rise of China is providing opportunity to the other countries in East Asia. Chapter One: Background On China-ASEAN Relations The use of Soft Power and engagement policy by the Chinese government has helped to change China’s image in the region. By using these policies China has been able to clear the feeling of suspicion and mistrust among the Asian states. China has increased its participation in multilateral and regional organizations, such as ASEAN. Due to this China has been able to promote economic and security co-operation among countries in the region. Thus, from being a potential threat China became a potential co-operative partner. Chapter Two: A Look into ASEAN ASEAN was originally formed on 8th August 1967 in Bangkok, Thailand, by Indonesia, Malaysia, the Philippines, Singapore and Thailand. Nevertheless, ASEAN was not the first regional group created to act as forum for dialogue between the leaders of different countries. Thought, it is the only one which could work in the region. The aim of the foundation of ASEAN was to promote peace and stability in the Abstract 2 region and also contain the spread of communism in Southeast Asia. For this reason, China did not engage ASEAN until 1990. However, in 1978 with the establishment of the open up policy China started engaging other countries. It started building trust among its neighboring countries by using soft power. By 1992, China formalized its diplomatic ties with ASEAN as a group. The diplomatic ties between China and ASEAN focus on multilateralism and co-operation as the best way for a more peaceful Asia and the search for common security. Thus, security in the region is promoted through economic co-operation among the states. Therefore the relation between China – ASEAN emphasizes the five principles of peaceful coexistence, mutual benefits in economic co-operation, dialogue promoting trust and the peaceful settlement of disputes. Chapter Three: China-ASEAN Economic Relations Since 1978 The economic reform of 1978 has greatly contributed to the economic development of China. After the adoption of the open up policy, China has been able to establish economic and trade relations with the outside world. The realist school of thought had predicted that Asia will not be stable in the post cold war period. Nevertheless, this has not been the case in Asia. China is growing peacefully with the co-operation of countries in the region. China is establishing strong ties with its neighboring countries. China and ASEAN relations focus on mutual benefit instead of being a zero sum game. Thus these relations are aimed at encouraging trust and economic co-operation in the region. China and ASEAN have agreed on Free Trade to assure that the two parties benefit from the co-operation. The ACFTA will have a great impact on economic, political and security issues. This will enable China to increase its influence in Asia and counterbalance the influences that Japan and U.S have in the region. Chapter Four: China ASEAN Relations in the Security Perspective This Chapter is about China and ASEAN relations on security issue. The new security issues of the post cold war period need to be solved in multilateral way. China as a major power in the region, through its engagement policy has solved most Abstract 3 of the disputes in the region using multilateral means. China has also found ways to solve the dispute over Spratly Islands peacefully, through dialogue using ASEAN. Additionally, China signed the Treaty of Amity in 2003, promoted security initiatives through ARF, Declaration on Conduct of Parties in the South China Sea and documents covering non-traditional security threats, economic co-operation and agricultural co-operation in November 2002, and the Joint Declaration on Strategic. Chapter Five: Finding and Analysis This chapter provides a quantitative and qualitative analysis of the date collected throughout this research. It provides an analysis of how the rise of China is promoting peace in the region. China has been promoting mutual beneficial trade and security co-operation which has increased its influence in the region. China has also been able to solve most of the territorial and border dispute in the region through ASEAN. Thus, ASEAN has amended China’s relations with other countries in the region. Therefore, China’s foreign policy in the region has a big impact in shaping the dynamic relations in East Asia. Conclusion and Recommendations This paper concluded that the relationships between China and ASEAN are contributing to peace in the region. After China engaged ASEAN, it has been able to promote multilateral trade based on mutual benefit. This is clearly emphasized by the CAFTA. Additionally, China has solved most of the dispute in the region. It has also found way for a peaceful resolution of the dispute over Spratly Island. Nowadays, the ASEAN countries don’t see China as a threat to the region. Nevertheless, they’ve adopted deterrence measures such as establishing diplomatic relations with other big powers in the region to assure that the region continues to grow peacefully. Concerning this deterrence measures, I recommend as another way for a continued peaceful growth, the resolution of the outstanding dispute.

Stakeholder Activism, Managerial Entrenchment, and the Congruence of Interests between Shareholders and Stakeholders

We argue that when stakeholder protection is left to the voluntary initiative of managers, concessions to social activists and pressure groups can turn into a self-entrenchment strategy for incumbent CEOs. Stakeholders other than shareholders thus benefit from corporate governance rules putting managers under a tough replacement threat. We show that a minimal amount of formal stakeholder protection, or the introduction of explicit covenants protecting stakeholder rights in the firm charter, may deprive CEOs of the alliance with powerful social activists, thus increasing managerial turnover and shareholder value. These results rationalize a recent trend whereby well-known social activists like Friends of the Earth and active shareholders like CalPERS are showing a growing support for each other s agendas.

A Comparison of the Management Models of Protected Areas between China and the Southern African Region

A Comparison of the Management Models of Protected Areas between China and the African South Region allows reading and evaluating the similarities and differences in the use of management model as a management tool for protected areas in China and South African Region. Specifically, some positive and negative features of the management approaches for the two regions. Secondary data was collected from various related literature such as policy documents, students‟ dissertations/thesis, scientific articles and magazines. Based on the method above, the study found out that China's first nature reserve was the Dingus Mountain Nature Reserve in Zhaoqing, Guangdong province established in 1956. By the end of 2005, about 2,349 nature reserves of various kinds were set up throughout the country, covering a total area of 149.95 million ha and accounting for 15 percent of the total land territory. The study further found that Southern Africa has approximately 4,390 protected areas out of 11487920 total land areas and Eastern Africa has approximately 1838144 protected areas, which is equivalent to 15.0% of the total land areas. South Africa in this region had its first declared natural park in 1926 after Paul Kruger (a war hero) had alerted the authorities of the extinguishing threat of some animal species of region.

The effects of tourism, beachfront development and increased light pollution on nesting Loggerhead turtles Caretta caretta (Linnaeus, 1758) on Sal, Cape Verde Islands

Loggerhead Caretta caretta is now the only species of marine turtle nesting on the island of Sal, Cape Verde Islands. Since 2008, ADTMA - SOS Tartarugas has patrolled all the southern beaches of the island in order to protect nesting females and to collect nesting data. Although hunting is still a major issue, with 90 turtles killed in 2009, habitat loss and light pollution are becoming an ever more serious threat. Construction sites, hotels, apartment buildings and restaurants close to beaches, bright lights and illegal removal of sand are contributing to a marked decrease in the total number of nesting turtles on some beaches. In 2009, beaches on Sal experienced an average increase in nests of 200%, while the beach most affected by construction (Tortuga Beach) saw a decrease of nests of 7.3% (from 19.1% of total number of nests in 2008 to 11.8% in 2010). This beach also recorded a much lower nest to emergence ratio than normal (17.6% of emergences resulting in nests compared to 29.9% in other areas), indicating reluctance to nest due to light pollution and other disturbances.

LSTA Five Year Plan 2003-2007, 2007

The Iowa Commission of Libraries, the State Library’s governing board, convened the Library Services Task Force in August 2000. This group consisted of 46 Iowans from across the state, including librarians from all types of libraries, library trustees, legislators, members of Iowa Regional Library system (now called Library Service Areas) and Area Education Agencies, and citizens. Their mission was to make recommendations to the Commission on positioning libraries to effectively and efficiently meet the future needs of Iowans. Needs and expectations of Iowa Library customers and funding authorities were identified and examined by the Task Force, and are reflected in its recommendations. The Commission received the Task Force recommendations in December 2000, carefully studied them, solicited input from the Iowa library community, and with a few changes, forwarded the recommendations to the Governor and the Iowa General Assembly. These recommendations are now known as Iowa Commission of Libraries priorities and serve as a blueprint for future development of the Iowa library system. A second need assessment was conducted in 2001 as part of the process to formulate the joint Library Service Area – State Library Plan of Service 2003-2005. Biennial development of this plan is mandated by the Code of Iowa. In 2001, Library Service Area and Library Development staff from the State Library chose to completely revamp this plan, and used the process outlined in the The New Planning for Results by Sandra Nelson (the Public Library Association planning model) to do so. The group conducted a strengths/weaknesses/opportunities/threat analysis of the Iowa library situation, identified needs and put them in priority order, and identified service responses. Needs identified by the Library Services Task Force were similar to those identified by the Library Service Area and Library Development staff group. These needs were further analyzed and documented by State Library staff during the development of the LSTA plan. Sources consulted are identified in the text of the LSTA plan and/or listed at the close of this document. The text of the Library Services Task Force report and the documents created during the development of the Plan of Service 2003-2005 are cited in the appendix to this document.

Economic Aspects of Agricultural and Food Biosecurity in the United States, March 2007

Concerns about biosecurity in the food system raise a variety of issues about how the system is presently organized, why it might be vulnerable, what one could reasonably do to better secure it, and the costs of doing so. After presenting some facts about US agriculture and food, this paper considers three economic aspects of the general problem. One is the global problem, or the way biosecurity measures can affect how countries relate to each other and the global consequences that result. Another is how to best manage the immediate aftermath of a realized threat in order to minimize damage. The third is how to seek to prevent realization of the threat. Some policy alternatives are also presented.

Immunology taught by lung dendritic cells.

Dendritic cells (DCs) are leukocytes specialised in the uptake, processing, and presentation of antigen and fundamental in regulating both innate and adaptive immune functions. They are mainly localised at the interface between body surfaces and the environment, continuously scrutinising incoming antigen for the potential threat it may represent to the organism. In the respiratory tract, DCs constitute a tightly enmeshed network, with the most prominent populations localised in the epithelium of the conducting airways and lung parenchyma. Their unique localisation enables them to continuously assess inhaled antigen, either inducing tolerance to inoffensive substances, or initiating immunity against a potentially harmful pathogen. This immunological homeostasis requires stringent control mechanisms to protect the vital and fragile gaseous exchange barrier from unrestrained and damaging inflammation, or an exaggerated immune response to an innocuous allergen, such as in allergic asthma. During DC activation, there is upregulation of co-stimulatory molecules and maturation markers, enabling DC to activate naïve T cells. This activation is accompanied by chemokine and cytokine release that not only serves to amplify innate immune response, but also determines the type of effector T cell population generated. An increasing body of recent literature provides evidence that different DC subpopulations, such as myeloid DC (mDC) and plasmacytoid DC (pDC) in the lungs occupy a key position at the crossroads between tolerance and immunity. This review aims to provide the clinician and researcher with a summary of the latest insights into DC-mediated pulmonary immune regulation and its relevance for developing novel therapeutic strategies for various disease conditions such as infection, asthma, COPD, and fibrotic lung disease.

Cooperative games in strategic form

In this paper we view bargaining and cooperation as an interaction superimposed on a strategic form game. A multistage bargaining procedure for N players, the proposer commitment procedure, is presented. It is inspired by Nash s two-player variable-threat model; a key feature is the commitment to threats. We establish links to classical cooperative game theory solutions, such as the Shapley value in the transferable utility case. However, we show that even in standard pure exchange economies the traditional coalitional function may not be adequate when utilities are not transferable.

Determination of oseltamivir and oseltamivir carboxylate in human plasma by liquid chromatography-tandem mass spectrometry

Introduction: Oseltamivir phosphate (OP), the prodrug of oseltamivir carboxylate (OC; active metabolite), is marketed since 10 years for the treatment of seasonal influenza flu. It has recently received renewed attention because of the threat of avian flu H5N1 in 2006-7 and the 2009-10 A/H1N1 pandemic. However, relatively few studies have been published on OP and OC clinical pharmacokinetics. The disposition of OC and the dosage adaptation of OP in specific populations, such as young children or patients undergoing extrarenal epuration, have also received poor attention. An analytical method was thus developed to assess OP and OC plasma concentrations in patients receiving OP and presenting with comorbidities or requiring intensive care. Methods: A high performance liquid chromatography coupled to tandem mass spectrometry method (HPLC-MS/MS) requiring 100-µL aliquot of plasma for quantification within 6 min of OP and OC was developed. A combination of protein precipitation with acetonitrile, followed by dilution of supernant in suitable buffered solvent was used as an extraction procedure. After reverse phase chromatographic separation, quantification was performed by electro-spray ionization-triple quadrupole mass spectrometry. Deuterated isotopic compounds of OP and OC were used as internal standards. Results: The method is sensitive (lower limit of quantification: 5 ng/mL for OP and OC), accurate (intra-/inter-assay bias for OP and OC: 8.5%/5.5% and 3.7/0.7%, respectively) and precise (intra-/inter-assay CV%: 5.2%/6.5% and 6.3%/9.2%, respectively) over the clinically relevant concentration range (upper limits of quantification 5000 ng/mL). Of importance, OP, as in other previous reports, was found not to be stable ex vivo in plasma on standard anticoagulants (i.e. EDTA, heparin or citrate). This poor stability of OP has been prevented by collecting blood samples on commercial fluoride/oxalate tubes. Conclusions: This new simple, rapid and robust HPLC-MS/MS assay for quantification of OP and OC plasma concentrations offers an efficient tool for concentration monitoring of OC. Its exposure can probably be controlled with sufficient accuracy by thorough dosage adjustment according to patient characteristics (e.g. renal clearance). The usefulness of systematic therapeutic drug monitoring in patients appears therefore questionable. However, pharmacokinetic studies are still needed to extend knowledge to particular subgroups of patients or dosage regimens.

Neuroticism modifies psychophysiological responses to fearful films

Background: Neuroticism is a personality component frequently found in anxious and depressive psychiatric disorders. The influence of neuroticism on negative emotions could be due to its action on stimuli related to fear and sadness, but this remains debated. Our goal was thus to better understand the impact of neuroticism through verbal and physiological assessment in response to stimuli inducing fear and sadness as compared to another negative emotion (disgust).¦Methods: Fifteen low neurotic and 18 high neurotic subjects were assessed on an emotional attending task by using film excerpts inducing fear, disgust, and sadness. We recorded skin conductance response (SCR) and corrugator muscle activity (frowning) as indices of emotional expression.¦Results: SCR was larger in high neurotic subjects than in low neurotics for fear relative to sadness and disgust. Moreover, corrugator activity and SCR were larger in high than in low neurotic subjects when fear was induced.¦Conclusion: After decades of evidence that individuals higher in neuroticism experience more intense emotional reactions to even minor stressors, our results indicate that they show greater SCR and expressive reactivity specifically to stimuli evoking fear rather than to those inducing sadness or disgust. Fear processing seems mainly under the influence of neuroticism. This modulation of autonomic activity by neurotics in response to threat/fear may explain their increased vulnerability to anxious psychopathologies such as PTSD (post traumatic stress disorder).

Let's (not) talk about sex: The effect of information provision on gender differences in performance under competition

We study how gender differences in performance under competition areaffected by the provision of information regarding rival s gender and/ordifferences in relative ability. In a laboratory experiment, we use two tasks thatdiffer regarding perceptions about which gender outperforms the other. Weobserve women s underperformance only under two conditions: 1) tasks areperceived as favoring men and 2) rivals gender is explicitly mentioned. Thisresult can be explained by stereotype-threat being reinforced when explicitlymentioning gender in tasks in which women already consider they are inferior.Omitting information about gender is a safe alternative to avoid women sunderperformance in competition.

The economics of anti-parasite defences in animal societies

RESUME : De nombreuses espèces animales vivent en groupe. Du simple grégarisme aux colonies hautement intégrées de fourmis, la vie sociale a atteint des degrés divers de complexité. Les nombreuses interactions entre membres d'une société favorisent la transmission de parasites. Cela représente un coût potentiel de la vie sociale. Cette thèse s'intéresse aux défenses permettant de réduire le coût du parasitisme dans les colonies de fourmis ainsi qu'à la manière dont le parasitisme a pu façonner certains aspects de ces sociétés. Les colonies de fourmis des bois (Forimica paralugubris) contiennent de grandes quantités de résine de conifères. Cette résine réduit la densité microbienne dans le nid et augmente la survie des ouvrières lors d'infections parasitaires. Dans cette thèse, nous montrons, d'une part, que les ouvrières collectent activement la résine et que ce comportement est plutôt préventif que curatif et, d'autre part, que la résine permet aux ouvrières une utilisation moindre de leurs défenses immunitaires. Ces résultats permettent de conclure que ce comportement réduit l'exposition au parasitisme et qu'il a une fonction adaptative. L'émergence d'un tel comportement de médication chez une espèce d'insectes sociaux illustre le fait que la socialité, bien yue provoquant une exposition accrue au parasitisme, permet également l'émergence de mécanismes sociaux de défense. II a été suggéré que la présence de plusieurs reines au sein d'un même nid (polygynie) améliore la résistance aux parasites en augmentant la diversité génétique au sein de la colonie. En accord avec cette hypothèse, nous montrons qu'une augmentation de la diversité génétique au sein de groupes expérimentaux de Formica selysi améliore leur survie lors d'une infection parasitaire. Cependant, nous suggérons également que sur le terrain, d'autres facteurs corrélés à la polygynie ont des effets antagoniques sur la résistance. Nous montrons par exemple que les ouvrières polygynes semblent avoir une capacité moindre à monter une réponse immunitaire. Certains aspects de la reproduction des fourmis ont pu également être façonnés par le parasitisme. L'accouplement n'a lieu que lors d'une courte période au début de la vie adulte, généralement à l'extérieur de la colonie. Les reines stockent ensuite le sperme et l'utilisent parcimonieusement au cours de leur vie alors que les males meurent rapidement. Nous montrons que les défenses immunitaires des reines de fourmis des bois (F. paralugubris) sont fortement affectées par l'accouplement. Ces modulations immunitaires sont probablement liées à une augmentation de l'exposition au parasitisme lors de l'accouplement ainsi qu'à des blessures copulatoires. I1 semble donc que l'accouplement soit accompagné de coûts immunitaires pour les reines. Dans son ensemble, cette thèse illustre la diversité des mécanismes de défenses contre les parasites dans les sociétés de fourmis. La vie sociale, en offrant un nouveau niveau d'interaction, permet en effet l'émergence d'adaptations originales. Cela explique probablement le grand succès écologique des espèces sociales. SUMMARY : Sociality is widespread among animals and has reached variable degrees of complexity, from loose social Groups to highly integrated ant colonies. The many interactions between members of a social group promote the spread of parasites, but social life also permits the evolution of original defence mechanisms. This thesis sheds light on how ant colonies defend themselves against parasites, and on how parasitism shapes certain aspects of these societies. Wood ants nests (Formica paralugubris) contain large amounts of conifer resin which reduces the microbial density in ant nests and enhances the survival of ants challenged by some pathogens. We show that resin is actively collected by workers and that resin collection is rather a prophylactic than a curative behaviour. Moreover, we suggest that resin reduces the use of the immune defences of workers. Altogether, these results indicate that the use of resin is a collective adaptation to prevent the spread of parasites. The emergence of medication in a social insect species illustrates that sociality does not only increase the exposure to parasites but also allows the emergence of social mechanisms to counter this threat. The number of reproducing queens per colony is a variable trait in ants. It has been suggested that polygyny (the occurrence of multiple queens within a colony), by increasing the colonial genetic diversity, improves disease resistance. In line with this hypothesis, we show that in a socially polymorphic ant (Formica selysi), an experimental increase of colony genetic diversity enhances disease resistance. However, we also suggest that factors covarying with queen number variation in the field have antagonistic effects on parasite resistance. We show for instance that polygyne workers seem to have lower immune defences. Parasites may also shape some aspects of ant queen reproductive biology. Ant queens mate at the beginning of their adult life, usually outside of the colony, and store sperm for several years to fertilize eggs. Males die shortly after mating and queens never remate later in life, which drastically reduces sexual conflicts. Moreover, mating and nest founding occur away from the collective defence mechanisms of the natal colony and might be associated with an increased risk of parasitism. We show that mating affects the immune defences of wood ant queens (F. paralugubris) in multiple ways that are consistent with mating wounds and increased risk of parasitism. We suggest that mating is associated with immunity costs in ants, despite the reduced level of sexual conflicts. Altogether, my thesis illustrates the diversity of anti-parasite mechanisms in ant societies. This sheds light on how sociality, by offering a new level of interactions, allows the evolution of original adaptations, which may explain the wide ecological success of social species.

Campaign rhetoric: A model of reputation

We analyze conditions under which a candidate's campaignrhetoric may affect the beliefs of the voters over whatpolicy the candidate will implement in case he wins theelection. We develop a model of repeated elections withcomplete information in which candidates are purely ideological. Voter's strategies involve a credible threat to punish candidates that renege of their campaignpromises, and in equilibrium all campaign promises arebelieved by voters, and honored by candidates. We obtainthat the degree to which promises are credible in equilibriumis an increasing function of the value of a candidate'sreputation.