The genetics and genomics of Trypanosoma cruzi

Trypanosoma cruzi is a kinetoplastid parasite that causes Chagas disease. Trypanosomes are unusual organisms in many aspects of its genetics and molecular and cellular biology and considered a paradigm of the exception of the rule in the eukaryotic kingdom. The complete genome sequence of T. cruzi was published in 2005, thus, providing a major tool to the understanding of several of his unusual aspects. However, with so many different mechanisms between the parasite and its mammalian host there is still a lack of availability of effective antiparasitic drugs or disease treatments, specially in the chronic phase. This review highlights the fundamentals of the fasci- nating genetics and genomics of T. cruzi with emphasis in the differential mechanisms that could provide interesting therapeutic targets.Fil: Vazquez, Martin Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres"; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentin

Tales of serial exploration

In this paper, we examine the firm and ecological factors that affect the long-term sustainability of exploration. We analysed the investment decisions by US venture capital firms to enter new technological domains over a 43-year period. Our results suggest that in addition to the well studied effects of inertia and slack, exploration is affected by an organization´s knowledge specialization, is conducive to repetitive momentum, and affects an organization´s subsequent exploration when occurring early in an organization´s life. We contribute to the literature on organizational learning by identifying some of the antecedents of exploration and its sustenance over time.

Patrones temporales en la abundancia y uso de residuos por Gaviotas cocineras (Larus dominicanus) en un basural urbano y pesquero de la costa norte de Patagonia, Argentina

We quantified the use by Kelp Gulls (Larus dominicanus) of urban and fishery waste sites at Puerto Madryn, Argentina, during 1996 and 1997. Kelp Gulls were present at all monthly counts made at both waste sites throughout the two years of the study. Total numbers of gulls in each month were high and variable, with a mean of 4724 and 4612 individuals in 1996 and 1997, respectively. The mean number of gulls at the fishery waste site was significantly larger than at the urban waste site (3767 vs 901). Adult Kelp Gulls were significantly more abundant than non-adult gulls at every count at both the urban and fishery waste sites (mean = 811 vs 91 and 3147 vs 628, respectively). Among the younger age classes, individuals in their third year were the least abundant. The proportion of adults with respect to total gulls present was high during all visits to both sites, although it showed a slight decrease in the fishery waste site during the breeding season. During the breeding season, the number of gulls varied significantly throughout the day at both sites while, during the non-breeding season, numbers varied significantly only in the urban waste site. The Puerto Madryn fishery waste site constitutes a more attractive food source than the urban waste site probably due to the higher quality and quantity of discarded food. The use of waste sites at Puerto Madryn may be enhancing gull breeding success and individual survival during the winter, particularly of young birds. Potential conflicts due to Kelp Gull use of waste sites and the effects on their populations could be minimized by adequate urban and fish waste managementCuantificamos el uso por la Gaviota cocinera (Larus dominicanus) de los basurales urbanos y pesqueros en Puerto Madryn, Argentina, durante 1996 y 1997. La Gaviota cocinera estuvo presente en todos los censos mensuales efectuados en ambos basurales durante los dos años. Los números totales de gaviotas en cada mes fueron altos y variables, con una media de 4724 y 4612 individuos en 1996 y 1997, respectivamente. El número medio de gaviotas en el basural pesquero fue significativamente mayor que en el basural urbano (3767 vs 901). En todos los conteos en los basurales pesquero y urbano, las gaviotas adultas fueron significativamente más abundantes que las no adultas (media = 811 vs 91 y 3147 vs 628, respectivamente). Entre las clases de edad más jóvenes, los individuos del tercer año fueron los menos abundantes. La proporción de adultos respecto al total de gaviotas presentes fue alta en todas las visitas a ambos basurales, aunque mostró una leve disminución en el basural pesquero durante la temporada reproductiva. Durante la temporada reproductiva, el número de gaviotas varió significativamente a lo largo del día en ambos basurales, mientras que en la temporada no reproductiva los números variaron significativamente solo en el basural urbano. El basural pesquero de Puerto Madryn constituye una fuente de alimento más atractiva que el basural urbano, probablemente debido a la mayor cantidad y calidad de los residuos depositados. El uso de los basurales en Puerto Madryn podría estar favoreciendo el éxito reproductivo de las gaviotas y la supervivencia individual durante el invierno, particularmente de aves jóvenes. Los conflictos potenciales resultantes del uso por la Gaviota cocinera de los basurales y los efectos sobre sus poblaciones podrían ser minimizados con un adecuado manejo de los residuos urbanos y pesquerosFil: Giaccardi, Micel. Secretaría de Turismo y Áreas Protegidas; ArgentinaFil: Yorio, Pablo Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; Argentina. Wildlife Conservation Society; Estados Unido

Exerting local tax effort or lobbying for central transfers?: Evidence from Argentina

In many countries fiscal decentralization characterizes the relationship among different levels of government. In those countries, local authorities have the prerogative to tax their constituencies. However, fiscal decentralization is seldom balanced in terms of tax and expenditure assignments. In order to equalize tax capacities, to internalize spillovers or to achieve national policy objectives, central governments often provide transfers to lower levels of government. These transfers may affect the incentives to manage or to improve fiscal performance. Specifically, according to Litvack, Ahmad and Bird (1998), such transfers may induce low `tax effort' in the regions. The purpose of this paper is to investigate theoretically and empirically this relationship between intergovernmental transfers and local tax effort. An initial problem to deal with is the definition of `tax effort' in itself. First, one can associate tax effort to high tax rates. Smart (1998) asserted that such association is inadequate. Second, one can measure tax effort using actual tax revenues or the difference between actual the predicted value of tax revenues. This approach has been mainly adopted by the empirical literature on the relationship between intergovernmental transfers and local tax effort [Baretti, Huber and Lichtblau (2000), Von Hagen and Hepp (2000), Jha, Mohanty, Chattergee and Chitkara (1999), Sagbas (2001)]. Although tax revenue is an accurate and observable variable, still one can hardly say that it is a good estimate of tax effort. The reason is for a given region in a given time period tax revenue is affected by many potential variables outside the control of local governments (like idiosyncratic shocks to some specific tax bases) which are seldom well controlled for in estimates of tax capacity. In practice local tax effort encompasses a broad set of actions. One of them is clearly the battle against tax evasion. In spite of its importance, this problem has been only recently addressed by the local public finance literature. Bordignon, Manasse and Tabellini (1996), presented a model where a local government exerts costless effort to catch tax evader workers and they showed how intergovernmental transfers affect tax enforcement. The drawback of this model is that, in reality, tax enforcement is not costless and the cost depends upon other variables chosen by local authorities, like the efficiency of the local tax administration. Although Prud'homme (1995) and Tanzi (1996) have informally signaled the possible inefficiencies of the local tax administrations, this feature has not been raised by the theoretical or the empirical literature. The purpose of this paper is precisely to incorporate such dimension in the assessment of the relationship between intergovernmental transfers and local tax effort. The theoretical framework assumes that in each region there is one representative habitant and a local government. The habitant posses a low or a high-valued property. The local government maximizes tax revenues. In a first period, the local government invests resources to improve the efficiency of the tax administration or to lobby the central government in order to obtain discretionary transfers. This decision is affected by the political cost of reforming the tax administration and on the ability of the local government to negotiate with the central government. Thus, in our model, intergovernmental transfers are endogenous and simultaneously determined with the reform of the local tax system. In a second period, the local government sets the property tax schedule. But, as the local government is unable to observe the value of the property, it has to rely on the habitant announcing this value. Finally, in the third period, the local government decides to enforce the tax law by randomly auditing such announcement. If the habitant is discovered having misreported, the local government sets the corresponding property tax and imposes a penalty. We assume that audit is perfect but costly; the cost depending on the efficiency of the local tax administration. We solve the model backwards. As the local government cannot commit to the auditing probability when it designs its tax policy, the equilibrium of the audit-report game is in mixed strategies, with auditing and tax evasion. Then we find the optimal tax schedule. In order to reduce the stake for tax evasion, the local government distorts downwardly the high-valued property tax. Finally, we solve for the decision of the local government regarding how much resources to invest for improving the efficiency of the tax administration. We find that this decision is negatively associated with the domestic political costs and positively with the ability to negotiate with the Federal Government. The predictions of the model are empirically tested using data for Argentina. The theory suggests a two-step approach. In a first stage we run a probit estimation where the probability of a certain province to reform its tax system (or receiving discretionary transfers) in a given year will be correlated with domestic political variables (e.g. divided government) and also with variables describing its bargaining power vis a vis the federal authorities (e.g. political representation at the National Congress, political party of the President vis a vis that of the Governor). In a second stage, we include this exogenous instrument of tax reform in a regression where the evolution of actual provincial tax receipts are regressed against this variable plus other controls like population, density, provincial income distribution and production structure. Notice that this two stage empirical approach allow us to deal with a frequent problem encountered in the empirical literature given by the endogeneity bias affecting some of the variables of interest, like federal transfers (e.g. Jha, Mohanty, Chattergee and Chitkara (1999), Sagbas (2001)).local tax effort - discretionary transfers - tax enforcement

How to squeeze the toothpaste back into the tube

We consider "bridges" for the simple exclusion process on Z, either symmetric or asymmetric, in which particles jump to the right at rate p and to the left at rate 1-p. The initial state O has all negative sites occupied and all non-negative sites empty. We study the probability that the process is again in state O at time t, and the behaviour of the process on [0,t] conditioned on being in state O at time t. In the case p=1/2, we find that such a bridge typically goes a distance of order t (in the sense of graph distance) from the initial state. For the asymmetric systems, we note an interesting duality which shows that bridges with parameters p and 1-p have the same distribution; the maximal distance of the process from the original state behaves like c(p)log(t) for some constant c(p) depending on p. (For p>1/2, the front particle therefore travels much less far than the bridge of the corresponding random walk, even though in the unconditioned process the path of the front particle dominates a random walk.) We mention various further questions.Comment: 15 page