RICH DYNAMICS OF A SIMPLE SI MODEL WITH TWO AGE GROUPS

The objective of this paper is to study the global dynamics of a simple SI model with two explicit age groups. We divide the population into juvenile and adult groups. Only adults are assumed to be sexually active and we implicitly assume that the sex ratio is constant. We also assume that infected adults may produce both susceptible newborns and infected newborns. We show that such models can produce the often observed and feared scenario of susceptible extinction. This suggests that age structure alone will not remove the total extinction dynamics in a typical ratio-dependent predator-prey model. An important feature of our work is that our analytical results are all presented in terms of the biologically meaningful threshold values

In the Face of Fear, Rebellion (Liv., IV 49, 7-50)

This work aims to show that the Livian text of the patrician M Postumius Regillensis was created as an exemplary tale with the intention of offering a moral lesson on the political concept of moderation moderatio Through the configuration of the bad ruler who acts based on emotions such as anger the author illustrates the fatal consequences for the ruler himself as well as for those ruled by him who let themselves be dragged by similar emotion

Neural Mechanisms that Control an Innate Foraging Behavior in Caenorhabditis Elegans

The ability to efficiently locate food is critical for survival. Thus, animals modify their foraging patterns based on recent experience and current conditions to increase their likelihood of finding food. One highly conserved foraging strategy is local search, an intensive exploration over several minutes of the region where food resources were last encountered. As time since the last food encounter passes, animals transition to global search strategies to explore distant areas. The local-to-global search foraging pattern has been observed in fish, reptiles, insects, birds, and mammals, yet few studies ask how an animal’s brain generates this ancient behavior. Here, I ask this question in the nematode Caenorhabditis elegans. In Chapter 1, I characterize the behavior in wildtype animals and find that local search is a food memory that is regulated by food history and by internal satiety states. In addition, I describe the behavior in individual animals and find that although the behavior is reliable at a population level, there is large variability between individuals. In Chapter 2, I conduct a candidate genetic screen to first find a gene important for local search, and then define a circuit for local search behavior. The circuit consists of two parallel multimodal circuit modules that control local search. In each module, chemosensory or mechanosensory glutamatergic neurons that detect food-related cues trigger local search by inhibiting separate integrating neurons through a metabotropic glutamate receptor, MGL-1. The chemosensory and mechanosensory modules are separate and redundant, as glutamate release from either can drive the full behavior. In addition, the ability of the sensory modules to control local search is gated by the internal nutritional state of the animal. In Chapter 3, I characterize neuronal activity within the chemosensory module. Spontaneous activity patterns in the chemosensory module encode information about the time since the last food encounter and correlate with the foraging behavior. Glutamate acts within the module to shape activity patterns at various time scales. Taken together, these experiments reveal a circuit configuration that allows for the robust control of an innate adaptive behavior

Mapping of the Tacaribe Arenavirus Z-Protein Binding Sites on the L Protein Identified both Amino Acids within the Putative Polymerase Domain and a Region at the N Terminus of L That Are Critically Involved in Binding

Tacaribe virus (TacV) is the prototype of the New World group of arenaviruses. The TacV genome encodes four proteins: the nucleoprotein (N), the glycoprotein precursor, the polymerase (L), and a RING finger protein (Z). Using a reverse genetics system, we demonstrated that TacV N and L are sufficient to drive transcription and replication mediated by TacV-like RNAs and that Z is a powerful inhibitor of these processes (Lopez et al., J. Virol. 65:12241-12251, 2001). More recently, we provided the first evidence of an interaction between Z and L and showed that Z's inhibitory activity was dependent on its ability to bind to L (Jácamo et al., J. Virol. 77:10383-10393, 2003). In the present study, we mapped the TacV Z-binding sites on the 2,210-amino-acid L polymerase. To that end, we performed deletion analysis and point mutations of L and studied the Z-L interaction by coimmunoprecipitation with specific sera. We found that the C-terminal region of L was not essential for the interaction and identified two noncontiguous regions that were critical for binding: one at the N-terminus of L between residues 156 and 292 and a second one in the polymerase domain (domain III). The importance of domain III in binding was revealed by substitutions in D1188 and H1189 within motif A and in each residue of the conserved SDD sequence (residues 1328, 1329, and 1330) within motif C. Our results showed that of the substituted residues, only H1189 and D1329 appeared to be critically involved in binding Z.Fil: Wilda, Maximiliano. Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica. Departamento de Microbiología, Inmunología y Biotecnología. Cátedra de Genética y Biología Molecular; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Lopez, Nora Mabel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Ciencia y Tecnología "Dr. César Milstein"; ArgentinaFil: Casabona, Juan Cruz. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Ciencia y Tecnología "Dr. César Milstein"; ArgentinaFil: Franze Fernandez, Maria T.. Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica. Departamento de Microbiología, Inmunología y Biotecnología. Cátedra de Genética y Biología Molecular; Argentin