Dissecting carotenoid from structural components of carotenoid-based coloration: a field experiment with great tits (Parus major).

Carotenoid-based yellowish to red plumage colors are widespread visual signals used in sexual and social communication. To understand their ultimate signaling functions, it is important to identify the proximate mechanism promoting variation in coloration. Carotenoid-based colors combine structural and pigmentary components, but the importance of the contribution of structural components to variation in pigment-based colors (i.e., carotenoid-based colors) has been undervalued. In a field experiment with great tits (Parus major), we combined a brood size manipulation with a simultaneous carotenoid supplementation in order to disentangle the effects of carotenoid availability and early growth condition on different components of the yellow breast feathers. By defining independent measures of feather carotenoid content (absolute carotenoid chroma) and background structure (background reflectance), we demonstrate that environmental factors experienced during the nestling period, namely, early growth conditions and carotenoid availability, contribute independently to variation in yellow plumage coloration. While early growth conditions affected the background reflectance of the plumage, the availability of carotenoids affected the absolute carotenoid chroma, the peak of maximum ultraviolet reflectance, and the overall shape, that is, chromatic information of the reflectance curves. These findings demonstrate that environment-induced variation in background structure contributes significantly to intraspecific variation in yellow carotenoid-based plumage coloration.

Lymphoid environment limits superantigen and antigen-induced T cell proliferation at high precursor frequency.

After superantigen challenge a significant proportion of superantigen-reactive T cells remain undivided. We provide evidence that the lymphoid environment limits T cell proliferation in the secondary lymphoid organs when the frequency of superantigen reactive T cells is unusually high. We monitored T cell proliferation and the percentage of undivided cells when the frequency of superantigen-reactive T cells was low (1%), intermediate (15%) or high (30-100%) by transferring fluorescently labeled cells into different recipients. When the frequency was low, practically all the reactive T cells entered cell cycle and proliferated maximally. At intermediate frequencies a large proportion of reactive T cells did not enter cell cycle and the whole population divided less. A further increase in reactive T cells did not alter the percentage of undivided cells but induced a further decrease in the number of cell divisions. Interestingly, the observations made with superantigens were confirmed with peptide antigen and TCR-transgenic mice. Moreover, in vivo and in vitro data suggest that dendritic cells are the most likely candidates in limiting T cell proliferation in the lymphoid environment. In conclusion, we show that the availability of APC in the lymphoid environment can quantitatively limit T cell priming.

Genetics of decayed sexual traits in a parasitoid wasp with endosymbiont-induced asexuality.

Trait decay may occur when selective pressures shift, owing to changes in environment or life style, rendering formerly adaptive traits non-functional or even maladaptive. It remains largely unknown if such decay would stem from multiple mutations with small effects or rather involve few loci with major phenotypic effects. Here, we investigate the decay of female sexual traits, and the genetic causes thereof, in a transition from haplodiploid sexual reproduction to endosymbiont-induced asexual reproduction in the parasitoid wasp Asobara japonica. We take advantage of the fact that asexual females cured of their endosymbionts produce sons instead of daughters, and that these sons can be crossed with sexual females. By combining behavioral experiments with crosses designed to introgress alleles from the asexual into the sexual genome, we found that sexual attractiveness, mating, egg fertilization and plastic adjustment of offspring sex ratio (in response to variation in local mate competition) are decayed in asexual A. japonica females. Furthermore, introgression experiments revealed that the propensity for cured asexual females to produce only sons (because of decayed sexual attractiveness, mating behavior and/or egg fertilization) is likely caused by recessive genetic effects at a single locus. Recessive effects were also found to cause decay of plastic sex-ratio adjustment under variable levels of local mate competition. Our results suggest that few recessive mutations drive decay of female sexual traits, at least in asexual species deriving from haplodiploid sexual ancestors.

Activation of a dendritic cell-T cell axis by Ad5 immune complexes creates an improved environment for replication of HIV in T cells.

The STEP HIV vaccine trial, which evaluated a replication-defective adenovirus type 5 (Ad5) vector vaccine, was recently stopped. The reasons for this included lack of efficacy of the vaccine and a twofold increase in the incidence of HIV acquisition among vaccinated recipients with increased Ad5-neutralizing antibody titers compared with placebo recipients. To model the events that might be occurring in vivo, the effect on dendritic cells (DCs) of Ad5 vector alone or treated with neutralizing antiserum (Ad5 immune complexes [IC]) was compared. Ad5 IC induced more notable DC maturation, as indicated by increased CD86 expression, decreased endocytosis, and production of tumor necrosis factor and type I interferons. We found that DC stimulation by Ad5 IC was mediated by the Fcgamma receptor IIa and Toll-like receptor 9 interactions. DCs treated with Ad5 IC also induced significantly higher stimulation of Ad5-specific CD8 T cells equipped with cytolytic machinery. In contrast to Ad5 vectors alone, Ad5 IC caused significantly enhanced HIV infection in DC-T cell cocultures. The present results indicate that Ad5 IC activates a DC-T cell axis that, together with the possible persistence of the Ad5 vaccine in seropositive individuals, may set up a permissive environment for HIV-1 infection, which could account for the increased acquisition of HIV-1 infection among Ad5 seropositive vaccine recipients.

Fas ligand-induced apoptosis of infected human macrophages reduces the viability of intracellular Mycobacterium tuberculosis.

Mycobacterium tuberculosis-specific cytolytic activity is mediated mostly by CD4+CTL in humans. CD4+CTL kill infected target cells by inducing Fas (APO-1/CD95)-mediated apoptosis. We have examined the effect of Fas ligand (FasL)-induced apoptosis of human macrophages infected in vitro with M. tuberculosis on the viability of the intracellular bacilli. Human macrophages expressed Fas and underwent apoptosis after incubation with soluble recombinant FasL. In macrophages infected either with an attenuated (H37Ra) or with a virulent (H37Rv) strain of M. tuberculosis, the apoptotic death of macrophages was associated with a substantial reduction in bacillary viability. TNF-induced apoptosis of infected macrophages was coupled with a similar reduction in mycobacterial viability, while the induction of nonapoptotic complement-induced cell death had no effect on bacterial viable counts. Infected macrophages also showed a reduced susceptibility to FasL-induced apoptosis correlating with a reduced level of Fas expression. These data suggest that apoptosis of infected macrophages induced through receptors of the TNF family could be an immune effector mechanism not only depriving mycobacteria from their growth environment but also reducing viable bacterial counts by an unknown mechanism. On the other hand, interference by M. tuberculosis with the FasL system might represent an escape mechanism of the bacteria attempting to evade the effect of apoptosis.

The effect of translocation-induced nuclear reorganization on gene expression.

Translocations are known to affect the expression of genes at the breakpoints and, in the case of unbalanced translocations, alter the gene copy number. However, a comprehensive understanding of the functional impact of this class of variation is lacking. Here, we have studied the effect of balanced chromosomal rearrangements on gene expression by comparing the transcriptomes of cell lines from controls and individuals with the t(11;22)(q23;q11) translocation. The number of differentially expressed transcripts between translocation-carrying and control cohorts is significantly higher than that observed between control samples alone, suggesting that balanced rearrangements have a greater effect on gene expression than normal variation. Many of the affected genes are located along the length of the derived chromosome 11. We show that this chromosome is concomitantly altered in its spatial organization, occupying a more central position in the nucleus than its nonrearranged counterpart. Derivative 22-mapping chromosome 22 genes, on the other hand, remain in their usual environment. Our results are consistent with recent studies that experimentally altered nuclear organization, and indicated that nuclear position plays a functional role in regulating the expression of some genes in mammalian cells. Our study suggests that chromosomal translocations can result in hitherto unforeseen, large-scale changes in gene expression that are the consequence of alterations in normal chromosome territory positioning. This has consequences for the patterns of gene expression change seen during tumorigenesis-associated genome instability and during the karyotype changes that lead to speciation.

Can fisheries-induced evolution shift reference points for fisheries management?

Biological reference points are important tools for fisheries management. Reference points are not static, but may change when a population's environment or the population itself changes. Fisheries-induced evolution is one mechanism that can alter population characteristics, leading to "shifting" reference points by modifying the underlying biological processes or by changing the perception of a fishery system. The former causes changes in "true" reference points, whereas the latter is caused by changes in the yardsticks used to quantify a system's status. Unaccounted shifts of either kind imply that reference points gradually lose their intended meaning. This can lead to increased precaution, which is safe, but potentially costly. Shifts can also occur in more perilous directions, such that actual risks are greater than anticipated. Our qualitative analysis suggests that all commonly used reference points are susceptible to shifting through fisheries-induced evolution, including the limit and "precautionary" reference points for spawning-stock biomass, Blim and Bpa, and the target reference point for fishing mortality, F0.1. Our findings call for increased awareness of fisheries-induced changes and highlight the value of always basing reference points on adequately updated information, to capture all changes in the biological processes that drive fish population dynamics.

The alternatively spliced domain TnFnIII A1A2 of the extracellular matrix protein tenascin-C suppresses activation-induced T lymphocyte proliferation and cytokine production.

Several lines of evidences have suggested that T cell activation could be impaired in the tumor environment, a condition referred to as tumor-induced immunosuppression. We have previously shown that tenascin-C, an extracellular matrix protein highly expressed in the tumor stroma, inhibits T lymphocyte activation in vitro, raising the possibility that this molecule might contribute to tumor-induced immunosuppression in vivo. However, the region of the protein mediating this effect has remained elusive. Here we report the identification of the minimal region of tenascin-C that can inhibit T cell activation. Recombinant fragments corresponding to defined regions of the molecule were tested for their ability to inhibit in vitro activation of human peripheral blood T cells induced by anti-CD3 mAbs in combination with fibronectin or IL-2. A recombinant protein encompassing the alternatively spliced fibronectin type III domains of tenascin-C (TnFnIII A-D) vigorously inhibited both early and late lymphocyte activation events including activation-induced TCR/CD8 down-modulation, cytokine production, and DNA synthesis. In agreement with this, full length recombinant tenascin-C containing the alternatively spliced region suppressed T cell activation, whereas tenascin-C lacking this region did not. Using a series of smaller fragments and deletion mutants issued from this region, we have identified the TnFnIII A1A2 domain as the minimal region suppressing T cell activation. Single TnFnIII A1 or A2 domains were no longer inhibitory, while maximal inhibition required the presence of the TnFnIII A3 domain. Altogether, these data demonstrate that the TnFnIII A1A2 domain mediate the ability of tenascin-C to inhibit in vitro T cell activation and provide insights into the immunosuppressive activity of tenascin-C in vivo.

Antibiotic-induced modifications of the stiffness of bacterial membranes.

In the latest years the importance of high resolution analysis of the microbial cell surface has been increasingly recognized. Indeed, in order to better understand bacterial physiology and achieve rapid diagnostic and treatment techniques, a thorough investigation of the surface modifications induced on bacteria by different environmental conditions or drugs is essential. Several instruments are nowadays available to observe at high resolution specific properties of microscopic samples. Among these, AFM can routinely study single cells in physiological conditions, measuring the mechanical properties of their membrane at a nanometric scale (force volume). Such analyses, coupled with high resolution investigation of their morphological properties, are increasingly used to characterize the state of single cells. In this work we exploit such technique to characterize bacterial systems. We have performed an analysis of the mechanical properties of bacteria (Escherichia coli) exposed to different conditions. Such measurements were performed on living bacteria, by changing in real-time the liquid environment: standard phosphate buffered saline, antibiotic (ampicillin) in PBS and growth medium. In particular we have focused on the determination of the membrane stiffness modifications induced by these solutions, in particular between stationary and replicating phases and what is the effect of the antibiotic on the bacterial structure.

Bacterial-induced protection against allergy through a novel multi-component immunoregulatory mechanism

Airborne microbial products have been reported to promote immune responses that suppress asthma, yet how these beneficial effects take place remains controversial and poorly understood. We have found that pulmonary exposure with the bacterium Escherichia coli leads to a suppression of allergic airway inflammation, characterized by reduced airway-hyperresponsiveness, eosinophilia and cytokine production by T cells in the lung. This immune modulation was neither mediated by the induction of a Th1 response nor regulatory T cells; was dependent on TLR-4 but did not involve TLR-desensitization. Dendritic cell migration to the draining lymph nodes and subsequent activation of T cells was unaffected by prior exposure to E.coli indicating that the immunomodulation was limited to the lung environment. In non-treated control mice ovalbumin was primarily presented by airway CD11b+ CD11c+ DCs expressing high levels of MHC class II molecules whilst the DCs in E.coli-treated mice displayed a less activated phenotype and had impaired antigen presentation capacity. Consequently, in situ Th2 cytokine production by ovalbuminspecific effector T cells recruited to the airways was significantly reduced. The suppression of airways hyper responsiveness was mediated through the recruitment of IL-17-producing gd-T cells; however, the suppression of dendritic cells and T cells was mediated through a distinct mechanism that could not be overcome by the local administration of activated dendritic cells, or by the in vivo administration of TNF-alpha. Taken together, these data reveal a novel multi-component immunoregulatory pathway that acts to protect the airways from allergic inflammation.

Looking for orders of magnitude : five essays in trade and the environment and economic geography

General Summary Although the chapters of this thesis address a variety of issues, the principal aim is common: test economic ideas in an international economic context. The intention has been to supply empirical findings using the largest suitable data sets and making use of the most appropriate empirical techniques. This thesis can roughly be divided into two parts: the first one, corresponding to the first two chapters, investigates the link between trade and the environment, the second one, the last three chapters, is related to economic geography issues. Environmental problems are omnipresent in the daily press nowadays and one of the arguments put forward is that globalisation causes severe environmental problems through the reallocation of investments and production to countries with less stringent environmental regulations. A measure of the amplitude of this undesirable effect is provided in the first part. The third and the fourth chapters explore the productivity effects of agglomeration. The computed spillover effects between different sectors indicate how cluster-formation might be productivity enhancing. The last chapter is not about how to better understand the world but how to measure it and it was just a great pleasure to work on it. "The Economist" writes every week about the impressive population and economic growth observed in China and India, and everybody agrees that the world's center of gravity has shifted. But by how much and how fast did it shift? An answer is given in the last part, which proposes a global measure for the location of world production and allows to visualize our results in Google Earth. A short summary of each of the five chapters is provided below. The first chapter, entitled "Unraveling the World-Wide Pollution-Haven Effect" investigates the relative strength of the pollution haven effect (PH, comparative advantage in dirty products due to differences in environmental regulation) and the factor endowment effect (FE, comparative advantage in dirty, capital intensive products due to differences in endowments). We compute the pollution content of imports using the IPPS coefficients (for three pollutants, namely biological oxygen demand, sulphur dioxide and toxic pollution intensity for all manufacturing sectors) provided by the World Bank and use a gravity-type framework to isolate the two above mentioned effects. Our study covers 48 countries that can be classified into 29 Southern and 19 Northern countries and uses the lead content of gasoline as proxy for environmental stringency. For North-South trade we find significant PH and FE effects going in the expected, opposite directions and being of similar magnitude. However, when looking at world trade, the effects become very small because of the high North-North trade share, where we have no a priori expectations about the signs of these effects. Therefore popular fears about the trade effects of differences in environmental regulations might by exaggerated. The second chapter is entitled "Is trade bad for the Environment? Decomposing worldwide SO2 emissions, 1990-2000". First we construct a novel and large database containing reasonable estimates of SO2 emission intensities per unit labor that vary across countries, periods and manufacturing sectors. Then we use these original data (covering 31 developed and 31 developing countries) to decompose the worldwide SO2 emissions into the three well known dynamic effects (scale, technique and composition effect). We find that the positive scale (+9,5%) and the negative technique (-12.5%) effect are the main driving forces of emission changes. Composition effects between countries and sectors are smaller, both negative and of similar magnitude (-3.5% each). Given that trade matters via the composition effects this means that trade reduces total emissions. We next construct, in a first experiment, a hypothetical world where no trade happens, i.e. each country produces its imports at home and does no longer produce its exports. The difference between the actual and this no-trade world allows us (under the omission of price effects) to compute a static first-order trade effect. The latter now increases total world emissions because it allows, on average, dirty countries to specialize in dirty products. However, this effect is smaller (3.5%) in 2000 than in 1990 (10%), in line with the negative dynamic composition effect identified in the previous exercise. We then propose a second experiment, comparing effective emissions with the maximum or minimum possible level of SO2 emissions. These hypothetical levels of emissions are obtained by reallocating labour accordingly across sectors within each country (under the country-employment and the world industry-production constraints). Using linear programming techniques, we show that emissions are reduced by 90% with respect to the worst case, but that they could still be reduced further by another 80% if emissions were to be minimized. The findings from this chapter go together with those from chapter one in the sense that trade-induced composition effect do not seem to be the main source of pollution, at least in the recent past. Going now to the economic geography part of this thesis, the third chapter, entitled "A Dynamic Model with Sectoral Agglomeration Effects" consists of a short note that derives the theoretical model estimated in the fourth chapter. The derivation is directly based on the multi-regional framework by Ciccone (2002) but extends it in order to include sectoral disaggregation and a temporal dimension. This allows us formally to write present productivity as a function of past productivity and other contemporaneous and past control variables. The fourth chapter entitled "Sectoral Agglomeration Effects in a Panel of European Regions" takes the final equation derived in chapter three to the data. We investigate the empirical link between density and labour productivity based on regional data (245 NUTS-2 regions over the period 1980-2003). Using dynamic panel techniques allows us to control for the possible endogeneity of density and for region specific effects. We find a positive long run elasticity of density with respect to labour productivity of about 13%. When using data at the sectoral level it seems that positive cross-sector and negative own-sector externalities are present in manufacturing while financial services display strong positive own-sector effects. The fifth and last chapter entitled "Is the World's Economic Center of Gravity Already in Asia?" computes the world economic, demographic and geographic center of gravity for 1975-2004 and compares them. Based on data for the largest cities in the world and using the physical concept of center of mass, we find that the world's economic center of gravity is still located in Europe, even though there is a clear shift towards Asia. To sum up, this thesis makes three main contributions. First, it provides new estimates of orders of magnitudes for the role of trade in the globalisation and environment debate. Second, it computes reliable and disaggregated elasticities for the effect of density on labour productivity in European regions. Third, it allows us, in a geometrically rigorous way, to track the path of the world's economic center of gravity.

Manipulating the sensitivity of signal-induced repression: quantification and consequences of altered brinker gradients.

Traditionally, the analysis of gene regulatory regions suffered from the caveat that it was restricted to artificial contexts (e.g. reporter constructs of limited size). With the advent of the BAC recombineering technique, genomic constructs can now be generated to test regulatory elements in their endogenous environment. The expression of the transcriptional repressor brinker (brk) is negatively regulated by Dpp signaling. Repression is mediated by small sequence motifs, the silencer elements (SEs), that are present in multiple copies in the regulatory region of brk. In this work, we manipulated the SEs in the brk locus. We precisely quantified the effects of the individual SEs on the Brk gradient in the wing disc by employing a 1D data extraction method, followed by the quantification of the data with reference to an internal control. We found that mutating the SEs results in an expansion of the brk expression domain. However, even after mutating all predicted SEs, repression could still be observed in regions of maximal Dpp levels. Thus, our data point to the presence of additional, low affinity binding sites in the brk locus.

Loss of glucose-induced insulin secretion and GLUT2 expression in transplanted beta-cells.

Either 200 or 400 syngeneic islets were transplanted under the kidney capsule of normal or streptozocin-induced diabetic B6/AF1 mice. The diabetic mice with 400 islets became normoglycemic, but those with 200 islets, an insufficient number, were still diabetic after the transplantation (Tx). Two weeks after Tx, GLUT2 expression in the islet grafts was evaluated by immunofluorescence and Western blots, and graft function was examined by perfusion of the graft-bearing kidney. Immunofluorescence for GLUT2 was dramatically reduced in the beta-cells of grafts with 200 islets exposed to hyperglycemia. However, it was plentiful in grafts with 400 islets in a normoglycemic environment. Densitometric analysis of Western blots on graft homogenates demonstrated that GLUT2 protein levels in the islets, when exposed to chronic hyperglycemia for 2 weeks, were decreased to 16% of those of normal recipients. Moreover, these grafts had defective glucose-induced insulin secretion, while the effects of arginine were preserved. We conclude that GLUT2 expression in normal beta-cells is promptly down-regulated during exposure to hyperglycemia and may contribute to the loss of glucose-induced secretion of diabetes.

Phenotypic plasticity in salmonid embryos : characterizing pathogen-induced stress effects on heritable variation in traits and reaction norms

Les pressions écologiques peuvent varier tant en nature qu'en intensité dans le temps et l'espace. C'est pourquoi, un phénotype unique ne peut pas forcément conférer la meilleure valeur sélective. La plasticité phénotypique peut être un moyen de s'accommoder de cette situation, en augmentant globalement la tolérance aux changements environnementaux. Comme pour tout trait de caractère, une variation génétique doit persister pour qu'évoluent les traits plastiques dans une population donnée. Cependant, les pressions extérieures peuvent affecter l'héritabilité, et la direction de ces changements peut dépendre du caractère en question, de l'espèce mais aussi du type de stress. Dans la présente thèse, nous avons cherché à élucider les effets des pressions pathogéniques sur les phénotypes et la génétique quantitative de plusieurs traits plastiques chez les embryons de deux salmonidés, la palée (Coregonus palaea), et la truite de rivière (Salmo trutta). Les salmonidés se prêtent à de telles études du fait de leur extraordinaire variabilité morphologique, comportementale et des traits d'histoire de vie. Par ailleurs, avec le déclin des salmonidés dans le monde, il est important de savoir combien la variabilité génétique persiste dans les normes de réaction afin d'aider à prédire leur capacité à répondre aux changements de leur milieu. Nous avons observé qu'une augmentation de la croissance des communautés microbiennes symbiotiques entraînait une mortalité accrue et une éclosion précoce chez la palée, et dévoilait la variance génétique additive pour ces deux caractères (Chapitres 1-2). Bien qu'aucune variation génétique n'ait été trouvée pour les normes de réaction, nous avons observé une variabilité de la plasticité d'éclosion. Néanmoins, on a trouvé que les temps d'éclosion étaient corrélés entre les environnements, ce qui pourrait limiter l'évolution de la norme de réaction. Le temps d'éclosion des embryons est lié à la taille des géniteurs mâles, ce qui indique des effets pléiotropiques. Dans le Chapitre 3, nous avons montré qu'une interaction triple entre la souche bactérienne {Pseudomonas fluorescens}, l'état de dévelopement de l'hôte ainsi que ses gènes ont une influence sur la mortalité, le temps d'éclosion et la taille des alevins de la palée. Nous avons démontré qu'une variation génétique subsistait généralement dans les normes de réaction des temps d'éclosion, mais rarement pour la taille des alevins, et jamais pour la mortalité. Dans le même temps, nous avons exhibé que des corrélations entre environnements dépendaient des caractères phénotypiques, mais contrairement au Chapitre 2, nous n'avons pas trouvé de preuve de corrélations transgénérationnelles. Le Chapitre 4 complète le chapitre précédent, en se plaçant du point de vue moléculaire, et décrit comment le traitement d'embryons avec P. fluorescens s'est traduit par une régulation négative d'expression du CMH-I indépendemment de la souche bactérienne. Nous avons non seulement trouvé une variation génétique des caractères phénotypiques moyens, mais aussi de la plasticité. Les deux derniers chapitres traitent de l'investigation, chez la truite de rivière, des différences spécifiques entre populations pour des normes de réaction induites par les pathogènes. Dans le Chapitre 5, nous avons illustré que le métissage entre des populations génétiquement distinctes n'affectait en rien la hauteur ou la forme des normes de réaction d'un trait précoce d'histoire de vie suite au traitement pathogénique. De surcroît, en dépit de l'éclosion tardive et de la réduction de la taille des alevins, le traitement n'a pas modifié la variation héritable des traits de caractère. D'autre part, dans le Chapitre 6, nous avons démontré que le traitement d'embryons avec des stimuli contenus dans l'eau de conspécifiques infectés a entraîné des réponses propre à chaque population en terme de temps d'éclosion ; néanmoins, nous avons observé peu de variabilité génétique des normes de réaction pour ce temps d'éclosion au sein des populations. - Ecological stressors can vary in type and intensity over space and time, and as such, a single phenotype may not confer the highest fitness. Phenotypic plasticity can act as a means to accommodate this situation, increasing overall tolerance to environmental change. As with any trait, for plastic traits to evolve in a population, genetic variation must persist. However, environmental stress can alter trait heritability, and the direction of this shift can be trait, species, and stressor-dependent. In this thesis, we sought to understand the effects of pathogen stressors on the phenotypes and genetic architecture of several plastic traits in the embryos of two salmonids, the whitefish (Coregonus palaea), and the brown trout (Salmo trutta). Salmonids lend themselves to such studies because their extraordinary variability in morphological, behavioral, and life-history traits. Also, with declines in salmonids worldwide, knowing how much genetic variability persists in reaction norms may help predict their ability to respond to environmental change. We found that increasing growth of symbiotic microbial communities increased mortality and induced hatching in whitefish, and released additive genetic variance for both traits (Chapters 1-2). While no genetic variation was found for survival reaction norms, we did find variability in hatching plasticity. Nevertheless, hatching time was correlated across environments, which could constrain evolution of the reaction norm. Hatching time in the induced environment was also correlated to sire size, indicating pleiotropic effects. In Chapter 3 we report that a three-way interaction between bacterial strain (Pseudomonas fluorescens), host developmental stage, and host genetics impacted mortality, hatching time, and hatchling size in whitefish. We also showed that genetic variation generally persisted in hatching age reaction norms, but rarely for hatchling length, and never for mortality. At the same time, we demonstrated that cross-environmental correlations were trait-dependent, and unlike Chapter 2, we found no evidence of cross-generational correlations. Chapter 4 expands on the previous chapter, moving to the molecular level, and describes how treatment of embryos with P. fluorescens resulted in strain-independent downregulation of MHC class I. Genetic variation was evident not only in trait means, but also in plasticity. In the last two chapters, we investigated population level differences in pathogen- induced reaction norms in brown trout. In Chapter 5, we found that interbreeding between genetically distinct populations did not affect the elevation or shapes of the reaction norms of early life-history traits after pathogen challenge. Moreover, despite delaying hatching and reducing larval length, treatment produced no discernable shifts in heritable variation in traits. On the other hand, in Chapter 6, we found that treatment of embryos with water-borne cues from infected conspecifics elicited population-specific responses in terms of hatching time; however, we found little evidence of genetic variability in hatching reaction norms within populations. We have made considerable progress in understanding how pathogen stressors affect various early life-history traits in salmonid embryos. We have demonstrated that the effect of a particular stressor on heritable variation in these traits can vary according to the trait and species under consideration, in addition to the developmental stage of the host. Moreover, we found evidence of genetic variability in some, but not all reaction norms in whitefish and brown trout.

Cutting edge: cell autonomous rather than environmental factors control bacterial superantigen-induced T cell anergy in vivo.

Anergic T cells display a marked decrease in their ability to produce IL-2 and to proliferate in the presence of an appropriate antigenic signal. Two nonmutually exclusive classes of models have been proposed to explain the persistence of T cell anergy in vivo. While some reports indicate that anergic T cells have intrinsic defects in signaling pathways or transcriptional activities, other studies suggest that anergy is maintained by environmental "suppressor" factors such as cytokines or Abs. To distinguish between these conflicting hypotheses, we employed the well-characterized bacterial superantigen model system to evaluate in vivo the ability of a trace population of adoptively transferred naive or anergized T cells to proliferate in a naive vs anergic environment upon subsequent challenge. Our data clearly demonstrate that bacterial superantigen-induced T cell anergy is cell autonomous and independent of environmental factors.