Fruit flies learn to avoid odours associated with virulent infection.

While learning to avoid toxic food is common in mammals and occurs in some insects, learning to avoid cues associated with infectious pathogens has received little attention. We demonstrate that Drosophila melanogaster show olfactory learning in response to infection with their virulent intestinal pathogen Pseudomonas entomophila. This pathogen was not aversive to taste when added to food. Nonetheless, flies exposed for 3 h to food laced with P. entomophila, and scented with an odorant, became subsequently less likely to choose this odorant than flies exposed to pathogen-laced food scented with another odorant. No such effect occurred after an otherwise identical treatment with an avirulent mutant of P. entomophila, indicating that the response is mediated by pathogen virulence. These results demonstrate that a virulent pathogen infection can act as an aversive unconditioned stimulus which flies can associate with food odours, and thus become less attracted to pathogen-contaminated food.

Speed-cohesion trade-offs in collective decision making in ants and the concept of precision in animal behaviour

In decision making, speed-accuracy trade-offs are well known and often inevitable because accuracy depends on being well informed and gathering information takes time. However, trade-offs between speed and cohesion, that is the degree to which a group remains together as a single entity, as a result of their decision making, have been comparatively neglected. We combine theory and experimentation to show that in decision-making systems, speed-cohesion trade-offs are a natural complement to speed-accuracy trade-offs and are therefore of general importance. We then analyse the decision performance of 32 rock ant, Temnothorax albipennis, colonies in experiments in which accuracy of collective decision making was held constant, but time urgency varied. These experiments reveal for the first time an adaptive speed-cohesion trade-off in collective decision making and how this is achieved. In accord with different time constraints, colonies can decide quickly, at the cost of social unity, or they can decide slowly with much greater cohesion. We discuss the similarity between cohesion and the term precision as used in statistics and engineering. This emphasizes the generality of speed versus cohesion/precision trade-offs in decision making and decision implementation in other fields within animal behaviour such as sexually selected motor displays and even certain aspects of birdsong. We also suggest that speed versus precision trade-offs may occur when individuals within a group need to synchronize their activity, and in collective navigation, cooperative hunting and in certain escape behaviours.

The Spatial Effects of Trade Openness: A Survey

This paper surveys the literature on the implications of trade liberalisation for intra-national economic geographies. Three results stand out. First, neither urban systems models nor new economic geography models imply a robust prediction for the impact of trade openness on spatial concentration. Whether trade promotes concentration or dispersion depends on subtle modelling choices among which it is impossible to adjudicate a priori. Second, empirical evidence mirrors the theoretical indeterminacy: a majority of cross-country studies find no significant effect of openness on urban concentration or regional inequality. Third, the available models predict that, other things equal, regions with inherently less costly access to foreign markets, such as border or port regions, stand to reap the largest gains from trade liberalisation. This prediction is confirmed by the available evidence. Whether trade liberalisation raises or lowers regional inequality therefore depends on each country's specific geography.

Trade-off between constitutive and inducible resistance against herbivores is only partially explained by gene expression and glucosinolate production.

The hypothesis that constitutive and inducible plant resistance against herbivores should trade-off because they use the same resources and impose costs to plant fitness has been postulated for a long time. Negative correlations between modes of deployment of resistance and defences have been observed across and within species in common garden experiments. It was therefore tested whether that pattern of resistance across genotypes follows a similar variation in patterns of gene expression and chemical defence production. Using the genetically tractable model Arabidopsis thaliana and different modes of induction, including the generalist herbivore Spodoptera littoralis, the specialist herbivore Pieris brassicae, and jasmonate application, constitutive and inducibility of resistance was measured across seven A. thaliana accessions that were previously selected based on constitutive levels of defence gene expression. According to theory, it was found that modes of resistance traded-off among accessions, particularly against S. littoralis, in which accessions investing in high constitutive resistance did not increase it substantially after attack and vice-versa. Accordingly, the average expression of eight genes involved in glucosinolate production negatively predicted larval growth across the seven accessions. Glucosinolate production and genes related to defence induction on healthy and herbivore-damaged plants were measured next. Surprisingly, only a partial correlation between glucosinolate production, gene expression, and the herbivore resistance results was found. These results suggest that the defence outcome of plants against herbivores goes beyond individual molecules or genes but stands on a complex network of interactions.

Discovery-dominance trade-off among widespread invasive ant species

Ants are among the most problematic invasive species. They displace numerous native species, alter ecosystem processes, and can have negative impacts on agriculture and human health. In part, their success might stem from a departure from the discovery-dominance trade-off that can promote co-existence in native ant communities, that is, invasive ants are thought to be at the same time behaviorally dominant and faster discoverers of resources, compared to native species. However, it has not yet been tested whether similar asymmetries in behavioral dominance, exploration, and recruitment abilities also exist among invasive species. Here, we establish a dominance hierarchy among four of the most problematic invasive ants (Linepithema humile, Lasius neglectus, Wasmannia auropunctata, Pheidole megacephala) that may be able to arrive and establish in the same areas in the future. To assess behavioral dominance, we used confrontation experiments, testing the aggressiveness in individual and group interactions between all species pairs. In addition, to compare discovery efficiency, we tested the species' capacity to locate a food resource in a maze, and the capacity to recruit nestmates to exploit a food resource. The four species differed greatly in their capacity to discover resources and to recruit nestmates and to dominate the other species. Our results are consistent with a discovery-dominance trade-off. The species that showed the highest level of interspecific aggressiveness and dominance during dyadic interactions.

Fruit and vegetables and cancer risk : a review of southern European studies

High intakes of fruit and vegetables may reduce the risk of cancer at several sites. Evidence has been derived mainly from case-control studies. We reviewed the relationship between consumption of vegetables and fruit and the risk of several common cancers in a network of Italian and Swiss case-control studies including over 10 000 cases of fourteen different cancers and about 17 000 controls. Data were suggestive of a protective role of vegetable intake on the risk of several common epithelial cancers. OR for the highest compared with the lowest levels of consumption ranged from 0·2 (larynx, oral cavity and pharynx) to 0·9 (prostate). Inverse associations were found for both raw and cooked vegetables, although for upper digestive tract cancers the former were somewhat stronger. Similar inverse associations were found for cruciferous vegetables. Frequent consumption of allium vegetables was also associated with reduced risk of several cancers. Fruit was a favourable correlate of the risk of several cancers, particularly of the upper digestive tract, with associations generally weaker than those reported for vegetables. A reduced risk of cancers of the digestive tract and larynx was found for high consumption of citrus fruit. Suggestive protections against several forms of cancer, mainly digestive tract cancers, were found for high consumption of apples and tomatoes. High intakes of fibres, flavonoids and proanthocyanidins were inversely related to various forms of cancer. In conclusion, data from our series of case-control studies suggested a favourable role of high intakes of fruit and vegetables in the risk of many common cancers, particularly of the digestive tract. This adds evidence to the indication that aspects of the Mediterranean diet may have a favourable impact not only on CVD, but also on several common (epithelial) cancers, particularly of the digestive tract.

Associations between fruit and vegetable consumption and psychological distress: results from a population-based study.

BACKGROUND: Several studies observed associations of various aspects of diet with mental health, but little is known about the relationship between following the 5-a-day recommendation for fruit and vegetables consumption and mental health. Thus, we examined the associations of the Swiss daily recommended fruit and vegetable intake with psychological distress. METHODS: Data from 20,220 individuals aged 15+ years from the 2012 Swiss Health Survey were analyzed. The recommended portions of fruit and vegetables per day were defined as 5-a-day (at least 2 portions of fruit and 3 of vegetables). The outcome was perceived psychological distress over the previous 4 weeks (measured by the 5-item mental health index [MHI-5]). High distress (MHI-5 score ≤ 52), moderate distress (MHI-5 > 52 and ≤ 72) and low distress (MHI-5 > 72 and ≤ 100) were differentiated and multinomial logistic regression analyses adjusted for known confounding factors were performed. RESULTS: The 5-a-day recommendation was met by 11.6 % of the participants with low distress, 9.3 % of those with moderate distress, and 6.2 % of those with high distress. Consumers fulfilling the 5-a-day recommendation had lower odds of being highly or moderately distressed than individuals consuming less fruit and vegetables (moderate vs. low distress: OR = 0.82, 95 % confidence interval [CI] 0.69-0.97; high vs. low distress: OR = 0.55, 95 % CI 0.41-0.75). CONCLUSIONS: Daily intake of 5 servings of fruit and vegetable was associated with lower psychological distress. Longitudinal studies are needed to further determine the causal nature of this relationship.

Gut physiology mediates a trade-off between adaptation to malnutrition and susceptibility to food-borne pathogens.

The animal gut plays a central role in tackling two common ecological challenges, nutrient shortage and food-borne parasites, the former by efficient digestion and nutrient absorption, the latter by acting as an immune organ and a barrier. It remains unknown whether these functions can be independently optimised by evolution, or whether they interfere with each other. We report that Drosophila melanogaster populations adapted during 160 generations of experimental evolution to chronic larval malnutrition became more susceptible to intestinal infection with the opportunistic bacterial pathogen Pseudomonas entomophila. However, they do not show suppressed immune response or higher bacterial loads. Rather, their increased susceptibility to P. entomophila is largely mediated by an elevated predisposition to loss of intestinal barrier integrity upon infection. These results may reflect a trade-off between the efficiency of nutrient extraction from poor food and the protective function of the gut, in particular its tolerance to pathogen-induced damage.

Three Essays on International Trade and the Labor Market

The thesis is made of three independent chapters interested in the impact of globalization on workers in industrialized countries. The dissertation is especially focused on identifying the causal impact of international trade on workers' mobility, wages, and employment with both a short- and medium-term perspective. The first paper explores the relation between intra-industry trade (IIT) expansion and associated worker flows, taking the latter as an indicator of labor-market adjustment costs. Being the first study to combine theoretical simulations and a novel identification strategy, we find that both theoretical and empirical analyses are consistent with the "smooth adjustment hypothesis", according to which IIT expansion is less disruptive than inter-industry trade expansion. The study therefore lends support to the use of IIT indices as first-pass proxies for the adjustment effects of trade expansion. The second chapter contrasts the impact of increased import competition coming from China and the European Union (EU) on workers in the United Kingdom over a 15-year period. The most salient findings show that increased imports from China had significantly negative effects on workers' earnings, wages and employment. In contrast, larger imports from the EU are associated with positive worker-level outcomes, which is largely explained by the fact that increased imports from the EU were mostly offset by increased same-industry exports to the EU. Besides, we find that increased imports from China exert additional pressure on workers through spillovers to employment and wages in downstream industries. Finally, the last chapter is focused on the impact of exposure to trade and real exchange rate shocks on wages for Swiss manufacturing workers. A particular attention is made to consistently estimate the causal effect in using a two-step gravity-type identification strategy. The study shows that the impact of trade and exchange rate movements is concentrated among high-skilled workers almost exclusively.