Fungal infection alters collective nutritional intake of ant colonies.

In animals, parasitic infections impose significant fitness costs.1,2,3,4,5,6 Infected animals can alter their feeding behavior to resist infection,7,8,9,10,11,12 but parasites can manipulate animal foraging behavior to their own benefits.13,14,15,16 How nutrition influences host-parasite interactions is not well understood, as studies have mainly focused on the host and less on the parasite.9,12,17,18,19,20,21,22,23 We used the nutritional geometry framework24 to investigate the role of amino acids (AA) and carbohydrates (C) in a host-parasite system: the Argentine ant, Linepithema humile, and the entomopathogenic fungus, Metarhizium brunneum. First, using 18 diets varying in AA:C composition, we established that the fungus performed best on the high-amino-acid diet 1:4. Second, we found that the fungus reached this optimal diet when given various diet pairings, revealing its ability to cope with nutritional challenges. Third, we showed that the optimal fungal diet reduced the lifespan of healthy ants when compared with a high-carbohydrate diet but had no effect on infected ants. Fourth, we revealed that infected ant colonies, given a choice between the optimal fungal diet and a high-carbohydrate diet, chose the optimal fungal diet, whereas healthy colonies avoided it. Lastly, by disentangling fungal infection from host immune response, we demonstrated that infected ants foraged on the optimal fungal diet in response to immune activation and not as a result of parasite manipulation. Therefore, we revealed that infected ant colonies chose a diet that is costly for survival in the long term but beneficial in the short term-a form of collective self-medication.

Photosynthetic performance under adaxial and abaxial illumination in three Mediterranean Quercus species differing in branch architecture and individual leaf area.

Light availability effects on canopy-level carbon balance constitute an especially difficult issue to address, owing to the strong spatial and temporal changes of the light environment within the canopy. One of the least explored aspects in relation to light environment is the interaction between leaf angle and leaf anatomy. The inclination of the leaf may affect the distribution of light between the adaxial and abaxial surface. The purpose of this study is determining the proportions of the leaf area receiving light from the abaxial side in branches of isolated trees in three Mediterranean oaks, as well as the photosynthetic responses to light under adaxial and abaxial illumination. The proportions of the leaf area illuminated from below were low for sun incidence angles near 0° with respect to the main axis of the branch. However, for sun incidence angles about 45°, the proportion of leaves receiving abaxial illumination was considerable. PPFD levels on the sunlit part of the abaxial surface were always lower than those in the upper leaf side, as a consequence of the lower projection efficiency for the leaves facing the sun by the lower side. Light absorptance was also lower on the abaxial side. The differences between both sides of the leaf tended to be stronger for thicker, longer-living leaves. We conclude that mean C assimilation of the canopy is significantly decreased by the presence of leaves facing the sun by the lower side and that this decrease is stronger in evergreen species with thicker leaves.

Caenorhabditis elegans foraging patterns follow a simple rule of thumb.

Rules of thumb are behavioral algorithms that approximate optimal behavior while lowering cognitive and sensory costs. One way to reduce these costs is by simplifying the representation of the environment: While the theoretically optimal behavior may depend on many environmental variables, a rule of thumb may use a smaller set of variables that performs reasonably well. Experimental proof of this simplification requires an exhaustive mapping of all relevant combinations of several environmental parameters, which we performed for Caenorhabditis elegans foraging by covering systematically combinations of food density (across 4 orders of magnitude) and food type (across 12 bacterial strains). We found that worms' response is dominated by a single environmental variable: food density measured as number of bacteria per unit surface. They disregard other factors such as biomass content or bacterial strain. We also measured experimentally the impact on fitness of each type of food, determining that the rule is near-optimal and therefore constitutes a rule of thumb that leverages the most informative environmental variable. These results set the stage for further investigations into the underlying genetic and neural mechanisms governing this simplification process, and into its role in the evolution of decision-making strategies.

Branch architecture in relation to canopy positions in three Mediterranean oaks.

Branch architecture is a key determinant of plant performance owing to its role in a light interception by photosynthetic tissues. However, under stressed conditions, excess light may be harmful to the photosynthetic apparatus, and plants often present structural mechanisms to avoid photoinhibition. Three-dimensional models were constructed of the aerial parts in different locations within the crown of three co-occurring tree species (Quercus ilex, Q. suber and Q. faginea) growing in a Mediterranean environment. We hypothesized that the species with the shorter leaf life span would exhibit higher leaf display efficiency (silhouette to total leaf area, STAR), maximizing light interception and photosynthesis in the short term. In addition, more exposed positions within a canopy should develop more structural avoidance mechanisms to minimize excessive radiation. Significant differences were detected in architectural traits at both the intra- and interspecific level. Architectural traits promoting greater self-shading were more frequent in the species with longer leaf longevity and in the canopy locations experiencing higher temperatures at the times of maximum sunlight. However, these trends were in part counteracted by the changes in individual leaf area, which tended to be larger in the species with shorter leaf longevity and in the less exposed canopy locations. We conclude that the variation in architectural traits occurs mainly as a means to avoid the excessive self-shading of branches with the largest leaf size.

Modeling bee movement shows how a perceptual masking effect can influence flower discovery.

Understanding how pollinators move across space is key to understanding plant mating patterns. Bees are typically assumed to search for flowers randomly or using simple movement rules, so that the probability of discovering a flower should primarily depend on its distance to the nest. However, experimental work shows this is not always the case. Here, we explored the influence of flower size and density on their probability of being discovered by bees by developing a movement model of central place foraging bees, based on experimental data collected on bumblebees. Our model produces realistic bee trajectories by taking into account the autocorrelation of the bee's angular speed, the attraction to the nest (homing), and a gaussian noise. Simulations revealed a « masking effect ¼ that reduces the detection of flowers close to another, with potential far reaching consequences on plant-pollinator interactions. At the plant level, flowers distant to the nest were more often discovered by bees in low density environments. At the bee colony level, foragers found more flowers when they were small and at medium densities. Our results indicate that the processes of search and discovery of resources are potentially more complex than usually assumed, and question the importance of resource distribution and abundance on bee foraging success and plant pollination.

The motor Wisdom of the Crowd.

Wisdom of the Crowd is the aggregation of many individual estimates to obtain a better collective one. Because of its enormous social potential, this effect has been thoroughly investigated, but predominantly on tasks that involve rational thinking (such as estimating a number). Here we tested this effect in the context of drawing geometrical shapes, which still enacts cognitive processes but mainly involves visuomotor control. We asked more than 700 school students to trace five patterns shown on a touchscreen and then aggregated their individual trajectories to improve the match with the original pattern. Our results show the characteristics of the strongest examples of Wisdom of the Crowd. First, the aggregate trajectory can be up to 5 times more accurate than the individual ones. Second, this great improvement requires aggregating trajectories from different individuals (rather than trials from the same individual). Third, the aggregate trajectory outperforms more than 99% of individual trajectories. Fourth, while older individuals outperform younger ones, a crowd of young individuals outperforms the average older one. These results demonstrate for the first time Wisdom of the Crowd in the realm of motor control, opening the door to further studies of human and also animal behavioural trajectories and their mechanistic underpinnings.

Impact of whole-cell bacterial immunoprophylaxis in the management of recurrent urinary tract infections in the frail elderly.

PURPOSE: This study aimed to determine the effectiveness of whole-cell bacterial immunotherapy, i.e. MV140 and autovaccines, in reducing the number ofurinary tract infections (UTIs)in frail elderly patients with recurrent UTI (RUTI). METHOD: A prospective cohort observational study was performed including 200 frail elderly subjects suffering RUTI, both females and males, between 2016 and 2018. The effectiveness of autovaccines and the polybacterial formulation MV140 (Uromune®), consisting ofwhole-cell heat-inactivated Escherichia coli25%, Klebsiella pneumoniae25%, Proteus vulgaris25% andEnterococcus faecalis25% were evaluated. Subjects initiated a 3-month sublingually daily course with MV140 or autovaccine, either first treatment or a new course if they had been previously vaccinated prior to inclusion in the study. Number of UTIs and quality of life (QoL, SF-36 score) were measured in the different study groups. RESULTS: The mean age for participants was 82.67 (SD, 7.12) for female and 80.23 (SD, 11.12) for male subjects. In all groups, 12 months following bacterial immunotherapy, the number of UTIs significantly decreased compared to before the treatment with autovaccine or MV140: the rate of reduction ranged between 7- and 40-fold. An increase in QoL scoring was also observed in any study group. When comparing medical interventions, MV140 conferred significantly higher benefit than autovaccines. For previously vaccinated individuals, a new 3-month course with MV140 or autovaccines provided further clinical improvement. CONCLUSIONS: MV140 and autovaccines emerge as valuable immunoprophylaxis for the management of RUTI in the frail elderly, contributing to an improvement in patient's quality of life. Herein, MV140 has shown to confer a higher effectiveness compared to autovaccines, regardless sex or course of treatment.

Inversion of pheromone preference optimizes foraging in C. elegans.

Foraging animals have to locate food sources that are usually patchily distributed and subject to competition. Deciding when to leave a food patch is challenging and requires the animal to integrate information about food availability with cues signaling the presence of other individuals (e.g., pheromones). To study how social information transmitted via pheromones can aid foraging decisions, we investigated the behavioral responses of the model animal Caenorhabditis elegans to food depletion and pheromone accumulation in food patches. We experimentally show that animals consuming a food patch leave it at different times and that the leaving time affects the animal preference for its pheromones. In particular, worms leaving early are attracted to their pheromones, while worms leaving later are repelled by them. We further demonstrate that the inversion from attraction to repulsion depends on associative learning and, by implementing a simple model, we highlight that it is an adaptive solution to optimize food intake during foraging.

Deciduous and evergreen oaks show contrasting adaptive responses in leaf mass per area across environments.

Increases in leaf mass per area (LMA) are commonly observed in response to environmental stresses and are achieved through increases in leaf thickness and/or leaf density. Here, we investigated how the two underlying components of LMA differ in relation to species native climates and phylogeny, across deciduous and evergreen species. Using a phylogenetic approach, we quantified anatomical, compositional and climatic variables from 40 deciduous and 45 evergreen Quercus species from across the Northern Hemisphere growing in a common garden. Deciduous species from shorter growing seasons tended to have leaves with lower LMA and leaf thickness than those from longer growing seasons, while the opposite pattern was found for evergreens. For both habits, LMA and thickness increased in arid environments. However, this shift was associated with increased leaf density in evergreens but reduced density in deciduous species. Deciduous and evergreen oaks showed fundamental leaf morphological differences that revealed a diverse adaptive response. While LMA in deciduous species may have diversified in tight coordination with thickness mainly modulated by aridity, diversification of LMA within evergreens appears to be dependent on the infrageneric group, with diversification in leaf thickness modulated by both aridity and cold, while diversification in leaf density is only modulated by aridity.

Clinical relevance of marginal factors on ultrafiltration in peritoneal dialysis.

BACKGROUND: Ultrafiltration (UF) in peritoneal dialysis (PD) is mainly driven by the osmotic gradient and peritoneal permeability, but other factors-such as intraperitoneal pressure (IPP)-also have an influence. METHODS: To assess the clinical relevance of these marginal factors, we studied 41 unselected PD patients undergoing two consecutive 2 h, 2.27% glucose exchanges, first with 2.5 L and then with 1.5 L. RESULTS: IPP, higher in the 2.5 L exchange, had a wide interpatient range, was higher in obese and polycystic patients and their increase with infusion volume was higher for women regardless of body size. UF with 2.5 L correlated inversely with IPP and was higher for patients with polycystosis or hernias, while for 1.5 L we found no significant correlations. The effluent had higher glucose and osmolarity in the 2.5 L exchange than in the 1.5 L one, similar for both sexes. In spite of this stronger osmotic gradient, only 21 patients had more UF in the 2.5 L exchange, with differences up to 240 mL. The other 20 patients had more UF in the 1.5 L exchange, with stronger differences (up to 800 mL, and more than 240 mL for 9 patients). The second group, with similar effluent osmolarity and peritoneal equilibration test (PET) parameters than the first, has higher IPP and preponderance of men. The sex influence is so intense that men decreased average UF with 2.5 L with respect to 1.5 L, while women increased it. CONCLUSIONS: With 2.27% glucose, sex and IPP-modulated by obesity, polycystosis, hernias, and intraperitoneal volume-significantly affect UF in clinical settings and might be useful for its management.

Intraperitoneal pressure: Stability over time and validation of Durand's measurement method.

Intraperitoneal pressure (IPP) is gaining consideration as a relevant parameter of peritoneal dialysis (PD) in adults, although many of its aspects are still pending clarification. We address here its stability over time and the validity of the usual method of clinical measurement, as proposed by Durand in 1992 but never specifically validated. We performed this validation by comparing Durand's method and direct measurements with a central venous pressure system. We performed a total of 250 measurement pairs in 50 patients with different intraperitoneal volumes plus in-vitro measurements with a simulated peritoneum. Absolute differences between the two systems in vivo were 0.87 ± 0.91 cmH2O (range 0-5 cmH2O); only 6.4% of them were ≥3 cmH2O. In vitro results for both methods were identical. We also compared IPP measurements in the same patient separated by 1-4 h (514 measurement pairs in 136 patients), 1 week (92 pairs in 92 patients), and 2 years (34 pairs in 17 patients). Net differences of measurements separated by hours or 1 week were close to 0 cmH2O, with oscillations of 1.5 cmH2O in hours and 2.3 cmH2O in 1 week. IPP measured 2 years apart presented a net decrease of 2.5 ± 4.9 cmH2O, without correlation with body mass index changes or any other usual parameter of PD. In hours, 7% of IPP differences were >3 cmH2O, 22% in 1 week, and 50% in 2 years. In conclusion, Durand's method is precise enough to measure IPP in peritoneal dialysis. This parameter is not stable over long timescales, so it is necessary to use recent measurements.

Immobilization in Ionogel: A New Way to Improve the Activity and Stability of Candida antarctica Lipase B.

New Candida antarctica lipase B derivatives with higher activity than the free enzyme were obtained by occlusion in an organogel of an ionic liquid (ionogel) based on the ionic liquid [Omim][PF6] and polyvinyl chloride. The inclusion of glutaraldehyde as a crosslinker improved the properties of the ionogel, allowing the enzymatic derivative to reach 5-fold higher activity than the free enzyme and also allowing it to be reused at 70 °C. The new methodology allows enzymatic derivatives to be designed by changing the ionic liquid, thus providing a suitable microenvironment for the enzyme. The ionic liquid may act on substrates to increase their local concentration, while reducing water activity in the enzyme's microenvironment. All this allows the activity and selectivity of the enzyme to be improved and greener processes to be developed. The chemical composition and morphology of the ionogel were also studied by scanning electron microscopy-energy dispersive X-ray spectroscopy, finding that porosity, which was related with the chemical composition, was a key factor for the enzyme activity.

Foliar plasticity related to gradients of heat and drought stress across crown orientations in three Mediterranean Quercus species.

Studies on plasticity at the level of a single individual plant provide indispensable information to predict leaf responses to climate change, because they allow better identification of the environmental factors that determine differences in leaf traits in the absence of genetic differences. Most of these studies have focused on the responses of leaf traits to variations in the light environment along vertical gradients, thus paying less attention to possible differences in the intensity of water stress among canopy orientations. In this paper, we analyzed the differences in leaf traits traditionally associated with changes in the intensity of water stress between east and west crown orientations in three Quercus species. The leaves facing west experienced similar solar radiation levels but higher maximum temperatures and lower daily minimum water potentials than those of the east orientation. In response to these differences, the leaves of the west orientation showed smaller size and less chlorophyll concentration, higher percentage of palisade tissue and higher density of stomata and trichomes. These responses would confirm the role of such traits in the tolerance to water stress and control of water losses by transpiration. For all traits, the species with the longest leaf life span exhibited the greatest plasticity between orientations. By contrast, no differences between canopy positions were observed for leaf thickness, leaf mass per unit area and venation patterns.

Asymmetric migration decreases stability but increases resilience in a heterogeneous metapopulation.

Many natural populations are spatially distributed, forming a network of subpopulations linked by migration. Migration patterns are often asymmetric and heterogeneous, with important consequences on the ecology and evolution of the species. Here we investigate experimentally how asymmetric migration and heterogeneous structure affect a simple metapopulation of budding yeast, formed by one strain that produces a public good and a non-producer strain that benefits from it. We study metapopulations with star topology and asymmetric migration, finding that all their subpopulations have a higher fraction of producers than isolated populations. Furthermore, the metapopulations have lower tolerance to challenging environments but higher resilience to transient perturbations. This apparent paradox occurs because tolerance to a constant challenge depends on the weakest subpopulations of the network, while resilience to a transient perturbation depends on the strongest ones.

Histone H4 acetylation regulates behavioral inter-individual variability in zebrafish.

BACKGROUND: Animals can show very different behaviors even in isogenic populations, but the underlying mechanisms to generate this variability remain elusive. We use the zebrafish (Danio rerio) as a model to test the influence of histone modifications on behavior. RESULTS: We find that laboratory and isogenic zebrafish larvae show consistent individual behaviors when swimming freely in identical wells or in reaction to stimuli. This behavioral inter-individual variability is reduced when we impair the histone deacetylation pathway. Individuals with high levels of histone H4 acetylation, and specifically H4K12, behave similarly to the average of the population, but those with low levels deviate from it. More precisely, we find a set of genomic regions whose histone H4 acetylation is reduced with the distance between the individual and the average population behavior. We find evidence that this modulation depends on a complex of Yin-yang 1 (YY1) and histone deacetylase 1 (HDAC1) that binds to and deacetylates these regions. These changes are not only maintained at the transcriptional level but also amplified, as most target regions are located near genes encoding transcription factors. CONCLUSIONS: We suggest that stochasticity in the histone deacetylation pathway participates in the generation of genetic-independent behavioral inter-individual variability.

Disentangling and modeling interactions in fish with burst-and-coast swimming reveal distinct alignment and attraction behaviors.

The development of tracking methods for automatically quantifying individual behavior and social interactions in animal groups has open up new perspectives for building quantitative and predictive models of collective behavior. In this work, we combine extensive data analyses with a modeling approach to measure, disentangle, and reconstruct the actual functional form of interactions involved in the coordination of swimming in Rummy-nose tetra (Hemigrammus rhodostomus). This species of fish performs burst-and-coast swimming behavior that consists of sudden heading changes combined with brief accelerations followed by quasi-passive, straight decelerations. We quantify the spontaneous stochastic behavior of a fish and the interactions that govern wall avoidance and the reaction to a neighboring fish, the latter by exploiting general symmetry constraints for the interactions. In contrast with previous experimental works, we find that both attraction and alignment behaviors control the reaction of fish to a neighbor. We then exploit these results to build a model of spontaneous burst-and-coast swimming and interactions of fish, with all parameters being estimated or directly measured from experiments. This model quantitatively reproduces the key features of the motion and spatial distributions observed in experiments with a single fish and with two fish. This demonstrates the power of our method that exploits large amounts of data for disentangling and fully characterizing the interactions that govern collective behaviors in animals groups.

Adversity magnifies the importance of social information in decision-making.

Decision-making theories explain animal behaviour, including human behaviour, as a response to estimations about the environment. In the case of collective behaviour, they have given quantitative predictions of how animals follow the majority option. However, they have so far failed to explain that in some species and contexts social cohesion increases when conditions become more adverse (i.e. individuals choose the majority option with higher probability when the estimated quality of all available options decreases). We have found that this failure is due to modelling simplifications that aided analysis, like low levels of stochasticity or the assumption that only one choice is the correct one. We provide a more general but simple geometric framework to describe optimal or suboptimal decisions in collectives that gives insight into three different mechanisms behind this effect. The three mechanisms have in common that the private information acts as a gain factor to social information: a decrease in the privately estimated quality of all available options increases the impact of social information, even when social information itself remains unchanged. This increase in the importance of social information makes it more likely that agents will follow the majority option. We show that these results quantitatively explain collective behaviour in fish and experiments of social influence in humans.

Preferential interactions promote blind cooperation and informed defection.

It is common sense that costs and benefits should be carefully weighed before deciding on a course of action. However, we often disapprove of people who do so, even when their actual decision benefits us. For example, we prefer people who directly agree to do us a favor over those who agree only after securing enough information to ensure that the favor will not be too costly. Why should we care about how people make their decisions, rather than just focus on the decisions themselves? Current models show that punishment of information gathering can be beneficial because it forces blind decisions, which under some circumstances enhances cooperation. Here we show that aversion to information gathering can be beneficial even in the absence of punishment, due to a different mechanism: preferential interactions with reliable partners. In a diverse population where different people have different-and unknown-preferences, those who seek additional information before agreeing to cooperate reveal that their preferences are close to the point where they would choose not to cooperate. Blind cooperators are therefore more likely to keep cooperating even if conditions change, and aversion to information gathering helps to interact preferentially with them. Conversely, blind defectors are more likely to keep defecting in the future, leading to a preference for informed defectors over blind ones. Both mechanisms-punishment to force blind decisions and preferential interactions-give qualitatively different predictions, which may enable experimental tests to disentangle them in real-world situations.

A New Method to Increase Ultrafiltration in Peritoneal Dialysis: Steady Concentration Peritoneal Dialysis.

UNLABELLED: ♦ BACKGROUND: Peritoneal dialysis (PD) has limited power for liquid extraction (ultrafiltration), so fluid overload remains a major cause of treatment failure. ♦ METHODS: We present steady concentration peritonal dialysis (SCPD), which increases ultrafiltration of PD exchanges by maintaining a constant peritoneal glucose concentration. This is achieved by infusing 50% glucose solution at a constant rate (typically 40 mL/h) during the 4-hour dwell of a 2-L 1.36% glucose exchange. We treated 21 fluid overload episodes on 6 PD patients with high or average-high peritoneal transport characteristics who refused hemodialysis as an alternative. Each treatment consisted of a single session with 1 to 4 SCPD exchanges (as needed). ♦ RESULTS: Ultrafiltration averaged 653 ± 363 mL/4 h - twice the ultrafiltration of the peritoneal equilibration test (PET) (300 ± 251 mL/4 h, p < 0.001) and 6-fold the daily ultrafiltration (100 ± 123 mL/4 h, p < 0.001). Serum and peritoneal glucose stability and dialysis efficacy were excellent (glycemia 126 ± 25 mg/dL, peritoneal glucose 1,830 ± 365 mg/dL, D/P creatinine 0.77 ± 0.08). The treatment reversed all episodes of fluid overload, avoiding transfer to hemodialysis. Ultrafiltration was proportional to fluid overload (p < 0.01) and inversely proportional to final peritoneal glucose concentration (p < 0.05). ♦ CONCLUSION: This preliminary clinical experience confirms the potential of SCPD to safely and effectively increase ultrafiltration of PD exchanges. It also shows peritoneal transport in a new dynamic context, enhancing the influence of factors unrelated to the osmotic gradient.