Increased performance of Cirsium arvense from the invasive range

The Evolution of Increased Competitive Ability (EICA) hypothesis suggests that plants from the invasive range should perform better than plants of the same species from the native range. To properly test this, we need to compare growth of plants from the two ranges in a common environment. Ideally, all the natural enemies should be excluded, to make sure that the differences are not due to different response of plants from the two ranges to the natural enemies. We used the above design to examine the difference in growth and reproduction in Cirsium arvense plants from the invasive (North America) and native range (Europe). To account for possible differences within the ranges, we used plants from two regions, separated by at least 1000 km, in each range. Because the higher performance of species from the invasive range can be caused by their higher ability to acquire resources we compared growth of the plants in two different nutrient levels. The results indicate that plants from the invasive range are larger in most size parameters as well as parameters more closely related to fitness. For aboveground biomass, the response of plants from the invasive range to nutrient addition was weaker than that of plants from the native range and the difference between the ranges was stronger in the nutrient poor substrate. The results are in agreement with the EICA hypothesis and suggest that plants from the invasive range have higher ability to use resources and are thus able to perform well also in nutrient poor conditions.     

You are what your mother eats: evidence for maternal preconception diet influencing foetal sex in humans

Facultative adjustment of sex ratios by mothers occurs in some animals, and has been linked to resource availability. In mammals, the search for consistent patterns is complicated by variations in mating systems, social hierarchies and litter sizes. Humans have low fecundity, high maternal investment and a potentially high differential between the numbers of offspring produced by sons and daughters: these conditions should favour the evolution of facultative sex ratio variation. Yet little is known of natural mechanisms of sex allocation in humans. Here, using data from 740 British women who were unaware of their foetus's gender, we show that foetal sex is associated with maternal diet at conception. Fifty six per cent of women in the highest third of preconceptional energy intake bore boys, compared with 45% in the lowest third. Intakes during pregnancy were not associated with sex, suggesting that the foetus does not manipulate maternal diet. Our results support hypotheses predicting investment in costly male offspring when resources are plentiful. Dietary changes may therefore explain the falling proportion of male births in industrialized countries. The results are relevant to the current debate about the artificial selection of offspring sex in fertility treatment and commercial 'gender clinics'.     

Distance-dependence in two Amazonian palms: effects of spatial and temporal variation in seed predator communities

Animals aid population growth and fitness in tropical forest communities through dispersal and negatively impact populations through seed predation. The interaction between dispersal and seed predation can produce distance- or density-dependence; powerful mechanisms for maintaining species diversity incorporated in the Janzen–Connell model. Large mammals, the highest biomass seed predators of intact Amazonian communities and at risk due to human disturbance, are potentially central to these interactions. This study tests the Janzen–Connell model and investigates the impact of mammalian seed predators on seedling recruitment and maintenance of tree diversity. Patterns of both vertebrate and invertebrate seed predation and seedling recruitment were studied in the two most abundant canopy tree species in western Amazonia (Arecaceae: Astrocaryum murumuru and Iriartea deltoidea). We specifically examined effects of both spatial and temporal variation of the highest biomass seed predator in southwest Amazonian forests, the white-lipped peccary (Tayassu pecari), on recruitment through disturbed and undisturbed sites and through a fortuitous 12 year natural extinction and recolonization event of T. pecari. Distance-dependent seedling recruitment was found in Astrocaryum and Iriartea at both sites. However, the median distance of seedlings was ~1.5× farther from reproductive adults in both palms at the undisturbed site. The number of Iriartea seeds escaping predation increased 6,000% in both space and time due to the decline of T. pecari abundance. The results demonstrate that Janzen–Connell effects are stronger in intact ecosystems and tie these mechanistically to changes in seed predator abundance. This study shows that anthropogenic changes in mammal communities decrease the magnitude of Janzen–Connell effects in Amazonian forests and may result in decreases in tree diversity.     

Markov modelling of immunological and virological states in HIV-1 infected patients

The purpose of this study was to evaluate the evolution of HIV infected patients and to bring out some significant factors associated with this pathology. The main criteria revealing the State of illness is viral load measurement (VL). However the CD4 lymphocytes also represent an important marker as these reflect the State of the immune reservoir. Many studies have been carried out in this field and different models have been proposed with a view to a better understanding of this disease. Multi State Markov models defined in terms of CD4 counts, or in terms of viral load, have proved to be very useful tools for modelling HIV disease progression. The model we have developed in this study is based on both the CD4 lymphocytes counts and VL. Markov models are characterized by transition intensities. In this paper we explored several structures in succession. First, we used a homogeneous continuous time Markov process with four states defined by crossed values of CD4 and VL in a given patient at a given time. Then, the effect of certain covariates on the infection process was introduced into the model via the transition intensity functions, as with a Cox regression model. Since the hypothesis of homogeneity may be unrealistic in certain cases, we also considered piecewise homogeneous Markov models. Finally, the effects of covariates and time were combined in a piecewise homogeneous model with a covariate. We applied these methods to data from 1313 HIV-infected patients included in the NADIS cohort.     

Conformational change of syntaxin linker region induced by Munc13s initiates SNARE complex formation in synaptic exocytosis

The soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) protein syntaxin-1 adopts a closed conformation when bound to Munc18-1, preventing binding to synaptobrevin-2 and SNAP-25 to form the ternary SNARE complex. Although it is known that the MUN domain of Munc13-1 catalyzes the transition from the Munc18-1/syntaxin-1 complex to the SNARE complex, the molecular mechanism is unclear. Here, we identified two conserved residues (R151, I155) in the syntaxin-1 linker region as key sites for the MUN domain interaction. This interaction is essential for SNARE complex formation in vitro and synaptic vesicle priming in neuronal cultures. Moreover, this interaction is important for a tripartite Munc18-1/syntaxin-1/MUN complex, in which syntaxin-1 still adopts a closed conformation tightly bound to Munc18-1, whereas the syntaxin-1 linker region changes its conformation, similar to that of the LE mutant of syntaxin-1 when bound to Munc18-1. We suggest that the conformational change of the syntaxin-1 linker region induced by Munc13-1 initiates ternary SNARE complex formation in the neuronal system.     

Parasites and showy males: malarial infection and color variation in fence lizards

Summary Hamilton and Zuk (1982) proposed that the quality of male showy traits reflects genetically-based resistance to parasites and can be used by females to select mates that are less prone to parasitic attack. The hypothesis requires that a particular state of a variable showy trait should be associated with parasite infection. We tested this idea with a population of western fence lizards, Sceloporus occidentalis, infected with the malarial parasite, Plasmodium mexicanum. Ventral color pattern is strongly dimorphic in fence lizards and varies greatly among males in this population. Malaria-infected males exhibited significantly more black and less pale on their ventral surface than did noninfected males of similar body size. This difference was not a function of differing ages of infected and noninfected animals of the same body size. However, logistic regression demonstrated that females using male ventral color as a gauge of infection status would only marginally improve their chance of choosing a noninfected lizard over random selection of mates.     

Production of Ethanol from Maltose by Zymobacter palmae Fermentation

The production of ethanol from maltose by Zymobacter palmae T109 in monoculture fermentations, and in co-culture fermentations together with Zymomonas mobilis B69 was studies. Zymobacter palmae T109, produced 5.5% (w/v) of ethanol when co-cultured with Zymomonas mobilis B69, but Zymobacter palmae T109 produced only 4.9% (w/v) ethanol from 15% (w/v) maltose medium in monoculture fermentation.     

Activity-dependent release of phosphorylated human tau from Drosophila neurons in primary culture

Neuronal activity can enhance tau release and thus accelerate tauopathies. This activity-dependent tau release can be used to study the progression of tau pathology in Alzheimer''s disease (AD), as hyperphosphorylated tau is implicated in AD pathogenesis and related tauopathies. However, our understanding of the mechanisms that regulate activity-dependent tau release from neurons and the role that tau phosphorylation plays in modulating activity-dependent tau release is still rudimentary. In this study, Drosophila neurons in primary culture expressing human tau (hTau) were used to study activity-dependent tau release. We found that hTau release was markedly increased by 50 mM KCl treatment for 1 h. A similar level of release was observed using optogenetic techniques, where genetically targeted neurons were stimulated for 30 min using blue light (470 nm). Our results showed that activity-dependent release of phosphoresistant hTau^S11A was reduced when compared with wildtype hTau. In contrast, release of phosphomimetic hTau^E14 was increased upon activation. We found that released hTau was phosphorylated in its proline-rich and C-terminal domains using phosphorylation site-specific tau antibodies (e.g., AT8). Fold changes in detectable levels of total or phosphorylated hTau in cell lysates or following immunopurification from conditioned media were consistent with preferential release of phosphorylated hTau after light stimulation. This study establishes an excellent model to investigate the mechanism of activity-dependent hTau release and to better understand the role of phosphorylated tau release in the pathogenesis of AD since it relates to alterations in the early stage of neurodegeneration associated with increased neuronal activity.     

Genetic sex determination,sex chromosome size and sex-specific lifespans across tetrapods

Sex differences in lifespan are ubiquitous across the tree of life and exhibit broad taxonomic patterns that remain a puzzle, such as males living longer than females in birds and vice versa in mammals. The prevailing unguarded X hypothesis explains sex differences in lifespan by differential expression of recessive mutations on the X or Z chromosome of the heterogametic sex, but has only received indirect support to date. An alternative hypothesis is that the accumulation of deleterious mutations and repetitive elements on the Y or W chromosome might lower the survival of the heterogametic sex (‘toxic Y’ hypothesis). Here, we use a new database to report lower survival of the heterogametic relative to the homogametic sex across 136 species of birds, mammals, reptiles and amphibians, as expected if sex chromosomes shape sex-specific lifespans, and consistent with previous findings. We also found that the relative sizes of both the X and the Y chromosomes in mammals (but not the Z or the W chromosomes in birds) are associated with sex differences in lifespan, as predicted by the unguarded X and the ‘toxic Y’. Furthermore, we report that the relative size of the Y is negatively associated with male lifespan in mammals, so that small Y size correlates with increased male lifespan. In theory, toxic Y effects are expected to be particularly strong in mammals, and we did not find similar effects in birds. Our results confirm the role of sex chromosomes in explaining sex differences in lifespan across tetrapods and further suggest that, at least in mammals, ‘toxic Y’ effects may play an important part in this role.