Wheat germ agglutinin treatment of follicle cell-free mouse oocytes inhibits fertilization

Controversy exists whether treatment of follicle cell-free oocytes with wheat germ agglutinin (WGA) prevents fertilization. Lack of inhibition in one case has led to the suggestion that acrosin may not be a zona lysin. To re-examine the effect of the WGA, the zona pellucida of follicle cell-free mouse oocytes was made more resistant to proteinase digestion by treatment with 10 or 50 μg/ml WGA. Such WGA-treated oocytes showed decreased fertilizability when washed to remove excess WGA and incubated with capacitated spermatozoa. Oocyte cleavage was used as an end point, because a large number of spermatozoa adhered to the eggs after WGA treatment, making observation of sperm penetration and pronucleus formation unreliable. Resistance to proteinase digestion increased, and the fertilizability decreased with the higher amount of WGA. The action of WGA was most likely not mediated by a direct effect on sperm motility, sperm acrosin activity, sperm binding to the zona pellucida, or oocyte cleavage. WGA did not affect the acrosome reaction of guinea pig spermatozoa. These data show that WGA treatment of follicle cell-free mouse oocytes results in decreased fertilizability, possibly by rendering the zona pellucida more resistant to sperm proteinase digestion.     

Effect of malaria in pregnancy on foetal cortical brain development: a longitudinal observational study

ABSTRACT: BACKGROUND: Malaria in pregnancy has a negative impact on foetal growth, but it is not known whether this also affects the foetal nervous system. The aim of this study was to examine the effects of malaria on foetal cortex development by three-dimensional ultrasound. METHODS: Brain images were acquired using a portable ultrasound machine and a 3D ultrasound transducer. All recordings were analysed, blinded to clinical data, using the 4D view software package. The foetal supra-tentorial brain volume was determined and cortical development was qualitatively followed by scoring the appearance and development of six sulci. Multilevel analysis was used to study brain volume and cortical development in individual foetuses, RESULTS: Cortical grading was possible in 161 out of 223 (72%) serial foetal brain images in pregnant women living in a malaria endemic area. There was no difference between foetal cortical development or brain volumes at any time in pregnancy between women with immediately treated malaria infections and non-infected pregnancies. CONCLUSION: The percentage of images that could be graded was similar to other neuro-sonographic studies. Maternal malaria does not have a gross effect on foetal brain development, at least in this population, which had access to early detection and effective treatment of malaria.     

Relative growth rate variation of evergreen and deciduous savanna tree species is driven by different traits

Background and Aims

Plant relative growth rate (RGR) depends on biomass allocation to leaves (leaf mass fraction, LMF), efficient construction of leaf surface area (specific leaf area, SLA) and biomass growth per unit leaf area (net assimilation rate, NAR). Functional groups of species may differ in any of these traits, potentially resulting in (1) differences in mean RGR of groups, and (2) differences in the traits driving RGR variation within each group. We tested these predictions by comparing deciduous and evergreen savanna trees.

Methods

RGR, changes to biomass allocation and leaf morphology, and root non-structural carbohydrate reserves were evaluated for juveniles of 51 savanna species (34 deciduous, 17 evergreen) grown in a common garden experiment. It was anticipated that drivers of RGR would differ between leaf habit groups because deciduous species have to allocate carbohydrates to storage in roots to be able to flush leaves again, which directly compromises their LMF, whereas evergreen species are not subject to this constraint.

Key Results

Evergreen species had greater LMF and RGR than deciduous species. Among deciduous species LMF explained 27 % of RGR variation (SLA 34 % and NAR 29 %), whereas among evergreen species LMF explained between 2 and 17 % of RGR variation (SLA 32–35 % and NAR 38–62 %). RGR and LMF were (negatively) related to carbohydrate storage only among deciduous species.

Conclusions

Trade-offs between investment in carbohydrate reserves and growth occurred only among deciduous species, leading to differences in relative contribution made by the underlying components of RGR between the leaf habit groups. The results suggest that differences in drivers of RGR occur among savanna species because these have different selected strategies for coping with fire disturbance in savannas. It is expected that variation in the drivers of RGR will be found in other functional types that respond differently to particular disturbances.     

Effects of ENSO and Temporal Rainfall Variation on the Dynamics of Successional Communities in Old-Field Succession of a Tropical Dry Forest

The effects of temporal variation of rainfall on secondary succession of tropical dry ecosystems are poorly understood. We studied effects of inter-seasonal and inter-year rainfall variation on the dynamics of regenerative successional communities of a tropical dry forest in Mexico. We emphasized the effects caused by the severe El Niño Southern Oscillation (ENSO) occurred in 2005. We established permanent plots in sites representing a chronosequence of Pasture (abandoned pastures, 0–1 years fallow age), Early (3–5), Intermediate (8–12), and Old-Growth Forest categories (n = 3 per category). In total, 8210 shrubs and trees 10 to 100-cm height were identified, measured, and monitored over four years. Rates of plant recruitment, growth and mortality, and gain and loss of species were quantified per season (dry vs. rainy), year, and successional category, considering whole communities and separating seedlings from sprouts and shrubs from trees. Community rates changed with rainfall variation without almost any effect of successional stage. Mortality and species loss rates peaked during the ENSO year and the following year; however, after two rainy years mortality peaked in the rainy season. Such changes could result from the severe drought in the ENSO year, and of the outbreak of biotic agents during the following rainy years. Growth, recruitment and species gain rates were higher in the rainy season but they were significantly reduced after the ENSO year. Seedlings exhibited higher recruitment and mortality rate than sprouts, and shrubs showed higher recruitment than trees. ENSO strongly impacted both the dynamics and trajectory of succession, creating transient fluctuations in the abundance and species richness of the communities. Overall, there was a net decline in plant and species density in most successional stages along the years. Therefore, strong drought events have critical consequences for regeneration dynamics, delaying the successional process and modifying the resilience of these systems.     

Are lianas more drought-tolerant than trees? A test for the role of hydraulic architecture and other stem and leaf traits

Lianas are an important component of Neotropical forests, where evidence suggests that they are increasing in abundance and biomass. Lianas are especially abundant in seasonally dry tropical forests, and as such it has been hypothesized that they are better adapted to drought, or that they are at an advantage under the higher light conditions in these forests. However, the physiological and morphological characteristics that allow lianas to capitalize more on seasonal forest conditions compared to trees are poorly understood. Here, we evaluate how saplings of 21 tree and liana species from a seasonal tropical forest in Panama differ in cavitation resistance (P ₅₀) and maximum hydraulic conductivity (K _h), and how saplings of 24 tree and liana species differ in four photosynthetic leaf traits (e.g., maximum assimilation and stomatal conductance) and six morphological leaf and stem traits (e.g., wood density, maximum vessel length, and specific leaf area). At the sapling stage, lianas had a lower cavitation resistance than trees, implying lower drought tolerance, and they tended to have a higher potential hydraulic conductivity. In contrast to studies focusing on adult trees and lianas, we found no clear differences in morphological and photosynthetic traits between the life forms. Possibly, lianas and trees are functionally different at later ontogenetic stages, with lianas having deeper root systems than trees, or experience their main growth advantage during wet periods, when they are less vulnerable to cavitation and can achieve high conductivity. This study shows, however, that the hydraulic characteristics and functional traits that we examined do not explain differences in liana and tree distributions in seasonal forests.     

Hydraulics and life history of tropical dry forest tree species: coordination of species' drought and shade tolerance

Plant hydraulic architecture has been studied extensively, yet we know little about how hydraulic properties relate to species' life history strategies, such as drought and shade tolerance. The prevailing theories seem contradictory. We measured the sapwood (K(s) ) and leaf (K(l) ) hydraulic conductivities of 40 coexisting tree species in a Bolivian dry forest, and examined associations with functional stem and leaf traits and indices of species' drought (dry-season leaf water potential) and shade (juvenile crown exposure) tolerance. Hydraulic properties varied across species and between life-history groups (pioneers vs shade-tolerant, and deciduous vs evergreen species). In addition to the expected negative correlation of K(l) with drought tolerance, we found a strong, negative correlation between K(l) and species' shade tolerance. Across species, K(s) and K(l) were negatively correlated with wood density and positively with maximum vessel length. Consequently, drought and shade tolerance scaled similarly with hydraulic properties, wood density and leaf dry matter content. We found that deciduous species also had traits conferring efficient water transport relative to evergreen species. Hydraulic properties varied across species, corresponding to the classical trade-off between hydraulic efficiency and safety, which for these dry forest trees resulted in coordinated drought and shade tolerance across species rather than the frequently hypothesized trade-off.     

The small world of psychopathology

Background

Mental disorders are highly comorbid: people having one disorder are likely to have another as well. We explain empirical comorbidity patterns based on a network model of psychiatric symptoms, derived from an analysis of symptom overlap in the Diagnostic and Statistical Manual of Mental Disorders-IV (DSM-IV).

Principal Findings

We show that a) half of the symptoms in the DSM-IV network are connected, b) the architecture of these connections conforms to a small world structure, featuring a high degree of clustering but a short average path length, and c) distances between disorders in this structure predict empirical comorbidity rates. Network simulations of Major Depressive Episode and Generalized Anxiety Disorder show that the model faithfully reproduces empirical population statistics for these disorders.

Conclusions

In the network model, mental disorders are inherently complex. This explains the limited successes of genetic, neuroscientific, and etiological approaches to unravel their causes. We outline a psychosystems approach to investigate the structure and dynamics of mental disorders.     

Architecture of Iberian canopy tree species in relation to wood density,shade tolerance and climate

Tree architecture has important consequences for tree performance as it determines resource capture, mechanical stability and dominance over competitors. We analyzed architectural relationships between stem and crown dimensions for 13 dominant Iberian canopy tree species belonging to the Pinaceae (six Pinus species) and Fagaceae (six Quercus species and Fagus sylvatica) and related these architectural traits to wood density, shade tolerance and climatic factors. Fagaceae had, compared with Pinaceae, denser wood, saplings with wider crowns and adults with larger maximal crown size but smaller maximal height. In combination, these traits enhance light acquisition and persistence in shaded environments; thus, contributing to their shade tolerance. Pinaceae species, in contrast, had low-density wood, allocate more resources to the formation of the central trunk rather than to branches and attained taller maximal heights, allowing them to grow rapidly in height and compete for light following disturbances; thus, contributing to their high light requirements. Wood density had a strong relationship with tree architecture, with dense-wooded species having smaller maximum height and wider crowns, probably because of cheaper expansion costs for producing biomechanically stable branches. Species from arid environments had shorter stems and shallower crowns for a given stem diameter, probably to reduce hydraulic path length and assure water transport. Wood density is an important correlate of variation in tree architecture between species and the two dominant families, with potentially large implications for their resource foraging strategies and successional dynamics.