Plant Community Diversity Influences Allocation to Direct Chemical Defence in Plantago lanceolata

Background: Forecasting the consequences of accelerating rates of changes in biodiversity for ecosystem functioning requires a mechanistic understanding of the relationships between the structure of biological communities and variation in plant functional characteristics. So far, experimental data of how plant species diversity influences the investment of individual plants in direct chemical defences against herbivores and pathogens is lacking. Methodology/Principal Findings: We used Plantago lanceolata as a model species in experimental grasslands differing in species richness and composition (Jena Experiment) to investigate foliar concentrations of the iridoid glycosides (IG), catalpol and its biosynthetic precursor aucubin. Total IG and aucubin concentrations decreased, while catalpol concentrations increased with increasing plant diversity in terms of species or functional group richness. Negative plant diversity effects on total IG and aucubin concentrations correlated with increasing specific leaf area of P. lanceolata, suggesting that greater allocation to light acquisition reduced the investment into these carbon-based defence components. In contrast, increasing leaf nitrogen concentrations best explained increasing concentrations of the biosynthetically more advanced IG, catalpol. Observed levels of leaf damage explained a significant proportion of variation in total IG and aucubin concentrations, but did not account for variance in catalpol concentrations. Conclusions/Significance: Our results clearly show that plants growing in communities of varying species richness an

Competitive Performance of Transgenic Wheat Resistant to Powdery Mildew

Genetically modified (GM) plants offer an ideal model system to study the influence of single genes that confer constitutive resistance to pathogens on the ecological behaviour of plants. We used phytometers to study competitive interactions between GM lines of spring wheat Triticum aestivum carrying such genes and control lines. We hypothesized that competitive performance of GM lines would be reduced due to enhanced transgene expression under pathogen levels typically encountered in the field. The transgenes pm3b from wheat (resistance against powdery mildew Blumeria graminis) or chitinase and glucanase genes from barley (resistance against fungi in general) were introduced with the ubiquitin promoter from maize (pm3b and chitinase genes) or the actin promoter from rice (glucanase gene). Phytometers of 15 transgenic and non-transgenic wheat lines were transplanted as seedlings into plots sown with the same 15 lines as competitive environments and subject to two soil nutrient levels. Pm3b lines had reduced mildew incidence compared with control lines. Chitinase and chitinase/glucanase lines showed the same high resistance to mildew as their control in low-nutrient treatment and slightly lower mildew rates than the control in high-nutrient environment. Pm3b lines were weaker competitors than control lines. This resulted in reduced yield and seed number. The Pm3b line with the highest transgene expression had 53.2% lower yield than the control whereas the Pm3b line which segregated in resistance and had higher mildew rates showed only minor costs under competition. The line expressing both chitinase and glucanase genes also showed reduced yield and seed number under competition compared with its control. Our results suggest that single transgenes conferring constitutive resistance to pathogens can have ecological costs and can weaken plant competitiveness even in the presence of the pathogen. The magnitude of these costs appears related to the degree of expression of the transgenes

Within-host evolution of Staphylococcus aureus during asymptomatic carriage

Background Staphylococcus aureus is a major cause of healthcare associated mortality, but like many important bacterial pathogens, it is a common constituent of the normal human body flora. Around a third of healthy adults are carriers. Recent evidence suggests that evolution of S. aureus during nasal carriage may be associated with progression to invasive disease. However, a more detailed understanding of within-host evolution under natural conditions is required to appreciate the evolutionary and mechanistic reasons why commensal bacteria such as S. aureus cause disease. Therefore we examined in detail the evolutionary dynamics of normal, asymptomatic carriage. Sequencing a total of 131 genomes across 13 singly colonized hosts using the Illumina platform, we investigated diversity, selection, population dynamics and transmission during the short-term evolution of S. aureus. Principal Findings We characterized the processes by which the raw material for evolution is generated: micro-mutation (point mutation and small insertions/deletions), macro-mutation (large insertions/deletions) and the loss or acquisition of mobile elements (plasmids and bacteriophages). Through an analysis of synonymous, non-synonymous and intergenic mutations we discovered a fitness landscape dominated by purifying selection, with rare examples of adaptive change in genes encoding surface-anchored proteins and an enterotoxin. We found evidence for dramatic, hundred-fold fluctuations in the size of the within-host population over time, which we related to the cycle of colonization and clearance. Using a newly-developed population genetics approach to detect recent transmission among hosts, we revealed evidence for recent transmission between some of our subjects, including a husband and wife both carrying populations of methicillin-resistant S. aureus (MRSA). Significance This investigation begins to paint a picture of the within-host evolution of an important bacterial pathogen during its prevailing natural state, asymptomatic carriage. These results also have wider significance as a benchmark for future systematic studies of evolution during invasive S. aureus disease

Correlates of health-related quality of life in primary caregivers of perinatally HIV infected and HIV exposed uninfected adolescents at the Kenyan Coast

Background Mothers and other primary caregivers play a crucial role in looking after perinatally HIV infected, and HIV exposed uninfected adolescents in sub-Saharan Africa. Day- to-day caregiving in the context of limited instrumental support and added biomedical risk (HIV seropositivity) may expose these caregivers to adverse states of health. Unfortunately, very few studies have examined their health-related quality of life (HRQoL). Our study documents the HRQoL profile, and associated factors in primary caregivers of perinatally HIV infected, perinatally HIV exposed but uninfected and HIV unexposed/uninfected adolescents aged 12–17 years at the Kenyan Coast. Methods This was a cross-sectional analysis of 485 primary caregivers: 195 of perinatally HIV infected adolescents, 128 of perinatally HIV exposed but uninfected adolescents and 162 of HIV unexposed/uninfected adolescents. All caregivers completed a self-report measure of HRQoL (having 8 subscales), depressive symptoms, and parenting stress. They also provided their sociodemographic information and that of the care recipients. We used one-way analysis of variance to assess statistical differences among the groups. Linear regression analyses were used to identify correlates of HRQoL. Results Overall, caregivers of HIV unexposed/uninfected adolescents reported significantly higher mean HRQoL scores than the other caregivers in the overall HRQoL domain and majority of the subscales. There were no statistical differences in the overall HRQoL scores and most subscales between caregivers of HIV exposed adolescents. Linear regression analyses across the sample indicated that depressive symptoms, increasing age of caregiver, and caring for an adolescent perinatally exposed to HIV were significantly associated with reduced HRQoL at both the overall and sub-scale level. Having a professional job relative to subsistence farming was the only factor associated with improved overall HRQoL. At subscale level, higher socioeconomic status correlated positively with HRQoL while being a grandparent, level of education, parenting stress were negatively associated with HRQoL. Conclusions Caregivers in this sample, especially those who are ageing, at risk of mental ill-health, and taking care of adolescents perinatally exposed to HIV, appear to be vulnerable to poor quality of life. Inclusive and multi-component interventions tailored to the caregivers' psychosocial and mental needs will potentially enhance their quality of life