Ecological implications of invasive tunicates associated with artificial structures in Puget Sound, Washington, USA

The non-native tunicates Didemnum vexillum, Ciona savignyi, and Styela clava are of concern to resource managers of Puget Sound, Washington, USA because they have been shown to threaten native species diversity and shellfish aquaculture in other regions. Invasive tunicates in Puget Sound occur mainly on man-made structures such as floating docks and aquaculture facilities. We conducted studies of the three species of concern and a fourth introduced tunicate, Botrylloides violaceus, that occur on these structures to evaluate their effects on mussels and native invertebrate communities. Because most studies of community effects of tunicates have dealt with sessile fouling organisms, we focused instead on epibenthic organisms such as meiofaunal harpacticoid copepods and macrofaunal polychaetes and amphipods that are known to be important prey for juvenile salmon and other small fish. Similar studies have shown mixed results, with negative, positive, or no effects depending on the species. We also found few community-level effects. Abundances of several species were lower when tunicates were present, but only at some of the sites. Several other species, including a non-native isopod, were significantly more abundant in the presence of tunicates. However, in most cases results were not statistically significant and more intensive, controlled sampling or experiments may be needed to demonstrate any consistent tunicate effects. Although invasive tunicates cause problems for mussel growers elsewhere, we did not find negative effects on mussels at four sites in Puget Sound. Given the large impacts known to accompany tunicate invasions elsewhere and their relatively recent invasions into Puget Sound, monitoring of their populations and effects should continue in the region.     

Human metabolic profiles are stably controlled by genetic and environmental variation

¹H Nuclear Magnetic Resonance spectroscopy (¹H NMR) is increasingly used to measure metabolite concentrations in sets of biological samples for top‐down systems biology and molecular epidemiology. For such purposes, knowledge of the sources of human variation in metabolite concentrations is valuable, but currently sparse. We conducted and analysed a study to create such a resource. In our unique design, identical and non‐identical twin pairs donated plasma and urine samples longitudinally. We acquired ¹H NMR spectra on the samples, and statistically decomposed variation in metabolite concentration into familial (genetic and common‐environmental), individual‐environmental, and longitudinally unstable components. We estimate that stable variation, comprising familial and individual‐environmental factors, accounts on average for 60% (plasma) and 47% (urine) of biological variation in ¹H NMR‐detectable metabolite concentrations. Clinically predictive metabolic variation is likely nested within this stable component, so our results have implications for the effective design of biomarker‐discovery studies. We provide a power‐calculation method which reveals that sample sizes of a few thousand should offer sufficient statistical precision to detect ¹H NMR‐based biomarkers quantifying predisposition to disease.     

Impact of non-HIV and HIV risk factors on survival in HIV-infected patients on HAART: a population-based nationwide cohort study

Background

We determined the impact of three factors on mortality in HIV-infected patients who had been on highly active antiretroviral therapy (HAART) for at least one year: (1) insufficient response to (HAART) and presence of AIDS-defining diseases, (2) comorbidity, and (3) drug and alcohol abuse and compared the mortality to that of the general population.

Methodology/Principal Findings

In a Danish nationwide, population-based cohort study, we used population based registries to identify (1) all Danish HIV-infected patients who started HAART in the period 1 January 1998–1 July 2009, and (2) a comparison cohort of individuals matched on date of birth and gender (N = 2,267 and 9,068, respectively). Study inclusion began 1 year after start of HAART. Patients were categorised hierarchically in four groups according to the three risk factors, which were identified before study inclusion. The main outcome measure was probability of survival from age 25 to 65 years. The probability of survival from age 25 to age 65 was substantially lower in HIV patients [0.48 (95% confidence interval (CI) 0.42–0.55)] compared to the comparison cohort [0.88 (0.86 to 0.90)]. However, in HIV patients with no risk factors (N = 871) the probability of survival was equivalent to that of the general population [0.86 (95% CI 0.77–0.92)]. In contrast, the probability of survival was 0.58 in patients with HIV risk factors (N = 704), 0.30 in patients with comorbidities (N = 479), and 0.03 in patients with drug or alcohol abuse (N = 313).

Conclusions

The increased risk of death in HIV-infected individuals is mainly attributable to risk factors that can be identified prior to or in the initial period of antiretroviral treatment. Mortality in patients without risk factors on a successful HAART is almost identical to that of the non–HIV-infected population.     

Dynamics of Specific Anti-Mycobacterium avium Subsp. paratuberculosis Antibody Response through Age

Mycobacterium avium subsp. paratuberculosis (MAP) causes a chronic infection in cattle. MAP infected cattle with humoral immune (HI) reactions with IgG antibodies are usually those where latency of infection has ceased and their infection is progressing towards reduced milk yield, weight loss and significant bacterial excretion in feces. The proportion of detectable infections among all infected animals that will develop disease is often referred to as ‘the tip of the iceberg’. The purpose of this study was to estimate this proportion. Test-records from 18,972 Danish dairy cows with MAP specific IgG antibodies on their final test-record were used to estimate age-specific sensitivities (Se). These cows were the infected ones considered to develop disease in a population with a representative age-distribution and were defined as cases. The specificity (Sp) of the test was estimated based on test-results from 166,905 cows, which had no MAP IgG antibodies in their final four test-records. The Sp, age-specific Se and maximum Se were used to estimate the probability of having HI at a given age resulting in the proportion of infected cows with HI at a given age. For cows 2 years of age, the proportion of detectable cases was 0.33, while it was 0.94 for cows 5 years of age. Thus, there was a significant shift in the tip of the iceberg with aging. This study provided a model for estimating the proportion of latent chronic infections that would progress to disease, and the results can be used to model infection dynamics.     

Structural gene variants in the porcine mannose-binding lectin 1 (MBL1) gene are associated with low serum MBL-A concentrations

Mannose-binding lectin (MBL) is a collagenous lectin that kills a wide range of pathogenic microbes through complement activation. The MBL1 and MBL2 genes encode MBL-A and MBL-C, respectively. MBL deficiency in humans is associated with higher susceptibility to viral as well as bacterial infections. A number of single nucleotide polymorphisms (SNP) have been identified in the collagen-like domain of the human MBL gene, of which several are strongly associated with decreased concentrations of MBL in serum. In this study, we have identified a number of SNPs in the porcine MBL-A gene. Sequence comparisons identified a total of 14 SNPs, eight of which were found in exons and six in introns. Four of the eight exon-located SNPs were non-synonymous. Sequence data from several Duroc and Landrace pigs identified four different haplotypes. One haplotype was found in Duroc pigs only, and three haplotypes were found in the Landrace pigs. One of the identified haplotypes was associated with low concentration of MBL-A in serum. The concentration of MBL-A in serum was further assessed in a large number of Duroc and Landrace boars to address its correlation with disease frequency. The MBL-A concentration in Duroc boars showed one single population, whereas Landrace boars showed four distinct populations for MBL-A concentration. The Landrace boars were finally assessed for disease incidence, and the association with the concentration of MBL-A in serum was investigated. No association between MBL and disease incidence was found in this study.     

The SNARE protein vti1a functions in dense‐core vesicle biogenesis

The SNARE protein vti1a is proposed to drive fusion of intracellular organelles, but recent data also implicated vti1a in exocytosis. Here we show that vti1a is absent from mature secretory vesicles in adrenal chromaffin cells, but localizes to a compartment near the trans‐Golgi network, partially overlapping with syntaxin‐6. Exocytosis is impaired in vti1a null cells, partly due to fewer Ca²⁺‐channels at the plasma membrane, partly due to fewer vesicles of reduced size and synaptobrevin‐2 content. In contrast, release kinetics and Ca²⁺‐sensitivity remain unchanged, indicating that the final fusion reaction leading to transmitter release is unperturbed. Additional deletion of the closest related SNARE, vti1b, does not exacerbate the vti1a phenotype, and vti1b null cells show no secretion defects, indicating that vti1b does not participate in exocytosis. Long‐term re‐expression of vti1a (days) was necessary for restoration of secretory capacity, whereas strong short‐term expression (hours) was ineffective, consistent with vti1a involvement in an upstream step related to vesicle generation, rather than in fusion. We conclude that vti1a functions in vesicle generation and Ca²⁺‐channel trafficking, but is dispensable for transmitter release.