Extinction hazards in experimental Daphnia magna populations: effects of genotype diversity and environmental variation

Extinction is ubiquitous in natural systems and the ultimate fate of all biological populations. However, the factors that contribute to population extinction are still poorly understood, particularly genetic diversity and composition. A laboratory experiment was conducted to examine the influences of environmental variation and genotype diversity on persistence in experimental Daphnia magna populations. Populations were initiated in two blocks with one, two, three, or six randomly selected and equally represented genotypes, fed and checked for extinction daily, and censused twice weekly over a period of 170 days. Our results show no evidence for an effect of the number of genotypes in a population on extinction hazard. Environmental variation had a strong effect on hazards in both experimental blocks, but the direction of the effect differed between blocks. In the first block, variable environments hastened extinction, while in the second block, hazards were reduced under variable food input. This occurred despite greater fluctuations in population size in variable environments in the second block of our experiment. Our results conflict with previous studies, where environmental variation consistently increased extinction risk. They are also at odds with previous studies in other systems that documented significant effects of genetic diversity on population persistence. We speculate that the lack of sexual reproduction, or the phenotypic similarity among our experimental lines, might underlie the lack of a significant effect of genotype diversity in our study

Rapid Emergence of Co-colonization with Community-acquired and Hospital-Acquired Methicillin-Resistant Staphylococcus aureus Strains in the Hospital Setting

Background: Community-acquired methicillin-resistant Staphylococcus aureus (CAMRSA), a novel strain of MRSA, has recently emerged and rapidly spread in the community. Invasion into the hospital setting with replacement of the hospital-acquired MRSA (HA-MRSA) has also been documented. Co-colonization with both CA-MRSA and HA-MRSA would have important clinical implications given differences in antimicrobial susceptibility profiles and the potential for exchange of genetic information. Methods: A deterministic mathematical model was developed to characterize the transmission dynamics of HA-MRSA and CA-MRSA in the hospital setting and to quantify the emergence of co-colonization with both strains Results: The model analysis shows that the state of co-colonization becomes endemic over time and that typically there is no competitive exclusion of either strain. Increasing the length of stay or rate of hospital entry among patients colonized with CA-MRSA leads to a rapid increase in the co-colonized state. Compared to MRSA decolonization strategy, improving hand hygiene compliance has the greatest impact on decreasing the prevalence of HA-MRSA, CA-MRSA and the co-colonized state. Conclusions: The model predicts that with the expanding community reservoir of CA-MRSA, the majority of hospitalized patients will become colonized with both CA-MRSA and HA-MRSA

The effect of co-colonization with community-acquired and hospital-acquired methicillin-resistant Staphylococcus aureus strains on competitive exclusion

We investigate the in-hospital transmission dynamics of two methicillin-resistant Staphylococcus aureus(MRSA) strains: hospital-acquired methicillin resistant S. aureus (HA-MRSA) and community-acquired methicillin-resistant S. aureus (CA-MRSA). Under the assumption that patients can only be colonized with one strain of MRSA at a time, global results show that competitive exclusion occurs between HA-MRSA and CA-MRSA strains; the strain with the larger basic reproduction ratio will become endemic while the other is extinguished due to competition. Because new studies suggest that patients can be concurrently colonized with multiple strains of MRSA, we extend the model to allow patients to be co-colonized with HA-MRSA and CA-MRSA. Using the extended model, we explore the effect of co-colonization on competitive exclusion by determining the invasion reproduction ratios of the boundary equilibria. In contrast to results derived from the assumption that co-colonization does not occur, the extended model rarely exhibits competitive exclusion. More commonly, both strains become endemic in the hospital. When transmission rates are assumed equal and decolonization measures act equally on all strains, competitive exclusion never occurs. Other interesting phenomena are exhibited. For example, solutions can tend toward a co-existence equilibrium, even when the basic reproduction ratio of one of the strains is less than one

Oxygen consumption in the fathead minnow (Pimephales promelas rafinesque)--II effects of pH, osmotic pressure, and light level

1. 1. There is a curvilinear relationship between oxygen consumption (OC in cm3/g1.053 per hr) and pH, yielding the equation: OC = -0.0612(pH)2 + 1.0478(pH) - 4.051.2. 2. The relationship between OC and osmotic pressure (OP in mOsm/kg) for natural water is shown by the equation: OC = 0.0091(OP)2 - 0.0436(OP) + 0.208, and that for NaCl treated water by: OC = 0.0009(OP)3 - 0.0208(OP)2 + 0.104(OP) + 0.190.3. 3. A significant relationship was exhibited between oxygen consumption and light intensity (LI in W/m2), producing the line given by: OC = 0.0026(LI) + 0.336.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/23753/1/0000726.pd

Oxygen consumption in the fathead minnow (Pimephales promelas rafinesque)-I : Effects of weight, temperature, group size, oxygen level and opercular movement rate as a function of temperature1

1. 1. A relationship is evident between oxygen consumption (OC in cm3/hr) and weight (WT in g) such that: OC = -0.580 (WT)1.0532. 2. Fathead minnows failed to exhibit immediate rate compensation as a result of acute temperature changes. Minnows showed an exponential increase in weight-specific oxygen consumption with temperature (in [deg]C), resulting in a Q10 of over three. The equation is: OC = 100.0482 (Temp.) - 1.268.3. 3. Minnows acclimated to water temperatures of 5-21[deg]C showed a steady increase in opercular movement rates (OMR) (ventilation rates) as expressed by the equation: OMR = 0.1968 (Temp.)2 + 1.064.4. 4. Grouping more than two fish per chamber resulted in an increase in oxygen consumption. The relationship of group size (GS) to oxygen consumption is: OC = 0.04059 (GS)2 - 0.2017 (GS) + 0.5353.5. 5. Oxygen consumption is a function of dissolved oxygen level. This relationship is shown by the equation: OC = 0.003049 (OL)3 - 0.06359 (OL)2 + 0.4211 (OL) - 0.4020 where OL is oxygen level. Due to high variability, it is statistically impossible to determine oxygen level ranges in which they conformed and those in which they regulated.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/23722/1/0000694.pd

Genetic Estimates of Population Age in the Water Flea, Daphnia magna

Genetic datasets can be used to date evolutionary events, even on recent time scales if sufficient data are available. We used statistics calculated from multilocus microsatellite datasets to estimate population ages in data generated through coalescent simulations and in samples from populations of known age in a metapopulation of Daphnia magna in Finland. Our simulation results show that age estimates improve with additional loci and define a time frame over which these statistics are most useful. On the most recent time scales, assumptions regarding the model of mutation (infinite sites vs. stepwise mutation) have little influence on estimated ages. In older populations, size homoplasy among microsatellite alleles results in a downwards bias for estimates based on the infinite sites model (ISM). In the Finnish D. magna metapopulation, our genetically derived estimated ages were biased upwards. Potential sources of this bias include the underlying model of mutation, gene flow, founder size, and the possibility of persistent source populations in the system. Our simulated data show that genetic age estimation is possible, even for very young populations, but our empirical data highlight the importance of factors such as migration when these statistics are applied in natural population

HIV Seroprevalence among Tuberculosis Patients in India, 2006–2007

BACKGROUND: Little information exists regarding the burden of HIV among tuberculosis patients in India, and no population-based surveys have been previously reported. A community-based HIV prevalence survey was conducted among tuberculosis patients treated by the national tuberculosis control programme to evaluate the HIV prevalence among tuberculosis patients in India. METHODOLOGY/PRINCIPAL FINDINGS: Fifteen districts (total population: 40.2 million) across 8 states were stratified by HIV prevalence in antenatal clinic HIV surveillance sites and randomly selected. From December 2006 to May 2007, remnant serum was collected from patients' clinical specimens taken after 2 months of anti-tuberculosis treatment and subjected to anonymous, unlinked HIV testing. Specimens were obtained and successfully tested for 5,995 (73%) of 8,217 tuberculosis patients eligible for the survey. HIV prevalence ranged widely among the 15 surveyed districts, from 1% in Koch Bihar, West Bengal, to 13.8% in Guntur, Andhra Pradesh. HIV infection was 1.3 times more likely among male TB patients than among female patients. Relative to smear-positive tuberculosis, HIV infection was 1.4 times more likely among smear-negative patients and 1.3 times more likely among extrapulmonary patients. In 4 higher-HIV prevalence districts, which had been previously surveyed in 2005-2006, no significant change in HIV prevalence was detected. CONCLUSIONS: The burden of HIV among tuberculosis patients varies widely in India. Programme efforts to implement comprehensive TB-HIV services should be targeted to areas with the highest HIV burden. Surveillance through routine reporting or special surveys is necessary to detect areas requiring intensification of TB-HIV collaborative activities

Linking HIV-Infected TB Patients to Cotrimoxazole Prophylaxis and Antiretroviral Treatment in India

BACKGROUND:HIV-infected persons suffering from tuberculosis experience high mortality. No programmatic studies from India have documented the delivery of mortality-reducing interventions, such as cotrimoxazole prophylactic treatment (CPT) and antiretroviral treatment (ART). To guide TB-HIV policy in India we studied the effectiveness of delivering CPT and ART to HIV-infected persons treated for tuberculosis in three districts in Andhra Pradesh, India, and evaluated factors associated with death. METHODS AND FINDINGS:We retrospectively abstracted data for all HIV-infected tuberculosis patients diagnosed from March 2007 through August 2007 using standard treatment outcome definitions. 734 HIV-infected tuberculosis patients were identified; 493 (67%) were males and 569 (80%) were between the ages of 24-44 years. 710 (97%) initiated CPT, and 351 (50%) collected >60% of their monthly cotrimoxazole pouches provided throughout TB treatment. Access to ART was documented in 380 (51%) patients. Overall 130 (17%) patients died during TB treatment. Patients receiving ART were less likely to die (adjusted hazard ratio [HR] 0.4, 95% confidence interval [CI] 0.3-0.6), while males and those with pulmonary TB were more likely to die (HR 1.7, 95% CI 1.1-2.7, and HR 1.9, 95% CI 1.1-3.2 respectively). CONCLUSIONS:Among HIV-infected TB patients in India death was common despite the availability of free cotrimoxazole locally and ART from referral centres. Death was strongly associated with the absence of ART during TB treatment. To minimize death, programmes should promote high levels of ART uptake and closely monitor progress in implementation

Bioenergetics of the cave cricket, Hadenoecus subterraneus

1. 1. In late spring, cave crickets in Mammoth Cave National Park were investigated in order that their bioenergetics might be elucidated.2. 2. A predictive relation between crop-empty live weight and hind femur length independent of sex was found.3. 3. Long-term weight loss patterns were 1.55 and 1.19mg/hr for females and males, respectively, suggesting feeding intervals of 11.5 and 9.9 days.4. 4. Calorific assimilation efficiencies were found to be 80.4% for females and 82.5% for males.5. 5. The estimated maximal metabolic rates were half that expected for insects of similar mass.6. 6. The mixed waste calorific levels were found to be exceptionally low.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/26417/1/0000504.pd

Water budgets of cave crickets, Hadenoecus subterraneus and camel crickets, Ceuthophilus stygius

1. 1. Studies of cave and camel crickets from cave entrances in Mammoth Cave National Park have produced estimates of total water budgets and component contributions to water balance.2. 2. Weight specific (mg/g crop-free live weight/hr) total water loss (3.200 vs 2.220) and water gained in food (2.393 vs 1.902) are greater in cave than in camel crickets, respectively.3. 3. Weight specific evaporative water loss in both humid, still air (2.269 vs 1.325) and dry, moving air (15.28 vs 9.85) is greater in cave than in camel crickets, respectively.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/26939/1/0000505.pd