Climate structuring of Batrachochytrium dendrobatidis infection in the threatened amphibians of the northern Western Ghats, India

Batrachochytrium dendrobatidis (Bd) is a pathogen killing amphibians worldwide. Its impact across much of Asia is poorly characterized. This study systematically surveyed amphibians for Bd across rocky plateaus in the northern section of the Western Ghats biodiversity hotspot, India, including the first surveys of the plateaus in the coastal region. These ecosystems offer an epidemiological model system since they are characterized by differing levels of connectivity, edaphic and climatic conditions, and anthropogenic stressors. One hundred and eighteen individuals of 21 species of Anura and Apoda on 13 plateaus ranging from 67 to 1179 m above sea level and 15.89 to 17.92° North latitude were sampled. Using qPCR protocols, 79% of species and 27% of individuals tested were positive for Bd. This is the first record of Bd in caecilians in India, the Critically Endangered Xanthophryne tigerina and Endangered Fejervarya cf. sahyadris. Mean site prevalence was 28.15%. Prevalence below the escarpment was 31.2% and 25.4% above. The intensity of infection (GE) showed the reverse pattern. Infection may be related to elevational temperature changes, thermal exclusion, inter-site connectivity and anthropogenic disturbance. Coastal plateaus may be thermal refuges from Bd. Infected amphibians represented a wide range of ecological traits posing interesting questions about transmission routes

Propensity scores in the presence of effect modification: A case study using the comparison of mortality on hemodialysis versus peritoneal dialysis

Purpose. To control for confounding bias from non-random treatment assignment in observational data, both traditional multivariable models and more recently propensity score approaches have been applied. Our aim was to compare a propensity score-stratified model with a traditional multivariable-adjusted model, specifically in estimating survival of hemodialysis (HD) versus peritoneal dialysis (PD) patients. Methods. Using the Dutch End-Stage Renal Disease Registry, we constructed a propensity score, predicting PD assignment from age, gender, primary renal disease, center of dialysis, and year of first renal replacement therapy. We developed two Cox proportional hazards regression models to estimate survival on PD relative to HD, a propensity score-stratified model stratifying on the propensity score and a multivariable-adjusted model, and tested several interaction terms in both models. Results. The propensity score performed well: it showed a reasonable fit, had a good c-statistic, calibrated well and balanced the covariates. The main-effects multivariable-adjusted model and the propensity score-stratified univariable Cox model resulted in similar relative mortality risk estimates of PD compared with HD (0.99 and 0.97, respectively) with fewer significant covariates in the propensity model. After introducing the missing interaction variables for effect modification in both models, the mortality risk estimates for both main effects and interactions remained comparable, but the propensity score model had nearly as many covariates because of the additional interaction variables. Conclusion. Although the propensity score performed well, it did not alter the treatment effect in the outcome model and lost its advantage of parsimony in the presence of effect modification

Direct and Indirect Induction of a Compensatory Phenotype that Alleviates the Costs of an Inducible Defense

Organisms often exhibit phenotypic plasticity in multiple traits in response to impending environmental change. Multiple traits phenotypic plasticity is complex syndrome brought on by causal relations in ecological and physiological context. Larvae of the salamander Hynobius retardatus exhibit inducible phenotypic plasticity of two traits, when at risk of predation by dragonfly larvae. One induced phenotype is an adaptive defense behaviour, i.e., stasis at the bottom of water column, directly triggered by the predation risk. Another one is a compensatory phenotype, i.e., enlarged external gills, for an unavoidable cost (hypoxia) associated with the induced defense. We identified two ways by which this compensatory phenotype could be induced. The compensatory phenotype is induced in response to not only the associated hypoxic conditions resulting from the induced defense but also the most primary but indirect cause, presence of the predator

Non-Linear Interactions between Consumers and Flow Determine the Probability of Plant Community Dominance on Maine Rocky Shores

Although consumers can strongly influence community recovery from disturbance, few studies have explored the effects of consumer identity and density and how they may vary across abiotic gradients. On rocky shores in Maine, recent experiments suggest that recovery of plant- or animal- dominated community states is governed by rates of water movement and consumer pressure. To further elucidate the mechanisms of consumer control, we examined the species-specific and density-dependent effects of rocky shore consumers (crabs and snails) on community recovery under both high (mussel dominated) and low flow (plant dominated) conditions. By partitioning the direct impacts of predators (crabs) and grazers (snails) on community recovery across a flow gradient, we found that grazers, but not predators, are likely the primary agent of consumer control and that their impact is highly non-linear. Manipulating snail densities revealed that herbivorous and bull-dozing snails (Littorina littorea) alone can control recovery of high and low flow communities. After ∼1.5 years of recovery, snail density explained a significant amount of the variation in macroalgal coverage at low flow sites and also mussel recovery at high flow sites. These density-dependent grazer effects were were both non-linear and flow-dependent, with low abundance thresholds needed to suppress plant community recovery, and much higher levels needed to control mussel bed development. Our study suggests that consumer density and identity are key in regulating both plant and animal community recovery and that physical conditions can determine the functional forms of these consumer effects

Pathogen-induced hatching and population-specific life-history response to water-borne cues in brown trout (Salmo trutta)

Hatching is an important niche shift, and embryos in a wide range of taxa can either accelerate or delay this life-history switch in order to avoid stage-specific risks. Such behavior can occur in response to stress itself and to chemical cues that allow anticipation of stress. We studied the genetic organization of this phenotypic plasticity and tested whether there are differences among populations and across environments in order to learn more about the evolutionary potential of stress-induced hatching. As a study species, we chose the brown trout (Salmo trutta; Salmonidae). Gametes were collected from five natural populations (within one river network) and used for full-factorial in vitro fertilizations. The resulting embryos were either directly infected with Pseudomonas fluorescens or were exposed to waterborne cues from P. fluorescens-infected conspecifics. We found that direct inoculation with P. fluorescens increased embryonic mortality and induced hatching in all host populations. Exposure to waterborne cues revealed population-specific responses. We found significant additive genetic variation for hatching time, and genetic variation in trait plasticity. In conclusion, hatching is induced in response to infection and can be affected by waterborne cues of infection, but populations and families differ in their reaction to the latter

Behaviourally Mediated Phenotypic Selection in a Disturbed Coral Reef Environment

Natural and anthropogenic disturbances are leading to changes in the nature of many habitats globally, and the magnitude and frequency of these perturbations are predicted to increase under climate change. Globally coral reefs are one of the most vulnerable ecosystems to climate change. Fishes often show relatively rapid declines in abundance when corals become stressed and die, but the processes responsible are largely unknown. This study explored the mechanism by which coral bleaching may influence the levels and selective nature of mortality on a juvenile damselfish, Pomacentrus amboinensis, which associates with hard coral. Recently settled fish had a low propensity to migrate small distances (40 cm) between habitat patches, even when densities were elevated to their natural maximum. Intraspecific interactions and space use differ among three habitats: live hard coral, bleached coral and dead algal-covered coral. Large fish pushed smaller fish further from the shelter of bleached and dead coral thereby exposing smaller fish to higher mortality than experienced on healthy coral. Small recruits suffered higher mortality than large recruits on bleached and dead coral. Mortality was not size selective on live coral. Survival was 3 times as high on live coral as on either bleached or dead coral. Subtle behavioural interactions between fish and their habitats influence the fundamental link between life history stages, the distribution of phenotypic traits in the local population and potentially the evolution of life history strategies

Chiropractic and self-care for back-related leg pain: design of a randomized clinical trial

<p>Abstract</p> <p>Background</p> <p>Back-related leg pain (BRLP) is a common variation of low back pain (LBP), with lifetime prevalence estimates as high as 40%. Often disabling, BRLP accounts for greater work loss, recurrences, and higher costs than uncomplicated LBP and more often leads to surgery with a lifetime incidence of 10% for those with severe BRLP, compared to 1-2% for those with LBP.</p> <p>In the US, half of those with back-related conditions seek CAM treatments, the most common of which is chiropractic care. While there is preliminary evidence suggesting chiropractic spinal manipulative therapy is beneficial for patients with BRLP, there is insufficient evidence currently available to assess the effectiveness of this care.</p> <p>Methods/Design</p> <p>This study is a two-site, prospective, parallel group, observer-blinded randomized clinical trial (RCT). A total of 192 study patients will be recruited from the Twin Cities, MN (n = 122) and Quad Cities area in Iowa and Illinois (n = 70) to the research clinics at WHCCS and PCCR, respectively.</p> <p>It compares two interventions: chiropractic spinal manipulative therapy (SMT) plus home exercise program (HEP) to HEP alone (minimal intervention comparison) for patients with subacute or chronic back-related leg pain.</p> <p>Discussion</p> <p>Back-related leg pain (BRLP) is a costly and often disabling variation of the ubiquitous back pain conditions. As health care costs continue to climb, the search for effective treatments with few side-effects is critical. While SMT is the most commonly sought CAM treatment for LBP sufferers, there is only a small, albeit promising, body of research to support its use for patients with BRLP.</p> <p>This study seeks to fill a critical gap in the LBP literature by performing the first full scale RCT assessing chiropractic SMT for patients with sub-acute or chronic BRLP using important <b>patient-oriented </b>and <b>objective biomechanical </b>outcome measures.</p> <p>Trial Registration</p> <p>ClinicalTrials.gov <a href="http://www.clinicaltrials.gov/ct2/show/NCT00494065">NCT00494065</a></p

Interactive effects of pesticide exposure and habitat structure on behavior and predation of a marine larval fish

Coastal development has generated multiple stressors in marine and estuarine ecosystems, including habitat degradation and pollutant exposure, but the effects of these stressors on the ecology of fishes remain poorly understood. We studied the separate and combined effects of an acute 4 h sublethal exposure of the pyrethroid pesticide esfenvalerate and structural habitat complexity on behavior and predation risk of larval topsmelt (Atherinops affinis). Larvae were exposed to four nominal esfenvalerate concentrations (control, 0.12, 0.59, 1.18 μg/L), before placement into 12 L mesocosms with a three-spine stickleback (Gasterosteus aculeatus) predator. Five treatments of artificial eelgrass included a (1) uniform and (2) patchy distribution of eelgrass at a low density (500 shoots per m(2)), a (3) uniform and (4) patchy distribution of eelgrass at a high density (1,000 shoots per m(2)), and (5) the absence of eelgrass. The capture success of predators and aggregative behavior of prey were observed in each mesocosm for 10 min of each trial, and mortality of prey was recorded after 60 min. Exposure to esfenvalerate increased the proportion of larvae with swimming abnormalities. Surprisingly, prey mortality did not increase linearly with pesticide exposure but increased with habitat structure (density of eelgrass), which may have been a consequence of compensating predator behavior. The degree of prey aggregation decreased with both habitat structure and pesticide exposure, suggesting that anti-predator behaviors by prey may have been hampered by the interactive effects of both of these factors