Emerging diseases are impacting animals under high‐density culture, yet few studies assess their importance to wild populations. Microparasites selected for enhanced virulence in culture settings ...should be less successful maintaining infectivity in wild populations, as once the host dies, there are limited opportunities to infect new individuals. Instead, moderately virulent microparasites persisting for long periods across multiple environments are of greatest concern. Evolved resistance to endemic microparasites may reduce susceptibilities, but as barriers to microparasite distributions are weakened, and environments become more stressful, unexposed populations may be impacted and pathogenicity enhanced. We provide an overview of the evolutionary and ecological impacts of infectious diseases in wild salmon and suggest ways in which modern technologies can elucidate the microparasites of greatest potential import. We present four case studies that resolve microparasite impacts on adult salmon migration success, impact of river warming on microparasite replication, and infection status on susceptibility to predation. Future health of wild salmon must be considered in a holistic context that includes the cumulative or synergistic impacts of multiple stressors. These approaches will identify populations at greatest risk, critically needed to manage and potentially ameliorate the shifts in current or future trajectories of wild populations.
Blooms of
Cochlodinium
sp., monitored for the first time on the west coast of Vancouver Island from August to October 1999, caused substantial mortality to farmed salmon, accounting for economic ...losses of about CAN $2 million. Cells of the alga were 25-40 μm long, 20-30 μm wide and had a torsion of 1.8 to 2 turns. Pairs of cells were common, forming up to 25% of the biomass; apart from the absence of longer chains, the morphology of the species, including the anteriorly placed nucleus and numerous golden chloroplasts, matched the gross morphological description of
Cochlodinium polykrikoides
. A strong diurnal pattern was observed in blooms at farm sites, with high cell concentrations overnight at depths of up to 25 m and dense surface blooms during the day. Surface concentrations of up to 60,000 cells ml
−1
peaked in early September. Fish stopped feeding when cell counts exceeded 500 cells ml
−1
in the net-pens, and mortality was observed above 2000 cells ml
−1
. Bioassays in the field with Atlantic salmon (
Salmo salar
) smolts demonstrated lethality after 120 min exposure and over 90% mortality after 500 min, when cell concentrations varied from 10,800 to 2700 cells ml
−1
as the bloom moved through the test site. Under controlled laboratory conditions,
S. salar
smolts died within 27 min of exposure to 7200 cells ml
−1
and 55 min with 3400 cells ml
−1
; although fish appeared distressed at 1000 cells ml
−1
, only 20% died within the 24 h bioassay. Enhanced toxicity of
Cochlodinium
sp., observed when the dinoflagellate was oxygenated or aerated, may have been a function of agitation, leading to increased release of lethal reactive oxygen species. Mitigation protocols of net-pen enclosures, with 14 m deep tarps and upwelling of deep water by aeration, proved less effective against
Cochlodinium
sp. than for
Heterosigma akashiwo
, the major harmful algal bloom killer of farmed salmon on the west coast of Canada.
Using 7.3 fb⁻¹ of pp collisions collected by the D0 detector at the Fermilab Tevatron, we measure the distribution of the variable φ(η)*, which probes the same physical effects as the Z/γ* boson ...transverse momentum, but is less susceptible to the effects of experimental resolution and efficiency. A QCD prediction is found to describe the general features of the φ(η)* distribution, but is unable to describe its detailed shape or dependence on boson rapidity. A prediction that includes a broadening of transverse momentum for small values of the parton momentum fraction is strongly disfavored.
We determine the fraction of tt events with spin correlation, assuming that the spin of the top quark is either correlated with the spin of the top antiquark as predicted by the standard model or is ...uncorrelated. For the first time we use a matrix-element-based approach to study tt spin correlation. We use tt → W+ b W- b → ℓ+ νbℓ- ν b final states produced in pp collisions at a center-of-mass energy sqrt(s)=1.96 TeV, where ℓ denotes an electron or a muon. The data correspond to an integrated luminosity of 5.4 fb(-1) and were collected with the D0 detector at the Fermilab Tevatron collider. The result agrees with the standard model prediction. We exclude the hypothesis that the spins of the tt are uncorrelated at the 97.7% C.L.
We present the results of the combination of searches for the standard model Higgs boson produced in association with a W or Z boson and decaying into bb using the data sample collected with the D0 ...detector in pp collisions at √s = 1.96 TeV at the Fermilab Tevatron Collider. We derive 95% C.L. upper limits on the Higgs boson cross section relative to the standard model prediction in the mass range 100 GeV ≤ M(H) ≤ 150 GeV, and we exclude Higgs bosons with masses smaller than 102 GeV at the 95% C.L. In the mass range 120 GeV ≤ M(H) ≤145 GeV, the data exhibit an excess above the background prediction with a global significance of 1.5 standard deviations, consistent with the expectation in the presence of a standard model Higgs boson.
We study WW and WZ production with ℓνqq (ℓ=e,μ) final states using data collected by the D0 detector at the Fermilab Tevatron Collider corresponding to 4.3 fb(-1) of integrated luminosity from pp ...collisions at sqrts=1.96 TeV. Assuming the ratio between the production cross sections σ(WW) and σ(WZ) as predicted by the standard model, we measure the total WV (V=W,Z) cross section to be σ(WV)=19.6(-3.0)(+3.2) pb and reject the background-only hypothesis at a level of 7.9 standard deviations. We also use b-jet discrimination to separate the WZ component from the dominant WW component. Simultaneously fitting WW and WZ contributions, we measure σ(WW)=15.9(-3.2)(+3.7) pb and σ(WZ)=3.3(-3.3)(+4.1) pb, which is consistent with the standard model predictions.
The physiological effects of domoic acid on the immune system of marine invertebrates, which are known to accumulate this neurotoxin, have not been investigated previously. Changes in the number and ...relative phagocytic activity of circulating haemocytes in
Crassostrea gigas exposed to domoic acid in the diatom
Pseudonitzschia pungens f.
multiseries for 48 hr, followed by clearance for 240 hr, were investigated using chemiluminescence. An initial stress response to the toxin assimilation was characterized by a marked increase in number and activity of haemocytes with 4 hr of exposure to the algae. Although the toxin level in the oyster increased during the 48 hr exposure, both number and activity of haemocytes declined from the 4 hr peak values to those significantly lower than control values after 24 hr clearance. This suppression in number and activity of circulating haemocytes following the initial toxin response was rectified only after 48 hr clearance, when domoic acid levels in the oyster tissue had declined to trace levels, allowing blood cells to regain their normal characteristics.
We report the observation of a narrow structure, $X(5568)$, in the decay sequence $X(5568) \rightarrow B_s^0 \pi^{\pm}$, $B_s^0 \rightarrow J/\psi \phi$, $J/\psi\rightarrow \mu^+ \mu^-$, $\phi ...\rightarrow K^+K^-$. This is the first observation of a hadronic state with valence quarks of four different flavors. The mass and natural width of the new state are measured to be $m = 5567.8 \pm 2.9 {\rm \thinspace (stat)} ^{+0.9}_{-1.9} {\rm \thinspace (syst)}$ MeV/$c^2$ and $\Gamma = 21.9 \pm 6.4 {\rm \thinspace (stat)} ^{+5.0}_{-2.5} {\rm \thinspace (syst)} $ MeV/$c^2$, and the significance including look-elsewhere effect and systematic uncertainties is 5.1$\sigma$. The observation is based on$10.4~\rm{fb^{-1}}$ of $p \overline p $ collision data at $\sqrt{s}$ = 1.96 TeV collected by the D0 experiment at the Fermilab Tevatron collider.
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