Colour variation in the peppered moth Biston betularia was long accepted to be under strong natural selection. Melanics were believed to be fitter than pale morphs because of lower predation at ...daytime resting sites on dark, sooty bark. Melanics became common during the industrial revolution, but since 1970 there has been a rapid reversal, assumed to have been caused by predators selecting against melanics resting on today's less sooty bark. Recently, these classical explanations of melanism were attacked, and there has been general scepticism about birds as selective agents. Experiments and observations were accordingly carried out by Michael Majerus to address perceived weaknesses of earlier work. Unfortunately, he did not live to publish the results, which are analysed and presented here by the authors. Majerus released 4864 moths in his six-year experiment, the largest ever attempted for any similar study. There was strong differential bird predation against melanic peppered moths. Daily selection against melanics (s ≃ 0.1) was sufficient in magnitude and direction to explain the recent rapid decline of melanism in post-industrial Britain. These data provide the most direct evidence yet to implicate camouflage and bird predation as the overriding explanation for the rise and fall of melanism in moths.
Alcohol intake is a strong and well established risk factor for oesophageal squamous cell carcinoma (OSCC), but the association with oesophageal adenocarcinoma (OA) or adjacent tumours of the ...oesophagogastric junction (OGJA), remains unclear. Therefore, the association of alcohol intake with OSCC, OA, and OGJA was determined in nine case-control studies and two cohort studies of the Barrett's Esophagus and Esophageal Adenocarcinoma Consortium (BEACON).
Information was collected on alcohol intake, age, sex, education, body mass index, gastro-oesophageal reflux, and tobacco smoking from each study. Along with 10,854 controls, 1821 OA, and 1837 OGJA, seven studies also collected OSCC cases (n=1016). Study specific ORs and 95% CIs were calculated from multivariate adjusted logistic regression models for alcohol intake in categories compared to non-drinkers. Summary risk estimates were obtained by random effects models. Results No increase was observed in the risk of OA or OGJA for increasing levels of any of the alcohol intake measures examined. ORs for the highest frequency category (≥ 7 drinks per day) were 0.97 (95% CI 0.68 to 1.36) for OA and 0.77 (95% CI = 0.54 to 1.10) for OGJA. Suggestive findings linked moderate intake (eg, 0.5 to <1 drink per day) to decreased risk of OA (OR 0.63, 95% CI 0.41 to 0.99) and OGJA (OR 0.78, 95% CI 0.62 to 0.99). In contrast, alcohol intake was strongly associated with increased risk of OSCC (OR for ≥ 7 drinks per day 9.62, 95% CI 4.26 to 21.71).
In contrast to OSCC, higher alcohol consumption was not associated with increased risk of either OA or OGJA. The apparent inverse association observed with moderate alcohol intake should be evaluated in future prospective studies.
The Yarra River Estuary is a salt wedge estuary prone to hypoxia in the bottom waters during low flow periods. Rates of denitrification and dissimilatory nitrate reduction to ammonium (DNRA) were ...quantified using 15N in relation to oxygen, nitrate and available reductants. Denitrification was the dominant nitrate reduction pathway under all oxygen conditions, however, DNRA increased from <1% under hypoxic conditions (<50μmolL−1O2) to ∼18% of total nitrate reduction under oxygen saturation in the water column in intact core incubations. Microprofiles of nitrate reduction pathways in intact cores using diffusive equilibrium in thin layer (DET) gels showed significant rates of DNRA only occurred under oxic conditions in the presence of Fe2+. Cores incubated anoxically, developed free sulfide within the porewater, had very low concentrations of Fe2+ and low rates of DNRA. Slurry incubations with varying concentrations of NO3− showed that denitrifying bacteria had a higher affinity than nitrate ammonifying bacteria with Km values of 49 and 86μmolL−1 for denitrification and DNRA, respectively, however, this could not explain the change in the rates of DNRA relative to denitrification observed. Further slurry incubations to investigate the relationship between DNRA and Fe2+ oxidation were inconclusive and complicated by very high backgrounds of sorbed (HCl extractable) Fe2+. Addition of Fe2+ to the slurry did not stimulate denitrification compared to a control (no Fe2+ addition), however, there was a significant decrease in the Fe2+ concentration over the period where DNRA occurred in the Fe2+ addition treatment, and no significant decrease in the control treatment. The ratio of DNRA to Fe2+ consumption was 15±6 and 7±3 for the Fe2+ and control treatments, respectively. We suggest reduced rates of DNRA under anoxic conditions can be explained by the binding of Fe2+ with free sulfides and the formation of FeS removing available Fe2+ for DNRA.
Accretion-disc precession in UX Ursae Majoris de Miguel, E; Patterson, J; Cejudo, D ...
Monthly Notices of the Royal Astronomical Society,
04/2016, Letnik:
457, Številka:
2
Journal Article
Recenzirano
Odprti dostop
We report the results of a long campaign of time series photometry on the nova-like variable UX Ursae Majoris during 2015. It spanned 150 nights, with ~ 1800 h of coverage on 121 separate nights. The ...star was in its normal 'high state' near magnitude V = 13, with slow waves in the light curve and eclipses every 4.72 h. Remarkably, the star also showed a nearly sinusoidal signal with a full amplitude of 0.44 mag and a period of 3.680 plus or minus 0.007 d. We interpret this as the signature of a retrograde precession (wobble) of the accretion disc. The same period is manifest as a plus or minus 33 s wobble in the timings of mid-eclipse, indicating that the disc's centre of light moves with this period. The star also showed strong 'negative superhumps' at frequencies ... + N and 2... + N, where ... and N are, respectively, the orbital and precession frequencies. It is possible that these powerful signals have been present, unsuspected, throughout the more than 60 yr of previous photometric studies. (ProQuest: ... denotes formulae/symbols omitted.)
The role of permeable sediments and subterranean estuaries as coastal nutrient filters is a question of key interest, particularly in areas with high nitrogen loadings. Here, we evaluated the ...effectiveness of a sandy subterranean estuary in cycling and removing nitrate using stable isotopes of N and O at natural (δ15N-NO₃⁻ and δ18O-NO₃⁻) and enriched levels (15N). Isotopes were used in conjunction with flow through reactors under anoxic conditions to quantify (1) the overall enrichment factor (15ε) of nitrate removal processes which was then applied to estimate the in situ percentage of nitrate removal within the subterranean estuary and (2) the potential rates of denitrification, dissimilatory nitrate reduction to ammonium, and anammox. We found that 15ε varied between −24 and −34‰ and were positively correlated with nitrate concentrations and the percentage of organic carbon added to the sediments. Using these 15ε values in a Rayleigh distillation model resulted in an estimated average of 34% ± 14% nitrate removal within the subterranean estuary, less than half of the percentage estimated using the nitrate-salinity mixing model (66% ± 28%). Denitrification was the most dominant nitrate removal pathway within the subterranean estuary with potential rates among the highest denitrification rates reported for both permeable and cohesive sediments. The contribution of dissimilatory nitrate reduction to ammonium showed significant seasonal variation while the rates of anammox were consistent throughout the study. We suggest that the spatial shift of the subterranean estuary is the most likely explanation for the seasonal differences in the rates of denitrification and dissimilatory nitrate reduction to ammonium.
Stormwater biofiltration systems (also known as biofilters, bioretention, rain gardens) are engineered nature-based solutions, which help mitigate aquatic nitrogen pollution arising from storm ...runoff. These systems are being increasingly used in a range of climates across the world. A decline in treatment performance is frequently observed in cold weather conditions. While plant species comprise an important design factor influencing system performance, the effect of temperature on the fate of dissolved nitrogen forms, namely ammonium (NH4+) and nitrate (NO3−), in the presence of different plant species in these systems remains unclear. A large scale laboratory experiment was undertaken that measured potential rates of nitrification, denitrification and dissimilatory nitrate reduction to ammonium (DNRA) as well as the microbial community structure to investigate nitrogen fate and hence removal under two different temperature conditions (2 °C and 15 °C) in the presence of four distinct plant species. The results indicate that lower nitrification rates (reduced by a factor of 4) coupled with potential media NH4+ desorption could be contributing to reduced NH4+ removal during cold conditions. Planting with species exhibiting good nutrient uptake capacity can reduce the extent of this performance decline. While NO3− reduction generally remains problematic during cold weather (<0 to 55% reduction), which may not be significantly different from warmer periods, the study demonstrated that the denitrification potential and gene abundance (nap, nar, NirS, norB, nosZ) to be higher than those of nitrification (amoA). Denitrification may not proceeding at optimal rates due to lack of conducive environmental conditions. Nitrogen transformation via DNRA was found to be relatively insignificant. Future studies should investigate the potential of employing cold-resilient plant species to maintain both NH4+ and NO3− removal in cold weather conditions.
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•The fate of nitrogen in the presence of four distinct plant species and two temperature conditions was studied.•Biofilter soil denitrification potential 3.5 times higher than corresponding nitrification potential•Nitrification potential was reduced by 4-fold at 2 °C compared to 15 °C.•NOx removal remained low in the presence of species with low-nutrient uptake capacity at both 2 °C and 15 °C.•Required retention time > three days for denitrification under anoxic conditions at 15 °C.
Seagrass meadows form an ecologically important ecosystem in the
coastal zone. The 15N∕14N ratio of seagrass is commonly used to
assess the extent to which sewage-derived nitrogen may be influencing ...seagrass
beds. There have, however, been few studies comparing the 15N∕14N
ratios of seagrass beds, their associated sediments and, of critical
importance, the porewater NH4+ pool, which is most bioavailable.
Here, we undertook a study of the 15N∕14N ratios of seagrass
tissue, sediment porewater NH4+ pool and the bulk sediment to
elucidate the extent of any fractionating processes taking place during
organic matter mineralisation and nitrogen assimilation. The study was
undertaken within two coastal embayments known to receive nitrogen from a
range of sources including marine, urban and sewage sources. There was close
agreement between the bulk sediment δ15N and seagrass
δ15N (r2 of 0.92 and mean offset of 0.9 ‰),
illustrating a close coupling between the plant and sediment pools. The
δ15N of porewater NH4+ was strongly correlated with
the δ15N of both the sediment and the seagrass tissue. For both of
these relationships, however, the intercept of the line was not significantly
different from 0 and the slopes were not 1:1, reflecting an enrichment of
the porewater NH4+ δ15N pool relative to seagrass
tissue and bulk sediment δ15N at high δ15N values. We
suggest that nitrogen fixation is the most likely explanation for the
observation that the δ15N of seagrass tissue is lower than
porewater NH4+. Conversely, we suggest that the most likely
explanation for the enrichment of porewater NH4+ above bulk
sediment was through the preferential mineralisation of isotopically enriched
algal material (nitrogen derived from sewage sources) within the sediment as
δ15N increased in the vicinity of a sewage treatment plant.
Permeable (sandy) sediments cover half of the continental margin and are major regulators of oceanic carbon cycling. The microbial communities within these highly dynamic sediments frequently shift ...between oxic and anoxic states, and hence are less stratified than those in cohesive (muddy) sediments. A major question is, therefore, how these communities maintain metabolism during oxic-anoxic transitions. Here, we show that molecular hydrogen (H
) accumulates in silicate sand sediments due to decoupling of bacterial fermentation and respiration processes following anoxia. In situ measurements show that H
is 250-fold supersaturated in the water column overlying these sediments and has an isotopic composition consistent with fermentative production. Genome-resolved shotgun metagenomic profiling suggests that the sands harbour diverse and specialized microbial communities with a high abundance of NiFe-hydrogenase genes. Hydrogenase profiles predict that H
is primarily produced by facultatively fermentative bacteria, including the dominant gammaproteobacterial family Woeseiaceae, and can be consumed by aerobic respiratory bacteria. Flow-through reactor and slurry experiments consistently demonstrate that H
is rapidly produced by fermentation following anoxia, immediately consumed by aerobic respiration following reaeration and consumed by sulfate reduction only during prolonged anoxia. Hydrogenotrophic sulfur, nitrate and nitrite reducers were also detected, although contrary to previous hypotheses there was limited capacity for microalgal fermentation. In combination, these experiments confirm that fermentation dominates anoxic carbon mineralization in these permeable sediments and, in contrast to the case in cohesive sediments, is largely uncoupled from anaerobic respiration. Frequent changes in oxygen availability in these sediments may have selected for metabolically flexible bacteria while excluding strict anaerobes.
The fate of diazotrophic nitrogen (N(D)) fixed by planktonic cyanobacteria in pelagic food webs remains unresolved, particularly for toxic cyanophytes that are selectively avoided by most herbivorous ...zooplankton. Current theory suggests that N(D) fixed during cyanobacterial blooms can enter planktonic food webs contemporaneously with peak bloom biomass via direct grazing of zooplankton on cyanobacteria or via the uptake of bioavailable N(D) (exuded from viable cyanobacterial cells) by palatable phytoplankton or microbial consortia. Alternatively, N(D) can enter planktonic food webs post-bloom following the remineralization of bloom detritus. Although the relative contribution of these processes to planktonic nutrient cycles is unknown, we hypothesized that assimilation of bioavailable N(D) (e.g., nitrate, ammonium) by palatable phytoplankton and subsequent grazing by zooplankton (either during or after the cyanobacterial bloom) would be the primary pathway by which N(D) was incorporated into the planktonic food web. Instead, in situ stable isotope measurements and grazing experiments clearly documented that the assimilation of N(D) by zooplankton outpaced assimilation by palatable phytoplankton during a bloom of toxic Nodularia spumigena Mertens. We identified two distinct temporal phases in the trophic transfer of N(D) from N. spumigena to the plankton community. The first phase was a highly dynamic transfer of N(D) to zooplankton with rates that covaried with bloom biomass while bypassing other phytoplankton taxa; a trophic transfer that we infer was routed through bloom-associated bacteria. The second phase was a slowly accelerating assimilation of the dissolved-N(D) pool by phytoplankton that was decoupled from contemporaneous variability in N. spumigena concentrations. These findings provide empirical evidence that N(D) can be assimilated and transferred rapidly throughout natural plankton communities and yield insights into the specific processes underlying the propagation of N(D) through pelagic food webs.
Water treatment wetlands are increasingly being used to reduce pollutant loads including nitrogen (N) in urban runoff. Processes such as denitrification (DNF) and anaerobic ammonium oxidation ...(anammox), which remove N, and dissimilatory nitrate reduction to ammonium (DNRA), which recycles N, play an important role in controlling NOx (NO₃⁻ + NO₂⁻) removal versus recycling in wetlands. The relative importance of DNF, anammox and DNRA was investigated in four constructed stormwater urban wetlands in Melbourne, Australia. Rates of DNF and DNRA were variable and did not differ significantly among wetlands. However, rates of DNF and DNRA were significantly different (p < 0.05) in different seasons. The relationship between NOx reduction processes and measured concentrations of water column NOx, chlorophyll a (chl-a), sediment organic carbon (OC), porewater ferrous iron (Fe₂⁺) and sulfide (S²⁻) and water column temperature were examined using multiple regression analysis (MRA). Anammox was an insignificant pathway (< 0.05% of total nitrate reduction). During winter when average water column temperatures were 12 °C, DNRA was consistently higher than DNF averaging 67 ± 23% of total NOx reduction. The MRA revealed that DNF was positively associated with NOx concentration whereas DNRA was negatively associated with temperature, and porewater Fe₂⁺, and positively associated with chl-a. The ratio between DNF and DNF:(DNF + DNRA) showed a positive correlation with both temperature and NOx concentration in the MRA. At higher temperatures and higher NOx concentrations, DNF increased over DNRA. Overall, this study suggests that at low NOx concentrations, N is recycled internally in these urban stormwater wetlands, but the portion of N removed by DNF increases as NOx concentrations increase.
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