Modelling the effect of size on the aerial dispersal of microorganisms

Aim We investigate the long‐standing question of whether the small size of microbes allows most microbial species to colonize all suitable sites around the globe or whether their ranges are limited by opportunities for dispersal. In this study we use a modelling approach to investigate the effect of size on the probability of between‐continent dispersal using virtual microorganisms in a global model of the Earth’s atmosphere. Location Global. Methods We use a computer model of global atmospheric circulation to investigate the effect of microbe size (effective diameters of 9, 20, 40 and 60 μm) on the probability of aerial dispersal. Results We found that for smaller microbes, once airborne, dispersal is remarkably successful over a 1‐year period. The most striking results are the extensive within‐hemisphere distribution of virtual microbes of 9 and 20 μm diameter and the lack of dispersal between the Northern and Southern Hemispheres during the year‐long time‐scale of our simulations. Main conclusions Above a diameter of 20 μm wind dispersal of virtual microbes between continents becomes increasingly unlikely, and it does not occur at all (within our simulated 1‐year period) for those of 60 μm diameter. Within our simulation, the success of small microbes in long‐distance dispersal is due both to their greater abundance and to their longer time in the atmosphere – once airborne – compared with larger microbes.     

Evidence for increases in vegetation species richness across UK Environmental Change Network sites linked to changes in air pollution and weather patterns

We analysed trends in vegetation monitored at regular intervals over the past two decades (1993–2012) at the twelve terrestrial Environmental Change Network (ECN) sites. We sought to determine the extent to which flora had changed and link any such changes to potential environmental drivers. We observed significant increases in species richness, both at a whole network level, and when data were analysed within Broad Habitat groupings representing the open uplands, open lowlands and woodlands. We also found comparable increases in an indicator of vegetation response to soil pH, Ellenberg R. Species characteristic of less acid soils tended to show more consistent increases in frequency across sites relative to species with a known tolerance for strongly acidic soils. These changes are, therefore, broadly consistent with a response to increases in soil solution pH observed for the majority of ECN sites that, in turn, are likely to be driven by large reductions in acid deposition in recent decades. Increases in species richness in certain habitat groupings could also be linked to increased soil moisture availability in drier lowland sites that are likely to have been influenced by a trend towards wetter summers in recent years, and possibly also to a reduction in soil nitrogen availability in some upland locations. Changes in site management are also likely to have influenced trends at certain sites, particularly with respect to agricultural practices. Our results are therefore indicative of widescale responses to major regional-scale changes in air pollution and recent weather patterns, modified by local management effects. The relative consistency of management of ECN sites over time is atypical of much of the wider countryside and it is therefore not appropriate to scale up these observations to infer national scale trends. Nevertheless the results provide an important insight into processes that may be operating nationally. It will now be necessary to test for the ubiquity of these changes using appropriate broader spatial scale survey data.     

Assessment of nitrogen flows into the Cuban landscape

The alteration of the nitrogen (N) cycle by human activities is widespread and has often resulted in increased flows of nitrogen to the marine environment. In this paper we have attempted to know the changes of N fluxes in Cuba by quantifying the N inputs to the landscape from (1) fertilizer applications, (2) atmospheric deposition, (3) biological nitrogen fixation and (4) net import of food and feeds. N-inputs to the country progressively increased until the end of the 20th century, reaching a peak during the 80s when low cost fertilizer imported from the former Soviet Union led to heavy rates of application. This rapid growth represented more than a 5-fold increase with respect to pristine values; higher than the two-fold global increase of anthropogenic N reported by Vitousek et al. (1997 Human alteration of the global nitrogen cycle: sources and consequences. Ecol. Appl. 7:737–750). Inorganic fertilizer was the largest single source of reactive N, followed by atmospheric deposition, biological fixation, and net imports of foods and feedstocks. Nitrogen inputs peaked in 1987 and data expressed on an area basis show that N flux to the Cuban landscape, in the 80s, was one of the highest reported in the literature. During the 90s, there was a dramatic drop in nitrogen inputs mainly associated to a decrease in the use of inorganic fertilizer. Other factors reducing nutrient inflows to Cuba, during the same period, were imports of foodstuff and livestock feeds, a decrease of nitrogen oxide emissions, and a decrease in the sugar cane crop area. Using an empirical relationship (Howarth et al. 1996 Regional nitrogen budgets and riverine N & O fluxes for the drainages to the North Atlantic Ocean: Natural and human influences. Biogeochemistry 35:75–139) we present a very preliminary estimate of N-inputs to coastal waters and discuss the consequences of these changes on the coastal zone.     

Global assessment of coral bleaching and required rates of adaptation under climate change

Elevated ocean temperatures can cause coral bleaching, the loss of colour from reef‐building corals because of a breakdown of the symbiosis with the dinoflagellate Symbiodinium. Recent studies have warned that global climate change could increase the frequency of coral bleaching and threaten the long‐term viability of coral reefs. These assertions are based on projecting the coarse output from atmosphere–ocean general circulation models (GCMs) to the local conditions around representative coral reefs. Here, we conduct the first comprehensive global assessment of coral bleaching under climate change by adapting the NOAA Coral Reef Watch bleaching prediction method to the output of a low‐ and high‐climate sensitivity GCM. First, we develop and test algorithms for predicting mass coral bleaching with GCM‐resolution sea surface temperatures for thousands of coral reefs, using a global coral reef map and 1985–2002 bleaching prediction data. We then use the algorithms to determine the frequency of coral bleaching and required thermal adaptation by corals and their endosymbionts under two different emissions scenarios. The results indicate that bleaching could become an annual or biannual event for the vast majority of the world's coral reefs in the next 30–50 years without an increase in thermal tolerance of 0.2–1.0°C per decade. The geographic variability in required thermal adaptation found in each model and emissions scenario suggests that coral reefs in some regions, like Micronesia and western Polynesia, may be particularly vulnerable to climate change. Advances in modelling and monitoring will refine the forecast for individual reefs, but this assessment concludes that the global prognosis is unlikely to change without an accelerated effort to stabilize atmospheric greenhouse gas concentrations.     

Using the output from global circulation models to predict changes in the distribution and abundance of cereal aphids in Canada: a mechanistic modeling approach

Climate change will alter the abundance and distribution of species. Predicting these shifts is a challenge for ecologists and essential information for the formation of public policy. Here, I use a mechanistic mathematical model of the interaction between grass growth physiology and aphid population dynamics, coupled with the climate change projections from the UK's Hadley Centre HadCM3 global circulation model (GCM) and Canada's Center for Climate Modeling and Analysis CGCM2 GCM to predict the changes in the abundance and distribution of summer cereal aphid populations in wheat-growing regions of Canada. When used with the HadCM3 projections, the model predicts a latitudinal shift northward in abundances but there is longitudinal variation as well. However, when used with the CGCM2 projections the model predicts that continental regions will see a decline while coastal regions will see an increase in summer cereal aphid populations. These effects are stronger under the higher emissions scenarios.     

Safety zones for a Sclerotinia sclerotiorum-based mycoherbicide: Accounting for regional and yearly variation in climate

Variation in the width of 'safety zones' for sheep and dairy pasture treated with a Sclerotinia sclerotiorum (Lib.) de Bary-based mycoherbicide was quantified using 10 years of climate data from each of five regions in New Zealand. Acceptable and risk-averse zones were defined as the maximum distances in any direction from a treated pasture where 'added:natural' ratios of air-borne S. sclerotiorum spores are 1:1 and 1:10, respectively. The 10-year mean 1:1 safety zone had zero width for sheep pasture at all locations, and was at most, 50 m wide for dairy pasture. The width of the 10-year mean 1:10 zone varied regionally from 314 to 443 m for sheep and from 175 to 280 m for dairy pasture, and the 90th percentile 1:10 zones were up to 41% wider. Linear relationships between safety zone width and mean wind speed were evident and these could be used to derive region-specific safety zones.     

荒漠生态系统对大气CO2浓度升高响应的干湿年差异

利用一个基于详细生理学过程的生态系统模型PALS-FT,通过模拟实验分析了美国亚利桑那州(Arizona)首府凤凰城(Phoenix)市西郊的Larreatridentata荒漠生态系统在干湿年份(1988-2002年)对大气CO2浓度升高响应的差别。结果表明,生态系统地上净初级生产力(ANPP)和土壤有机质年累积速率(SOM)均随大气CO2浓度升高而呈非线性(湿年)或线性(正常年和干年)增加;所有年份的土壤N含量(Nsoil)则呈非线性显著下降。ANPP与SOM的绝对变化量总是湿年大于正常年和干年,相对变化量则与所分析的CO2处理水平有关;Nsoil的绝对变化量和相对变化量均为湿年大于正常年和干年。不同功能型的植物ANPP对大气CO2浓度升高的绝对变化量均为湿年大于正常年和干年;相对变化量则因具体植物功能型而异,灌木和亚灌木为干年大于正常年和湿年,一年生C3和C4草本均为湿年大于正常年和干年。因此,无论是生态系统水平还是植物功能型(或物种)水平,荒漠生态系统对未来大气CO2浓度升高的响应都将受降水格局的显著影响。     

Tbx18 regulates development of the epicardium and coronary vessels

The epicardium and coronary vessels originate from progenitor cells in the proepicardium. Here we show that Tbx18, a T-box family member highly expressed in the proepicardium, controls critical early steps in coronary development. In Tbx18^−/− mouse embryos, both the epicardium and coronary vessels exhibit structural and functional defects. At E12.5, the Tbx18-deficient epicardium contains protrusions and cyst-like structures overlying a disorganized coronary vascular plexus that contains ectopic structures resembling blood islands. At E13.5, the left and right coronary stems form correctly in mutant hearts. However, analysis of PECAM-1 whole mount immunostaining, distribution of SM22α^lacZ/+ activity, and analysis of coronary vascular casts suggest that defective vascular plexus remodeling produces a compromised arterial network at birth consisting of fewer distributing conduit arteries with smaller lumens and a reduced capacity to conduct blood flow. Gene expression profiles of Tbx18^−/− hearts at E12.5 reveal altered expression of 79 genes that are associated with development of the vascular system including sonic hedgehog signaling components patched and smoothened, VEGF-A, angiopoietin-1, endoglin, and Wnt factors compared to wild type hearts. Thus, formation of coronary vasculature is responsive to Tbx18-dependent gene targets in the epicardium, and a poorly structured network of coronary conduit vessels is formed in Tbx18 null hearts due to defects in epicardial cell signaling and fate during heart development. Lastly, we demonstrate that Tbx18 possesses a SRF/CArG box dependent repressor activity capable of inhibiting progenitor cell differentiation into smooth muscle cells, suggesting a potential function of Tbx18 in maintaining the progenitor status of epicardial-derived cells.     

Ocular blood flow decreases during passive heat stress in resting humans

Background

Heat stress induces various physiological changes and so could influence ocular circulation. This study examined the effect of heat stress on ocular blood flow.

Findings

Ocular blood flow, end-tidal carbon dioxide (P_ETCO₂) and blood pressure were measured for 12 healthy subjects wearing water-perfused tube-lined suits under two conditions of water circulation: (1) at 35°C (normothermia) for 30 min and (2) at 50°C for 90 min (passive heat stress). The blood-flow velocities in the superior temporal retinal arteriole (STRA), superior nasal retinal arteriole (SNRA), and the retinal and choroidal vessels (RCV) were measured using laser-speckle flowgraphy. Blood flow in the STRA and SNRA was calculated from the integral of a cross-sectional map of blood velocity. P_ETCO₂ was clamped at the normothermia level by adding 5% CO₂ to the inspired gas. Passive heat stress had no effect on the subjects’ blood pressures. The blood-flow velocity in the RCV was significantly lower after 30, 60 and 90 min of passive heat stress than the normothermic level, with a peak decrease of 18 ± 3% (mean ± SE) at 90 min. Blood flow in the STRA and SNRA decreased significantly after 90 min of passive heat stress conditions, with peak decreases of 14 ± 3% and 14 ± 4%, respectively.

Conclusion

The findings of this study suggest that passive heat stress decreases ocular blood flow irrespective of the blood pressure or arterial partial pressure of CO₂.