The oxygen delivery response to acute hypoxia during incremental knee extension exercise differs in active and trained males

Background

It is well known that hypoxic exercise in healthy individuals increases limb blood flow, leg oxygen extraction and limb vascular conductance during knee extension exercise. However, the effect of hypoxia on cardiac output, and total vascular conductance is less clear. Furthermore, the oxygen delivery response to hypoxic exercise in well trained individuals is not well known. Therefore our aim was to determine the cardiac output (Doppler echocardiography), vascular conductance, limb blood flow (Doppler echocardiography) and muscle oxygenation response during hypoxic knee extension in normally active and endurance-trained males.

Methods

Ten normally active and nine endurance-trained males (VO_2max = 46.1 and 65.5 mL/kg/min, respectively) performed 2 leg knee extension at 25, 50, 75 and 100% of their maximum intensity in both normoxic and hypoxic conditions (FIO₂ = 15%; randomized order). Results were analyzed with a 2-way mixed model ANOVA (group × intensity).

Results

The main finding was that in normally active individuals hypoxic sub-maximal exercise (25 – 75% of maximum intensity) brought about a 3 fold increase in limb blood flow but decreased stroke volume compared to normoxia. In the trained group there were no significant changes in stroke volume, cardiac output and limb blood flow at sub-maximal intensities (compared to normoxia). During maximal intensity hypoxic exercise limb blood flow increased approximately 300 mL/min compared to maximal intensity normoxic exercise.

Conclusion

Cardiorespiratory fitness likely influences the oxygen delivery response to hypoxic exercise both at a systemic and limb level. The increase in limb blood flow during maximal exercise in hypoxia (both active and trained individuals) suggests a hypoxic stimulus that is not present in normoxic conditions.

     

Development and field application of a molecular probe for the primary pathogen of the coral disease white plague type II

One of the current problems in the field of coral disease research is that of tracking coral pathogens in the natural environment. A promising method to do this is by use of pathogen-specific molecular probes. However, this approach has been little used to date. We constructed, and validated in the laboratory, a fluorochrome-labeled molecular probe specific to Aurantimonas coralicida, the bacterial pathogen of the Caribbean coral disease white plague type II (WPIl). We then used the probe to test field samples of diseased coral tissue for the presence of this pathogen. Probe design was based on a unique subset (25 nucleotides) of the complete l6S rRNA gene sequence derived from a pure culture of the pathogen. The pathogen-specific probe was labeled with the fluorochrome GreenStar* FITC (fluorescein isothiocyanate, GeneDetect Ltd, New Zealand). As a control, we used the universal eubacterial probe EUB 338, labeled with a different fluorochrome (TRITC, tetra-methylrhodamine isothiocyanate). Both probes were applied to laboratory samples of pure cultures of bacteria, and field samples collected from the surface of the disease line of corals exhibiting signs of white plague (types I and II), healthy controls, and corals with an uncharacterized disease ("patchy necrosis"). All samples were analyzed using fluorescence in situ hybridization (FISH). We have determined that the probe is specific to our laboratory culture of the coral pathogen, and does not react with other bacterial species (the eubacterial probe does). The WPII pathogen was detected in association with diseased coral samples collected from coral colonies on reefs of the Bahamas (n= 9 samples) exhibiting signs of both WPI and WPII. Diseased (and healthy) tissue samples (n- 4) from corals exhibiting signs of "patchy necrosis" were also assayed. In this case the results were negative, indicating that the same pathogen is not involved in the two diseases. Incorporation and use of pathogen-specific probes can significantly expand our knowledge of the etiology of coral diseases.     

Low incidence of polyploids and high uniformity of karyotypes displayed by Delphinium (Ranunculaceae) in the Hengduan Mountains region of south‐west China

The chromosome numbers and morphology in 92 populations belonging to 49 species and three varieties in the genus Delphinium L. (Ranunculaceae), mostly from the Hengduan Mountains region of south‐west China, were studied. Forty seven species and three varieties were diploid, with 2n = 16, one species was tetraploid, with 2n = 32, and one species had diploid and tetraploid cytotypes. Three species had B chromosomes, representing the first time the occurrence of B chromosomes has been reported in the genus. The karyotypes of all the diploid species were quite uniform, commonly bimodal, and usually consisted of one pair of large median‐centromeric (m), one pair of large submedian‐centromeric (sm), five pairs of medium‐sized subterminal‐centromeric (st), and one pair of smaller sm (rarely st) chromosomes. The low incidence of polyploids in Delphinium from the Hengduan Mountains region indicates that polyploidy has played a minor role in the speciation of this highly diversified genus in the region. © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society, 2008, 158 , 172–188.     

Relative accuracy of spatial predictive models for lynx Lynx canadensis derived using logistic regression-AIC,multiple criteria evaluation and Bayesian approaches

We compared probability surfaces derived using one set of environmental variables in three Geographic Information Systems (GIS) -based approaches: logistic regression and Akaike's Information Criterion (AIC),Multiple Criteria Evaluation (MCE),and Bayesian Analysis (specifically Dempster-Shafer theory). We used lynx Lynx canadensis as our focal species,and developed our environment relationship model using track data collected in Banff National Park,Alberta,Canada,during winters from 1997 to 2000. The accuracy of the three spatial models were compared using a contingency table method. We determined the percentage of cases in which both presence and absence points were correctly classified (overall accuracy),the failure to predict a species where it occurred (omission error) and the prediction of presence where there was absence (commission error). Our overall accuracy showed the logistic regression approach was the most accurate (74.51% ). The multiple criteria evaluation was intermediate (39.22%),while the Dempster-Shafer (D-S) theory model was the poorest (29.90%). However,omission and commission error tell us a different story: logistic regression had the lowest commission error,while D-S theory produced the lowest omission error. Our results provide evidence that habitat modellers should evaluate all three error measures when ascribing confidence in their model. We suggest that for our study area at least,the logistic regression model is optimal. However,where sample size is small or the species is very rare,it may also be useful to explore and/or use a more ecologically cautious modelling approach (e.g. Dempster-Shafer) that would over-predict,protect more sites,and thereby minimize the risk of missing critical habitat in conservation plans.     

Temporal variability in the spatial and environmental determinants of functional metacommunity organization – stream fish in a human‐modified landscape

1. Quantifying the relative importance of environmental filtering versus regional spatial structuring has become an intensively studied area in the context of metacommunity ecology. However, most studies have evaluated the role of environmental and spatial processes using taxonomic data sets of single snapshot surveys. 2. Here, we examined temporal changes in patterns and possible processes behind the functional metacommunity organization of stream fishes in a human‐modified landscape. Specifically, we (i) studied general changes in the functional composition of fish assemblages among 40 wadeable stream sites during a 3‐year study period in the catchment area of Lake Balaton, Hungary, (ii) quantified the relative importance of spatial and environmental factors as determinants of metacommunity structure and (iii) examined temporal variability in the relative role of spatial and environmental processes for this metacommunity. 3. Partial triadic analysis showed that assemblages could be effectively ordered along a functional gradient from invertebrate consuming species dominated by the opportunistic life‐history strategy, to assemblages with a diverse array of functional attributes. The analysis also revealed that functional fish assemblage structure was moderately stable among the sites between the sampling periods. 4. Despite moderate stability, variance partitioning using redundancy analyses (RDA) showed considerable temporal variability in the contribution of environmental and spatial factors to this pattern. The analyses also showed that environmental variables were, in general, more important than spatial ones in determining metacommunity structure. Of these, natural environmental variables (e.g. altitude, velocity) proved to be more influential than human‐related effects (e.g. pond area, % inhabited area above the site, nutrient enrichment), even in this landscape with relatively low variation in altitude and stream size. 5. Pond area was, however, the most important human stressor variable that was positively associated with the abundance of non‐native species with diverse functional attributes. The temporal variability in the relative importance of environmental and spatial factors was probably shaped by the release of non‐native fish from fish ponds to the stream system during flood events. 6. To conclude, both spatial processes and environmental control shape the functional metacommunity organization of stream fish assemblages in human‐modified landscapes, but their importance can vary in time. We argue, therefore, that metacommunity studies should better consider temporal variability in the ecological mechanisms (e.g. dispersal limitation, species sorting) that determine the dynamics of landscape‐level community organization.     

Pulse Decomposition Analysis of the digital arterial pulse during hemorrhage simulation

Background

Markers of temporal changes in central blood volume are required to non-invasively detect hemorrhage and the onset of hemorrhagic shock. Recent work suggests that pulse pressure may be such a marker. A new approach to tracking blood pressure, and pulse pressure specifically is presented that is based on a new form of pulse pressure wave analysis called Pulse Decomposition Analysis (PDA). The premise of the PDA model is that the peripheral arterial pressure pulse is a superposition of five individual component pressure pulses, the first of which is due to the left ventricular ejection from the heart while the remaining component pressure pulses are reflections and re-reflections that originate from only two reflection sites within the central arteries. The hypothesis examined here is that the PDA parameter T13, the timing delay between the first and third component pulses, correlates with pulse pressure. T13 was monitored along with blood pressure, as determined by an automatic cuff and another continuous blood pressure monitor, during the course of lower body negative pressure (LBNP) sessions involving four stages, -15 mmHg, -30 mmHg, -45 mmHg, and -60 mmHg, in fifteen subjects (average age: 24.4 years, SD: 3.0 years; average height: 168.6 cm, SD: 8.0 cm; average weight: 64.0 kg, SD: 9.1 kg).

Results

Statistically significant correlations between T13 and pulse pressure as well as the ability of T13 to resolve the effects of different LBNP stages were established. Experimental T13 values were compared with predictions of the PDA model. These interventions resulted in pulse pressure changes of up to 7.8 mmHg (SE = 3.49 mmHg) as determined by the automatic cuff. Corresponding changes in T13 were a shortening by -72 milliseconds (SE = 4.17 milliseconds). In contrast to the other two methodologies, T13 was able to resolve the effects of the two least negative pressure stages with significance set at p < 0.01.

Conclusions

The agreement of observations and measurements provides a preliminary validation of the PDA model regarding the origin of the arterial pressure pulse reflections. The proposed physical picture of the PDA model is attractive because it identifies the contributions of distinct reflecting arterial tree components to the peripheral pressure pulse envelope. Since the importance of arterial pressure reflections to cardiovascular health is well known, the PDA pulse analysis could provide, beyond the tracking of blood pressure, an assessment tool of those reflections as well as the health of the sites that give rise to them.     

The presence of the cyanobacterial toxin microcystin in black band disease of corals

Black band disease (BBD) is a migrating, cyanobacterial dominated, sulfide-rich microbial mat that moves across coral colonies lysing coral tissue. While it is known that BBD sulfate-reducing bacteria contribute to BBD pathogenicity by production of sulfide, additional mechanisms of toxicity may be involved. Using HPLC/MS, the cyanotoxin microcystin was detected in 22 field samples of BBD collected from five coral species on nine reefs of the wider Caribbean (Florida Keys and Bahamas). Two cyanobacterial cultures isolated from BBD, Geitlerinema and Leptolyngbya sp. contained microcystin based on HPLC/MS, with toxic activity confirmed using the protein phosphatase inhibition assay. The gene mcyA from the microcystin synthesis complex was detected in two field samples and from both BBD cyanobacterial cultures. Microcystin was not detected in six BBD samples from a different area of the Caribbean (St Croix, USVI) and the Philippines, suggesting regional specificity for BBD microcystin. This is the first report of the presence of microcystin in a coral disease.     

Black Band Disease Microbial Community Variation on Corals in Three Regions of the Wider Caribbean

Black band disease (BBD) is a pathogenic consortium of microorganisms that primarily affects massive framework-building scleractinian corals on reefs worldwide. There has been considerable debate concerning the microbial community composition of BBD. The aim of this study was to utilize microbial profiling to assess overall patterns of variation in the BBD bacterial community with respect to geographic location, host coral species, time, and nutrient regime. Length heterogeneity polymerase chain reaction (LH-PCR) was employed to differentiate BBD communities based on the natural variation in the sequence lengths within hypervariable domains of the 16S rRNA gene. Analysis of LH-PCR profiles of 97 BBD samples using multivariate ordination methods and analysis of similarity revealed significant clustering with respect to geographic region when comparing BBD sampled from reefs near Lee Stocking Island in the Bahamas’ Exuma Chain, the Northern Florida Keys (NFK), and St. John in the US Virgin Islands. There was much variability in BBD community composition on a regional basis, between sites in the NFK, and in terms of coral host species. The observed differences among BBD microbial community profiles were driven primarily by variation in relative abundance of 313–316-bp amplicons, which correspond to cyanobacteria and α-proteobacteria. The results obtained in this study support previous reports of intrinsic variability and complexity of the BBD microbial community but also suggest that this variability has biogeographic patterns.