Biology of the bamboo Chusquea culeou (Poaceae: Bambusoideae) in southern Argentina

Over a period of 7 years the biology and phenotypic variability of Chusquea culeou were studied at 5 locations in cool temperate forests of southern Argentina. Excavated rhizomes had an average of 1.1 successful rhizome buds, and an average of 2.1 years elapsed between successive generations of rhizomes. Rhizome buds usually develop within the first four years after a rhizome forms. Height, volume and weight of a culm can be calculated from its diameter 1 m above the ground. Culm size, length of foliage leaf blades, and pattern of secondary branching differed among study sites. Dead culms were numerous and commonly remained erect for more than 7 years after dying. New culm shoots appear in spring and reach full size within a few months. Shoots can grow more than 9 cm/day. Less than half of the shoots survived a year; most were killed by moth larvae. Multiple primary branch buds emerge through the culm leaf sheaths in the second spring. The mean number of branch buds at mid-culm nodes varied between 34.8 and 81.5, and the mean number of primary branches was between 22.8 and 40.8. Number and length of branches, and number and length of foliage leaf blades at each node is related to the position of the node on a culm. Most branches grow about 3 cm and produce 1 to 3 foliage leaves annually. Foliage leaf blades generally live 2 years or more; few survive 6 years. Relative lengths of foliage leaf blades and their spacing along a branch permit recognition of annual cohorts.Both gregarious and sporadic flowering have been reported, and every year a few isolated plants flower and die. Length of the life cycle is unknown. Seedlings require up to 15 years to produce culms of mature size. Foliage branches may live more than 23 years, and culms may survive 33 years. Extensive loss of new shoots to predation suggests that gregarious flowering may be driven by a need to escape parasitism. C. culeou clumps expand slowly. Average annual rate of increase of the number of live culms in a clump was 4.6%. Methods of seed dispersal are undocumented. A dense stand of Chusquea culeou had an estimated phytomass of 179 tons/hectare (dry weight), 28% of which was underground. Net annual production was about 16 t/ha dry weight.     

Feeding behaviour of Cerastoderma edule in a turbid environment: physiological adaptations and derived benefit

Resuspension of bottom sediments by wind andtide-driven currents often occur in shallow waters,coastal embayments and estuaries. These processes maylead to dramatic variations in the concentration andorganic richness of suspended particle assemblages.Since resuspended matter is mainly inorganic,decreasing organic contents are usually associatedwith higher seston loads.Under this environmental context the feeding behaviourof bivalves shows a wide degree of plasticity, whichhas been interpreted as having high adaptive value. Inorder to evaluate benefits derived from thisbehaviour, we have used functional relationshipsobtained in previous studies, relating feedingparameters to characteristics of suspended food, topredict the effect that different feeding responseswould have exerted. In cockles, main processesdetermining energy acquisition are feeding rates andpreingestive food selection. Thus, the procedurefollowed in the present work consisted of simulatingrates of food absorption under alternative feedingbehaviours characterised by: (a) no preferentialingestion of filtered organic matter and (b) maintenance ofconstant clearance rates. In theabsence of selection of organic matter at thepreingestive level, ingestion rate of organics (OIR)would decline with increasing seston loads to 30% ofvalues predicted by functions fitted to experimentaldata; difference in absorption rate (AR) would be evengreater, falling to 10%, due to the strong effectthat the organic content of ingested matter exerts onabsorption efficiency. On the other hand, had theclearance rate (CR) kept constant despite theincreasing seston load, OIR and AR would have fallento values respectively 30% and 49% lower than actualvalues.From these results it is concluded that the ability ofsorting particles before ingestion and the capabilityof adjusting clearance rate are key elements in thefeeding behaviour that enable cockles to be welladapted to cope with changes in the water columncaused by resuspension events.     

Prevalence and upper limit of cardiac hypertrophy in professional cyclists

The term athlete's heart refers to an increased left ventricular mass. Few studies have assessed the prevalence and normal upper limit of cardiac hypertrophy in highly trained cyclists and this was the aim of this study. A group of 40 professional road cyclists [mean age 26 (SD 3) years] who had participated in European competitions for 3–10 years, were evaluated at the beginning of the 1992–93 season. Evaluation included a clinical history and physical examination, one and two-dimensional echocardiography, 12-lead resting electrocardiogram and a graded exercise test. Determination of the left ventricular mass index (LVMI) was performed using Devereux's formula with correction for the body surface area. Systolic and diastolic blood pressure were measured at rest and at peak exercise. Of the group 23 cyclists (58%) presented a LVMI greater than 130 g · m^–2, 21 cyclists presented a diastolic ventricular thickness equal to or greater than 13 mm, with a superior limit of 19 mm; 3 cyclists presented asymmetrical septum hypertrophy; and the relationship between posterior wall and left ventricular diastolic radius was equal to or greater than 0.45 in 14 cases (35%). Electrocardiographic abnormalities of ST-T segment were seen in only 1 subject. No correlation was found between the degree of ventricular hypertrophy and arterial blood pressure. We concluded that these professional cyclists showed a high prevalence of cardiac hypertrophy (58%). The distribution of this hypertrophy was concentric in 20/33 and asymmetric in 3/23 of the subjects with left ventricular hypertrophy. The electrocardiograms were normal in 98% of the subjects.     

The blood-brain barrier: an alternative hypothesis

Brain blood vessels, unlike most vessels elsewhere in the body, exhibit a blood-brain barrier (BBB) to certain substances, e.g. trypan blue. Under some circumstances this barrier is no longer effective and the permeability of the vessels increases. Although capillarization is much less in the brain than in many other organs, e.g. heart muscle, total cerebral blood flow per minute is enormous. Consequently, to accommodate a large blood volume with a limited capillary bed, the velocity of blood through brain vessels must be extremely fast. The hypothesis presented in this paper is that this rapid flow results in a low or negative pressure on the endothelium, and plasma and trypan blue are prevented from passing through the wall. The tight junctions of cerebral endothelial cells may be able to withstand only a limited amount of pressure on their luminal surface. If the velocity of blood in brain capillaries decreases, pressure on the endothelium should increase, and brain vessels, like blood vessels elsewhere in the body, become permeable to vital dyes. Other conditions also increase capillary permeability, e.g. acute arterial hypertension or venous congestion. Although brain vessels can adapt to a moderate, gradual change in systemic pressure, when a significant rise in cerebral arterial pressure is abrupt, the compensatory changes in the postcapillary venous bed may be inadequate and consequently intracapillary pressure and vascular permeability are increased. Venous congestion increases intracapillary pressure by restricting capillary outflow as well as by reducing velocity through capillary beds. Under such conditions increased capillary permeability may be indicated by cerebral edema, and even, on occasion, by petechial hemorrhages. In short, if the flow is fast and unimpeded the BBB will be effective; if the velocity decreases, or intracapillary pressure increases for whatever reason, the permeability of the brain endothelium will be abnormally increased.     

A brief comparative study of four disposable bubble oxygenators

Four widely used bubble oxygenators-the Optiflo I, the Bentley Q 200 A, the Harvey 200, and the Shiley 100 A-were tested and compared in 182 patients undergoing cardiac valve surgery. Fifty-six cases were performed with normothermia and 126 cases incorporated mild hypothermia (28-30 degrees C). There was no significant difference in the average age of the patients (51 yrs) or the perfusion time (60 min). All components of the extracorporeal circuit were identical, and anesthetic regimens and surgical techniques were also similar. In this study, the Shiley 100 A oxygenator was found to be the most suitable for cases requiring mild hypothermia and was generally considered to be the oxygenator of choice.     

SARS-CoV-2 seropositivity and COVID-19 among 5 years-old Amazonian children and their association with poverty and food insecurity

BackgroundThe epidemiology of childhood SARS-CoV-2 infection and COVID-19-related illness remains little studied in high-transmission tropical settings, partly due to the less severe clinical manifestations typically developed by children and the limited availability of diagnostic tests. To address this knowledge gap, we investigate the prevalence and predictors of SARS-CoV-2 infection (either symptomatic or not) and disease in 5 years-old Amazonian children.Methodology/Principal findingsWe retrospectively estimated SARS-CoV-2 attack rates and the proportion of infections leading to COVID-19-related illness among 660 participants in a population-based birth cohort study in the Juruá Valley, Amazonian Brazil. Children were physically examined, tested for SARS-CoV-2 IgG and IgM antibodies, and had a comprehensive health questionnaire administered during a follow-up visit at the age of 5 years carried out in January or June-July 2021. We found serological evidence of past SARS-CoV-2 infection in 297 (45.0%; 95% confidence interval [CI], 41.2–48.9%) of 660 cohort participants, but only 15 (5.1%; 95% CI, 2.9–8.2%) seropositive children had a prior medical diagnosis of COVID-19 reported by their mothers or guardians. The period prevalence of clinically apparent COVID-19, defined as the presence of specific antibodies plus one or more clinical symptoms suggestive of COVID-19 (cough, shortness of breath, and loss of taste or smell) reported by their mothers or guardians since the pandemic onset, was estimated at 7.3% (95% CI, 5.4–9.5%). Importantly, children from the poorest households and those with less educated mothers were significantly more likely to be seropositive, after controlling for potential confounders by mixed-effects multiple Poisson regression analysis. Likewise, the period prevalence of COVID-19 was 1.8-fold (95%, CI 1.2–2.6-fold) higher among cohort participants exposed to food insecurity and 3.0-fold (95% CI, 2.8–3.5-fold) higher among those born to non-White mothers. Finally, children exposed to household and family contacts who had COVID-19 were at an increased risk of being SARS-CoV-2 seropositive and–even more markedly–of having had clinically apparent COVID-19 by the age of 5 years.Conclusions/SignificanceChildhood SARS-CoV-2 infection and COVID-19-associated illness are substantially underdiagnosed and underreported in the Amazon. Children in the most socioeconomically vulnerable households are disproportionately affected by SARS-CoV-2 infection and disease.     

Relationships between biological soil crusts,bacterial diversity and abundance,and ecosystem functioning: Insights from a semi‐arid Mediterranean environment

Questions: To what degree do biological soil crusts (BSCs), which are regulators of the soil surface boundary, influence associated microbial communities? Are these associations important to ecosystem functioning in a Mediterranean semi‐arid environment? Location: Gypsum outcrops near Belmonte del Tajo, Central Spain. Methods: We sampled a total of 45 (50 cm × 50 cm) plots, where we estimated the cover of every lichen and BSC‐forming lichen species. We also collected soil samples to estimate bacterial species richness and abundance, and to assess different surrogates of ecosystem functioning. We used path analysis to evaluate the relationships between the richness/abundance of above‐ and below‐ground species and ecosystem functioning. Results: We found that the greatest direct effect upon the ecosystem function matrix was that of the biological soil crust (BSC) richness matrix. A few bacterial species were sensitive to the lichen community, with a disproportionate effect of Collema crispum and Toninia sedifolia compared to their low abundance and frequency. The lichens Fulgensia subbracteata and Toninia spp. also had negative effects on bacteria, while Diploschistes diacapsis consistently affected sensitive bacteria, sometimes positively. Despite these results, very few of the BSC effects on ecosystem function could be ascribed to changes within the bacterial community. Conclusion: Our results suggest the primary importance of the richness of BSC‐forming lichens as drivers of small‐scale changes in ecosystem functioning. This study provides valuable insights on semi‐arid ecosystems where plant cover is spatially discontinuous and ecosystem function in plant interspaces is regulated largely by BSCs.