Does low daily energy expenditure drive low metabolic capacity in the tropical robin, Turdus grayi?

Temperate and tropical birds possess divergent life history strategies. Physiological parameters including energy metabolism correlate with the life history such that tropical species with a slower ‘pace of life’ have lower resting and maximal metabolic rates than temperate congeners. To better understand the physiological mechanisms underlying these differences, we investigated the relationship of metabolic capacity, muscle oxidative capacity and activity patterns to variation in life history patterns in American robins (Turdus migratorius), while resident in central North America and Clay-colored robins (Turdus grayi) resident in Panama. We measured summit metabolism $ \left( {\dot{V}{\text{O}_{2\text{summit}}}} \right) $ in birds from both tropical and temperate habitats and found that the temperate robins have a 60 % higher metabolic capacity. We also measured the field metabolic rate (FMR) of free-living birds using heart rate (HR) telemetry and found that temperate robins’ daily energy expenditure was also 60 % higher. Thus, $\dot{V}{\text{O}_{2\text{summit}}} $ and FMR both reflect life history differences between the species. Further, both species operate at a nearly identical ~50 % of their thermogenic capacity throughout a given day. As a potential mechanism to explain differences in activity and metabolic capacity, we ask whether oxidative properties of flight muscle are altered in accordance with life history variation and found minimal differences in oxidative capacity of skeletal muscle. These data demonstrate a close relationship between thermogenic capacity and daily activity in free-living birds. Further, they suggest that the slow pace of life in tropical birds may be related to the maintenance of low activity rather than functional capacity of the muscle tissue.     

Low blood pressure,low mood?

OBJECTIVE--To determine whether a set of physical symptoms is associated with low blood pressure and to investigate the possible role of psychological factors in their occurrence. DESIGN--Analysis of data collected by questionnaire and physical screening from the first phase of the Whitehall II study, a cohort study of an employed population. SETTING--23 civil service departments in London. SUBJECTS--10,314 male and female London based civil servants aged between 35 and 55. MAIN OUTCOME MEASURES--Symptoms of dizziness-giddiness and unexplained tiredness; psychological functioning as measured by the 30 item general health questionnaire in which the response "no more than usual" to an item about disease was scored as indicating chronic illness. RESULTS--Dizziness-giddiness in men and unexplained tiredness in both men and women were significantly related to low systolic blood pressure. There was a highly significant inverse relation between general health questionnaire score and systolic blood pressure for both men and women, which persisted after controlling for potentially confounding variables, including age, body mass index, drug treatment, physical illness, and exercise. This association of low blood pressure with physical symptoms was no longer significant when general health questionnaire score was controlled for. CONCLUSIONS--There seems a strong relation between low systolic blood pressure and minor psychological dysfunction. Associated physical symptoms seem to be secondary to the primary disturbance in mental state.     

A new model for very low density lipoprotein metabolism—Nomenclature for very low density lipoprotein derivatives

A new model for the catabolism of very low density lipoprotein will be proposed following a brief discussion of the relevant information about its metabolism. This model is based on the assumption that each very low density lipoprotein derivative has a distinct structural feature which determines its biological fate. Since this unique determinant may reside in only a small portion of the particles, such as apoprotein, the different very low density lipoprotein derivatives may possess similar or even identical electrophoretic mobility or hydrated density. For this reason, we propose that very low density lipoprotein derivatives be defined according to their putative position in the metabolic pathways rather than according to their hydrated density or their electrophoretic behavior. Thus it is recommended that biochemical separation methods based on principles other than electrophoretic mobility or hydrated density be used to isolate, purify and define very low density lipoprotein derivatives. The position that a lipoprotein particle occupies in the catabolic pathways should be determined by its ability to interact with liver cells or its ability to become converted to low density lipoprotein. This new nomenclature would eliminate unnecessary confusion and stimulate more research toward elucidating the unique structural feature of each very low density lipoprotein derivative.     

The conservative low‐phosphorus niche in Proteaceae

Plant and Soil - Intercropping cereals with legumes may achieve high crop yields at reduced input levels. Several studies have indicated that intercropping increases phosphorus use efficiency but...     

Do low oxygen environments facilitate marine invasions? Relative tolerance of native and invasive species to low oxygen conditions

Biological invasions are one of the biggest threats to global biodiversity. Marine artificial structures are proliferating worldwide and provide a haven for marine invasive species. Such structures disrupt local hydrodynamics, which can lead to the formation of oxygen‐depleted microsites. The extent to which native fauna can cope with such low oxygen conditions, and whether invasive species, long associated with artificial structures in flow‐restricted habitats, have adapted to these conditions remains unclear. We measured water flow and oxygen availability in marinas and piers at the scales relevant to sessile marine invertebrates (mm). We then measured the capacity of invasive and native marine invertebrates to maintain metabolic rates under decreasing levels of oxygen using standard laboratory assays. We found that marinas reduce water flow relative to piers, and that local oxygen levels can be zero in low flow conditions. We also found that for species with erect growth forms, invasive species can tolerate much lower levels of oxygen relative to native species. Integrating the field and laboratory data showed that up to 30% of available microhabitats within low flow environments are physiologically stressful for native species, while only 18% of the same habitat is physiologically stressful for invasive species. These results suggest that invasive species have adapted to low oxygen habitats associated with manmade habitats, and artificial structures may be creating niche opportunities for invasive species.     

Numbats and aardwolves—how low is low? A re-affirmation of the need for statistical rigour in evaluating regression predictions

Many comparative physiological studies aim to determine if a particular species differs from a prediction based on a linear allometric regression for other species. However, the judgment as to whether the species in question conforms to this allometric relationship is often not based on any formal statistical analysis. An appropriate statistical method is to compare the new species’ value with the 95% confidence limits for predicting an additional datum from the relationship for the other species. We examine the basal metabolic rate (BMR) of the termitivorous numbat (Myrmecobius fasciatus) and aardwolf (Proteles cristatus) to demonstrate the use of the 95% prediction limits to determine statistically if they have a lower-than-expected BMR compared to related species. The numbat’s BMR was 83.6% of expected from mass, but fell inside the 95% prediction limits for a further datum; a BMR < 72.5% of predicted was required to fall below the one-tail 95% prediction limits. The aardwolf had a BMR that was only 74.2% of predicted from the allometric equation, but it also fell well within the 95% prediction limits; a BMR of only 41.8% of predicted was necessary to fall below the one-tail 95% prediction limits. We conclude that a formal statistical approach is essential, although it is difficult to demonstrate that a single species statistically differs from a regression relationship for other species.     

Are low cholesterol values associated with excess mortality?

The relation between cholesterol concentration and mortality was studied prospectively over 17 years in 630 New Zealand Maoris aged 25-74. The dead or alive state of each person was determined in 1981. The causes of death were divided into three categories: cancer, cardiovascular disease, and "other." Using univariate and both linear and non-linear multivariate methods of analysis for survivorship data, significant inverse relations with serum cholesterol were found for total mortality in women, for mortality from cancer in men and women, and for other causes of mortality in both men and women. The inverse and non-linear association with total mortality in women remained significant when deaths in the first five years of follow up were excluded. This suggests that the association was not explained by undetected illness causing low cholesterol concentrations at the time of initial examination.     

Why is liana abundance low in semiarid climates?

Lianas are abundant in seasonal tropical forests, where they avoid seasonal water stress presumably by accessing deep‐soil water reserves. Although lianas are favoured in seasonal environments, their occurrence and abundance are low in semiarid environments. We hypothesized that lianas do not tolerate the great water shortage in the soil and air characteristic of semiarid environments, which would increase the risk of embolism. We compared the rooting depth of coarse roots, leaf dynamics, leaf water potential (ψ_leaf), embolism resistance (P₅₀) and lethal levels of embolism (P₈₈) between congeneric lianas that occur with different abundances in two semiarid sites differing in soil characteristics and vapour pressure deficit in the air (VPD_air). Regardless of soil texture and depth, water availability was restricted to the rainy season. All liana species were drought deciduous and had superficial coarse roots (not deeper than 35 cm). P₅₀ varied from ?1.8 to ?2.49 MPa, and all species operated under narrow safety margins against catastrophic (P₅₀) and irreversible hydraulic failure (P₈₈), even during the rainy season. In short, lianas that occur in semiarid environments have lower resistance to cavitation and limit carbon fixation to the rainy season because of leaf fall in the early dry season. We suggest that leaf shedding and shallow roots impairing carbon gain and growth in the dry season may explain why liana abundance is lower in semiarid than in other seasonally dry environments.     

Assessing genetic diversity in clonal organisms: low diversity or low resolution? Combining power and cost efficiency in selecting markers

The increasing use of molecular tools to study populations of clonal organisms leads us to question whether the low polymorphism found in many studies reflects limited genetic diversity in populations or the limitations of the markers used. Here we used microsatellite datasets for two sea grass species to provide a combinatory statistic, combined with a likelihood approach to estimate the probability of identical multilocus genotypes (MLGs) to be shared by distinct individuals, in order to ascertain the efficiency of the markers used and to optimize cost-efficiently the choice of markers to use for deriving unbiased estimates of genetic diversity. These results strongly indicate that conclusions from studies on clonal organisms derived using markers showing low polymorphism, including microsatellites, should be reassessed using appropriate polymorphic markers.     

Why are aggregates destroyed in low intensity fire?

Soil structure is often severely affected during high intensity burning, while low intensity prescribed burning has often been thought to have a low or neutral effect on soil aggregation. In this issue of Plant and Soil, (Albalasmeh et al. 2012) report a novel mechanism of aggregate disruption during low intensity burning that may explain some contradictory results reported in previous studies. Albalasmeh et al. (2012) suggest that during rapid heating of moist soil aggregates, intra-aggregate water is vaporized and the increased pressure causes rupture of the internal bonds and leads to aggregate breakdown. This mechanism can be compared to the aggregate breakdown due to slaking, when dry aggregates are suddenly wetted or submerged in water. Identification of the reasons for the aggregate disruption at low temperatures is important for choosing optimal soil and weather conditions for prescribed fires.     

Motion processing: how low can you go?

Neurons at early stages in the visual system can only 'view' small parts of the visual world, impeding their ability to determine correctly an object's motion direction. New studies suggest that this 'aperture problem' is already solved by special neurons at the first stage of motion detection in primary visual cortex.     

Debate: "How low should LDL cholesterol be lowered?" Viewpoint: "It doesn't need to be very low"

The importance of low-density lipoprotein (LDL) control in the management of patients at high risk of cardiovascular events is unquestionable. The major statin trials have shown that the benefits of LDL lowering extend throughout the range of risk and the range of serum cholesterol, and have indicated that the protective effects of the intervention are mostly related to the baseline risk. Statin therapy is, for this reason, currently seen as an anti-atherogenic approach for the majority of high risk individuals and possibly all coronary heart disease patients. This debate is not about the value of statin therapy or the importance of LDL reduction, but about the goals to be set once we decide that LDL cholesterol must be reduced. With the National Cholesterol Education Program (NCEP) guidelines representing a solid middle ground, the two viewpoints in this debate try to argue, on one hand, that the LDL goals should be substantially lower than our current standards or, on the other, that a specific on-treatment LDL value may not be the most important goal to pursue. We defend the latter position by presenting the case that the most effective LDL intervention in high risk patients is to achieve a reduction of at least 30%. This strategy complies with the NCEP guidelines, as most of the high risk patients treated with an average dose of an average statin would experience a 30-40% LDL reduction that would put on-treatment LDL levels safely below goal. Our position differs from both the guidelines and the proponents of more aggressive LDL goals in the management of the two extremes of the cholesterol distribution, where our lack of interest in a predefined on-treatment LDL concentration would make us more aggressive than guidelines on low baseline LDL patients and less aggressive than guidelines on high baseline LDL patients.     

Fluence-response curves and action spectra for the very low fluence and the low fluence response for the induction of kalanchoë seed germination

Germination of Kalanchoë blossfeldiana Poelln. seeds is absolutely light-requiring. Germination of one seed is the result of one out of three reactions, viz. the very low fluence response (VLFR), the low fluence response (LFR) and the high fluence response/high irradiance response. In order to demonstrate the involvement of phytochrome for both photoresponses, i.e. VLFR and LFR, action spectra for induction were determined. Fluence-response data are analyzed by means of probit analysis in order to calculate the seed population parameters, with special attention to μ, or the fluence for half-maximal induction, and B, the slope in the probit diagram. Laser light was used between 620 and 800 nanometers to analyze the VLFR. Phytochrome is responsible for both photoresponses: the VLFR action spectrum demonstrates an exponential decrease in apparent photoconversion cross-section (P_r → P_fr) up to about 800 nanometers. Assuming that P_r:P_fr-X and P_fr:P_fr-X are the effectors for the VLFR and the LFR, respectively, we estimate an average induction threshold of about 0.003% P_r:P_fr for the VLFR and about 1% P_fr:P_fr for the LFR among individuals of the seed population.