Do Bertalanffy's growth curves result from optimal resource allocation?

Bertalanffy's equation is commonly used to model indeterminate growth. Bertalanffy claimed that this growth pattern results from growth potential decreasing with age. An alternative approach provided by life history theory predicts that indeterminate growth is optimal for organisms in a seasonal environment and results not from decreasing growth potential but from allocating increasingly less energy with age into growth, and more into reproduction. Bertalanffy's curves are the result of evolutionary optimization and should not be used in optimization models as an assumption, but they can be used as a tool to describe the indeterminate growth pattern phenomenologically.     

Do partially buried dune plants grow in optimal trajectories?

Plant adaptations minimising costs of burial responses are vital in mobile dune ecosystems. Conventionally, the burial responses of dune plants have been measured as vertical growth. However, a model developed here shows that growth normal to accumulating non-horizontal dune surfaces requires up to 18% less stem production than vertical growth. To determine whether dune plants grow with this optimal geometry a field survey of growth trajectories was made for three coastal plants, and a greenhouse experiment tested whether plants could actively change growth trajectories away from vertical. In the field and greenhouse partial burial resulted in shifts towards vertical growth, indicating that negative gravitropism is the major response to burial, and reduces the amount of stem needed to respond to burial relative to unburied growth trajectories. However, for two species in the field many buried stems grew closer to optimal (shorter) than vertical, mostly on northward, sun-facing dunes. Thus phototropism is the major stimulus for non-vertical growth, and coincides with optimal trajectories on north-facing dunes. Arctotheca populifolia also displayed non-vertical growth after burial on steep south-facing dunes, but responded to burial in the greenhouse with vertical growth. Measurements of the pressure of sand avalanches occurring on dune slipfaces and stem elasticity indicated that deep avalanches were sufficient to orient the flexible shoots of A. populifolia towards optimal trajectories. Thus, dune plants respond to burial by actively modulating growth towards vertical via negative gravitropism, and passively towards non-vertical—more optimal—trajectories via phototropic growth and the influence of sand avalanches.     

Do ectomycorrhizal fungi exhibit adaptive tolerance to potentially toxic metals in the environment ?

The effects of potentially toxic metals on ectomycorrhizal (ECM) fungi and their higher plant hosts are examined in this review. Investigations at a species and community level have revealed wide inter- and intraspecific variation in sensitivity to metals. Adaptive and constitutive mechanisms of ECM tolerance are proposed and discussed in relation to proven tolerance mechanisms in bacteria, yeasts and plants. Problems with methodology and research priorities are highlighted. These include the need for a detailed understanding of the genetic basis of tolerance in the ECM symbiosis, and for studies of ECM community dynamics in polluted sites.     

Do larval fishes exhibit diel drift patterns in a large,turbid river?

Previous research suggested larval fishes do not exhibit a diel drift cycle in turbid rivers (transparency <30 cm). We evaluated this hypothesis in the turbid, lower Missouri River, Missouri. We also reviewed diel patterns of larval drift over a range of transparencies in rivers worldwide. Larval fishes were collected from the Missouri River primary channel every 4 h per 24‐h period during spring‐summer 2002. Water transparency was measured during this period and summarized for previous years. Diel drift patterns were analyzed at the assemblage level and lower taxonomic levels for abundant groups. Day and night larval fish catch‐per‐unit‐effort (CPUE) was compared for the entire May through August sampling period and spring (May – June) and summer (July – August) seasons separately. There were no significant differences between day and night CPUE at the assemblage level for the entire sampling period or for the spring and summer seasons. However, Hiodon alosoides, Carpiodes/Ictiobus spp. and Macrhybopsis spp. exhibited a diel cycle of abundance within the drift. This pattern was evident although mean Secchi depth (transparency) ranged from 4 to 25 cm during the study and was <30 cm from May through August over the previous nine years. Larval diel drift studies from 48 rivers excluding the Missouri River indicated the primary drift period for larval fishes was at night in 38 rivers and during the day for five, with the remaining rivers showing no pattern. Water transparency was reported for 10 rivers with six being <30 cm or ‘low’. Two of these six turbid rivers exhibited significant diel drift patterns. The effect of water transparency on diel drift of larval fishes appears taxa‐specific and patterns of abundant taxa could mask patterns of rare taxa when analyzed only at the assemblage level.     

Do the contour feathers of Cisticolae exhibit adaptations to annual rainfall in their habitats?

Birds of the genus Cisticola occur over most of Southern Africa in varying habitats ranging from low to high altitudes and wet to dry areas causing species to have unique distributions. In order to determine if Cisticolas have evolved species‐specific water repellency and resistance to water penetration compatible with their habitats, we have measured the barb diameter and spacing of abdominal, breast and throat feathers of six cisticola species and related the results to mean annual rainfall and altitudes in five different locations. Water repellency was not significantly associated with altitude or maximum mean summer temperatures. However, water repellency increased markedly with annual rainfall in the 550 to 600 mm/year range for abdominal and breast feathers, but not for throat feathers. This increase was evident both among species occurring at multiple sites and among different species occurring at single sites. However, the two species occurring at the wettest sites showed low water repellency, but increased resistance to water penetration. These findings suggest that water repellency and resistance to water penetration are part of the evolutionary forces that shape the microstructure of Cisticola contour feathers.     

Hydrodynamics of bolus flow—An analytical approach to blood flow in capillaries

A model which was used by Prothero and Burton to simulate a particular configuration in capillary blood vessels is investigated from a hydrodynamic point of view. In this model, the erythrocytes are approximated by rigid pistons, and plasma is assumed to be an incompressible Newtonian fluid. An order of magnitude analysis using the physiologically realistic values for various parameters reduces the exact equations of motion to an equation describing the creeping motion of the fluid. An analytical approach to the solution of the equation is proposed and some results are reported here. The solution of the flow field is given in terms of a stream function which is represented by two infinite series composed of known functions. Two coupled infinite systems of algebraic equations determining the coefficients of the two series have been derived. This method of solution is proposed as an alternative to the entirely numerical procedure of solving the similar problem proposed by Bugliarelloet al. A limiting case of large aspect ratio (the ratio of the axial spacing of the two successive erythrocytes to the capillary diameter) is studied and the solution, valid away from the erythrocyte surface, has been obtained in simple form. It resembles the classical Poisenille flow, but the pressure gradient is related to the erythrocyte speed.     

What can we learn from Einstein and Arrhenius about the optimal flow of our blood?

Background

The oxygen flow in humans and other higher animals depends on the erythrocyte-to-blood volume ratio, the hematocrit. Since it is physiologically favourable when the flow of oxygen transport is maximum it can be assumed that this situation has been achieved during evolution. If the hematocrit was too low, too few erythrocytes could transport oxygen. If it was too high, the blood would be very viscous, so that oxygen supply would again be reduced.

Methods

The theoretical optimal hematocrit can be calculated by considering the dependence of blood viscosity on the hematocrit. Different approaches to expressing this dependence have been proposed in the literature. Here, we discuss early approaches in hydrodynamics proposed by Einstein and Arrhenius and show that especially the Arrhenius equation is very appropriate for this purpose.

Results & conclusions

We show that despite considerable simplifications such as neglecting the deformation, orientation and aggregation of erythrocytes, realistic hematocrit values of about 40% can be derived based on optimality considerations. Also the prediction that the ratio between the viscosities of the blood and blood plasma at high shear rates nearly equals Euler's constant (2.718) is in good agreement with observed values. Finally, we discuss possible extensions of the theory. For example, we derive the theoretical optimal hematocrit for persevering divers among marine mammals to be 65%, in excellent agreement with the values observed in several species.

General significance

These considerations are very important for human and animal physiology since oxygen transport is an important factor for medicine and physical performance.     

Do incremental increases in blood pressure elicit neointimal plaques through endothelial injury?

Fowl (males more than females) show maturation-dependent rises in blood pressure (BP) and formation of neointimal plaques (NPs), resembling balloon catheter injury-induced neointima, in the abdominal aorta (AbA) just above the bifurcation. The plaque comprises neointimal cells containing abundant endoplasmic reticulum and extracellular matrix. Hence, we investigated whether rapid incremental BP increases in male chicks trigger NP formation, possibly via endothelial injury in hemodynamically selective areas. In 6-wk-old chicks (n = 8) treated 4 wk with solvent (Sv; minipump) or arginine supplement (Arg; 0.3% in drinking water), BP increased from 140 +/- 5 to 159 +/- 4 (Sv) and from 138 +/- 4 to 157 +/- 3 (Arg) mmHg, whereas propranolol treatment (Prop, 8 mg.kg(-1).day(-1); minipump) prevented the rise. Arg and Prop groups had, respectively, 73% and 77% smaller (P < 0.05) NP areas and 19% and 25% less (P < 0.01) AbA medial thickness than Sv controls. In 16-wk-old cockerels, established BP remained high after Sv and Arg treatments. In the Prop group, BP decreased, but neither NP area nor medial thickness was lower than in the Sv group, whereas the Arg group showed greater NP area and medial thickness. Pulse pressure, determined by intravascular transducer, increased as the pulse wave descended the aorta. The results suggest that maturation-dependent rises in BP in chicks may trigger NP formation in the lower segment of the AbA, which was prevented by inhibition of BP increase, or via a possible increase in nitric oxide availability. BP reduction exerts no effect once BP reaches a plateau. Involvement of endothelial injury leading to NP formation and hemodynamic forces selective for the lesion-prone area remain to be determined.     

Do cells in a reproductive state exhibit a fermi-pasta-ulam-fröhlich resonance and emit electromagnetic radiation?

Cells in the reproductive state seem to act like small signal generators and emit radiation which is detectable by small polarizable particles nearby in a medium of suitable osmolarity, but very low conductivity. Evidence for this was seen upon using mouse sarcoma (ascites) cells, and by comparing rapidly dividing mouse "L" fibroblasts with confluent ones. Reproducing cells attracted many more highly polarizable BaTiO₃ particles than they did of the much less polarizable BaSO₄ (dielectric constants 4000 and 11, respectively).This preferential attraction of certain cells for highly polarizable small particles is interpreted as due in large measure to the action of dielectrophoresis on a very small scale.evoked by the presence of nonuniform electric fields of cellular origin acting upon the nearby neutral, polarizable particles.a process called microdielectrophoresis. Consideration of the conductive nature of the surrounding medium forces the conclusion that the cell-generated fields must be oscillatory in nature and have a frequency in the order of a megaherz. These observations recall predictions made earlier by Szent-Györgyi on cellular electronic processes, and by Fröhlich on the possibility of Bose-Einstein condensations to a single quantum state of oscillatory ferroelectric character, due to cooperative long-range interactions among dipolar features of cells. The persistence of oscillatory energy in the lower modes is reminiscent of the Fermi-Pasta-Ulam problem.     

Do sharks exhibit heterodonty by tooth position and over ontogeny? A comparison using elliptic Fourier analysis

Tooth morphology is often used to inform the feeding ecology of an organism as these structures are important to procure and process dietary resources. In sharks, differences in morphology may facilitate the capture and handling of prey with different physical properties. However, few studies have investigated differences in tooth morphology over ontogeny, throughout the jaws of a single species, or among species at multiple tooth positions. Bull (Carcharhinus leucas), blacktip (Carcharhinus limbatus), and bonnethead sharks (Sphyrna tiburo) are coastal predators that exhibit ontogenetic dietary shifts, but differ in their feeding ecologies. This study measured tooth morphology at six positions along the upper and lower jaws of each species using elliptic Fourier analysis to make comparisons within and among species over their ontogeny. Significant ontogenetic differences were detected at four of the six tooth positions in bull sharks, but only the posterior position on the lower jaw appeared to exhibit a functionally relevant shift in morphology. No ontogenetic changes in morphology were detected in blacktip or bonnethead sharks. Intraspecific comparisons found that most tooth positions significantly differed from one another across all species, but heterodonty was greatest in bull sharks. Additionally, interspecific comparisons found differences among all species at each tooth position except between bull and blacktip sharks at two positions. These morphological patterns within and among species may have implications for prey handling efficiency, as well as in providing insight for paleoichthyology studies and reevaluating heterodonty in sharks.     

Do P2X purinergic receptors regulate skeletal muscle blood flow during exercise?

Although there is evidence that sympathetic nerves release ATP as a neurotransmitter to produce vasoconstriction via P2X purinergic receptors, the role of these receptors in the regulation of blood flow to exercising skeletal muscle has yet to be determined. We hypothesized that there is tonic P2X receptor-mediated vasoconstriction in exercising skeletal muscle. To test this hypothesis, the effect of P2X receptor blockade on skeletal muscle blood flow was examined in six exercising mongrel dogs. P2X receptor antagonism was accomplished with pyridoxal-phosphate-6-azophenyl-2'4'-disulfonic acid (PPADs). Animals were instrumented chronically with flow probes on the external iliac arteries of both hindlimbs and a catheter in one femoral artery. PPADs (40 mg) was infused as a bolus into the femoral artery catheter during steady-state exercise at 6 miles/h. Intra-arterial infusion of PPADs increased iliac blood flow from 542 +/- 55 to 677 +/- 69 ml/min (P < 0.05) and iliac vascular conductance from 5.17 +/- 0.62 to 6.53 +/- 0.80 ml.min(-1).mmHg(-1). The PPADs infusion did not affect blood flow in the contralateral iliac artery. These data support the hypothesis that P2X purinergic receptors produce vasoconstriction in exercising skeletal muscle.     

Is optimal gene order impossible?

Recent evidence suggests that yeast genes encoding proteins that are present in the same protein complex tend to be linked and to be co-expressed. More generally, we found that genes that are close to each other in the protein interaction network tend to be linked more often than expected and are often co-expressed. Unexpectedly, we found that linked genes in network proximity have unusually high recombination rates. Because high recombination rates are associated with high rates of genome re-organization, our findings might explain why the clustering of genes in proximity in the network is such a weak effect: there could be a co-evolutionary cycle of physical linkage for co-expression, upwards modification of the recombination rate and concomitant break-up of a cluster. Under such a model an "optimal" gene order is never stable.     

Do cancer cells in human and meristematic cells in plant exhibit similar responses toward plant extracts with cytotoxic activities?

We examined the effect of water extracts of Persea americana fruit, and of the leaves of Tabernamontana divericata, Nerium oleander and Annona cherimolia (positive control) on Vicia faba root cells. We had confirmed in our previously published data the cytotoxicity of these plant extracts on four human cancer cell lines: liver (HepG-2), lung (A549), colon (HT-29) and breast (MCF-7). Vicia faba roots were soaked in plant extracts at dilutions of 100, 1,250, 2,500, 5,000, 10,000, 20,000 ppm for 4 and 24 h. All treatments resulted in a significant reduction in the mitotic index in a dose dependant manner. Root cells treated with T. divericata, N. oleander and A. cherimolia exhibited a decrease in prophase cell percentage, increase in micronuclei and chromosomal abnormalities as concentration increased. The P. americana treatment showed the highest cytotoxic effect on cancer cells, prophase cell percentage increased linearly with the applied concentration and no micronuclei were detected. This study shows that root tip assay of beans can be used in initial screening for new plant extracts to validate their use as candidates for containing active cytotoxic agents against malignant cells. This will greatly help in exploring new plant extracts as drugs for cancer treatment.     

What is optimal about motor control?

This article poses a controversial question: is optimal control theory useful for understanding motor behavior or is it a misdirection? This question is becoming acute as people start to conflate internal models in motor control and perception (Poeppel et?al., 2008; Hickok et?al., 2011). However, the forward models in motor control are not the generative models used in perceptual inference. This Perspective tries to highlight the differences between internal models in motor control and perception and asks whether optimal control is the right way to think about things. The issues considered here may have broader implications for optimal decision theory and Bayesian approaches to learning and behavior in general.