Atlantic salmon Salmo salar in the chalk streams of England are genetically unique.

Recent research has identified genetic groups of Atlantic salmon Salmo salar that show association with geological and environmental boundaries. This study focuses on one particular subgroup of the species inhabiting the chalk streams of southern England, U.K. These fish are genetically distinct from other British and European S. salar populations and have previously demonstrated markedly low admixture with populations in neighbouring regions. The genetic population structure of S. salar occupying five chalk streams was explored using 16 microsatellite loci. The analysis provides evidence of the genetic distinctiveness of chalk-stream S. salar in southern England, in comparison with populations from non-chalk regions elsewhere in western Europe. Little genetic differentiation exists between the chalk-stream populations and a pattern of isolation by distance was evident. Furthermore, evidence of temporal stability of S. salar populations across the five chalk streams was found. This work provides new insights into the temporal stability and lack of genetic population sub-structuring within a unique component of the species' range of S. salar.

FishMORPH - An agent-based model to predict salmonid growth and distribution responses under natural and low flows.

Predicting fish responses to modified flow regimes is becoming central to fisheries management. In this study we present an agent-based model (ABM) to predict the growth and distribution of young-of-the-year (YOY) and one-year-old (1+) Atlantic salmon and brown trout in response to flow change during summer. A field study of a real population during both natural and low flow conditions provided the simulation environment and validation patterns. Virtual fish were realistic both in terms of bioenergetics and feeding. We tested alternative movement rules to replicate observed patterns of body mass, growth rates, stretch distribution and patch occupancy patterns. Notably, there was no calibration of the model. Virtual fish prioritising consumption rates before predator avoidance replicated observed growth and distribution patterns better than a purely maximising consumption rule. Stream conditions of low predation and harsh winters provide ecological justification for the selection of this behaviour during summer months. Overall, the model was able to predict distribution and growth patterns well across both natural and low flow regimes. The model can be used to support management of salmonids by predicting population responses to predicted flow impacts and associated habitat change.

Development of schooling behaviour during the downstream migration of Atlantic salmon Salmo salar smolts in a chalk stream.

The downstream migratory behaviour of wild Atlantic salmon Salmo salar smolts was monitored using passive integrated transponder (PIT) antennae systems over 10 years in the lower reaches of a small chalk stream in southern England, U.K. The timing of smolt movements and the likely occurrence of schooling were investigated and compared to previous studies. In nine of the 10 consecutive years of study, the observed diel downstream patterns of S. salar smolt migration appeared to be synchronized with the onset of darkness. The distribution of time intervals between successive nocturnal detections of PIT-tagged smolts was as expected if generated randomly from observed hourly rates. There were, however, significantly more short intervals than expected for smolts detected migrating during the day. For each year from 2006 to 2011, the observed 10th percentile of the daytime intervals was <4 s, compared to ≥55 s for the simulated random times, indicating greater incidence of groups of smolts. Groups with the shortest time intervals between successive PIT tag detections originated from numerous parr tagging sites (used as a proxy for relatedness). The results suggest that the ecological drivers influencing daily smolt movements in the lower reaches of chalk stream catchments are similar to those previously reported at the onset of migration for smolts leaving their natal tributaries; that smolts detected migrating during the night are moving independently following initiation by a common environmental factor (presumably darkness), whereas those detected migrating during the day often move in groups, and that such schools may not be site (kin)-structured. The importance of understanding smolt migratory behaviour is considered with reference to stock monitoring programmes and enhancing downstream passage past barriers.

Hot spring siliceous stromatolites from Yellowstone National Park: assessing growth rate and laminae formation.

Stromatolites are commonly interpreted as evidence of ancient microbial life, yet stromatolite morphogenesis is poorly understood. We apply radiometric tracer and dating techniques, molecular analyses and growth experiments to investigate siliceous stromatolite morphogenesis in Obsidian Pool Prime (OPP), a hot spring in Yellowstone National Park. We examine rates of stromatolite growth and the environmental and/or biologic conditions that affect lamination formation and preservation, both difficult features to constrain in ancient examples. The "main body" of the stromatolite is composed of finely laminated, porous, light-dark couplets of erect (surface normal) and reclining (surface parallel) silicified filamentous bacteria, interrupted by a less-distinct, well-cemented "drape" lamination. Results from dating studies indicate a growth rate of 1-5 cm year(-1) ; however, growth is punctuated. (14)C as a tracer demonstrates that stromatolite cyanobacterial communities fix CO(2) derived from two sources, vent water (radiocarbon dead) and the atmosphere (modern (14)C). The drape facies contained a greater proportion of atmospheric CO(2) and more robust silica cementation (vs. the main body facies), which we interpret as formation when spring level was lower. Systematic changes in lamination style are likely related to environmental forcing and larger scale features (tectonic, climatic). Although the OPP stromatolites are composed of silica and most ancient forms are carbonate, their fine lamination texture requires early lithification. Without early lithification, whether silica or carbonate, it is unlikely that a finely laminated structure representing an ancient microbial mat would be preserved. In OPP, lithification on the nearly diurnal time scale is likely related to temperature control on silica solubility.

Biological responses to the chemical recovery of acidified fresh waters in the UK.

We report biological changes at several UK Acid Waters Monitoring Network lakes and streams that are spatially consistent with the recovery of water chemistry induced by reductions in acid deposition. These include trends toward more acid-sensitive epilithic diatom and macroinvertebrate assemblages, an increasing proportional abundance of macroinvertebrate predators, an increasing occurrence of acid-sensitive aquatic macrophyte species, and the recent appearance of juvenile (<1 year old) brown trout in some of the more acidic flowing waters. Changes are often shown to be directly linked to annual variations in acidity. Although indicative of biological improvement in response to improving water chemistry, "recovery" in most cases is modest and very gradual. While specific ecological recovery endpoints are uncertain, it is likely that physical and biotic interactions are influencing the rate of recovery of certain groups of organisms at particular sites.

Thermography and the sensory dermatome.

The basic neuroanatomic and physiologic aspects of the sympathetic outflow to the limbs are reviewed and correlated with the somatic sensory dermatomes. The recent literature is considered. A thermocouple thermometer was used to test 30 normal patients and 87 patients with clinically proven nerve root lesions. Thermographic imaging of the sensory dermatome is not plausible, and thermography is not recommended for clinical documentation of painful conditions of the neck, back, or limbs.

Erythrocyte volume, plasma volume, and acid-base changes in exercise and heat dehydration.

Variations in erythrocyte volume [mean corpuscular volume (MCV)] were evaluated during exercise and heat stress to determine the influence on calculated plasma volume and content changes. The results of this study on 17 men indicate that the human red blood cell can increase, decrease, or remain constant in volume during physical stress depending on the combined interactions of plasma osmolality and blood pH. Shrinking of MCV can occur when the increase in plasma osmolality is larger than 5 mosmol/kg H2O and the blood pH remains within 0.1 pH units of its resting value. Erythrocyte swelling is usually noticed with maximal exercise when the blood pH is less than 7.10, in spite of 20 mosmol/kg H20 increments in plasma osmolality. The regression equations indicate that during 30 min of exercise in a cool environment the plasma shifts calculated by either the hematocrit or the hematocrit + hemoglobin method fall within 1% of each other, but during resting heat exposure the hematocrit technique under-estimates the fluid shift by 2.5-3.0%. Application of these considerations to the calculation of plasma content changes during stress made it clear that the pattern of plasma potassium content is quite different with maximal as compared with submaximal exercise.

Fluid-electrolyte shifts and thermoregulation: Rest and work in heat with head cooling.

Plasma volume and thermoregulatory responses were measured, during head and neck cooling with a liquid-cooled neoprene headgear, in four men (21-43 years old) during 60 min of rest, 60 min of ergometer exercise (45% VO2 max), and 30 min of recovery in the supine position at 40.1 degrees C DBT and 40% rh. Compared with control (noncooling) responses, cooling decreased thigh sweating and increased mean skin temperature (Tsk) at rest, and attenuated the increases in thigh sweating by 0.26 mg/min x cm2 (-22.4%, p < 0.05), heart rate by 10 b/min (-8.5%, N.S.), rectal temperature (Tre) by 0.3 degrees C (N.S.), and ventilation by 12.5% (N.S.) during exercise. In recovery, cooling facilitated the decreases in thigh sweat rate, heart rate, Tre, and forearm blood flow, and enhanced the increase in Tsk toward control levels. Cooling had no effect upon plasma protein, osmotic, or electrolyte shifts during rest, exercise, or recovery. Plasma volume (PV) loss during exercise was 11.2% without cooling and 10.9% with cooling. Cooling increased PV by 3% (p < 0.05) during rest, and this differential was maintained throughout the exercise and recovery periods.

Plasma volume and electrolyte shifts with heavy exercise in sitting and supine positions.

Plasma volume (PV) and electrolyte shifts were measured before and for 60 min after a continuous peak oxygen uptake (VO2 peak) test in four men (26-45 yr) on a bicycle ergometer. Mean (+/-SE) sitting VO2peak (3.16 +/- 0.32 1/min) was the same as supine VO2peak (3.13 +/- 0.33 1/min). In recovery (R + 1.5 min), mean PV had decreased by 477 ml (-16.1%, P less than 0.05) in the sitting and by 548 ml (-17.6%, P less than 0.05) in the supine positions, whereas total osmolality increased progressively with its peak at R + 3.5 min. The percentage losses of protein, total Ca2+, and ionized Cai2+ were about half as great as the percentage loss in PV, indicating a selective retention of these constituents. Calculated osmolality (sigma Na+, K+, Cl-, Cai2+) returned to control levels within 1.5 min after sitting exercise but required about 15 min after supine exercise. These small increases in protein concentration were not likely to significantly aid restitution of plasma volume and the ions were probably in equilibrium across the capillary membrane. So a change in hydrostatic and/or systemic blood pressures most likely provided the force for restitution of plasma volume.

Fluid and electrolyte shifts during bed rest with isometric and isotonic exercise.

Fluid and electrolyte shifts were measured in seven men (19-21 yr) during three 2-wk bed rest (BR) periods, each of which was separated by a 3-wk ambulatory recovery period. During two of the three BR periods they performed isometric exercise and isotonic exercise. No prescribed exercise was given during the other BR period. On day 4 of BR, plasma volume decreased (P less than 0.05) 441 ml (-12.6%) with no exercise, 396 ml (-11.3%) with isometric, and 262 ml (-7.8%) with isotonic exercise; the decreases (NS) of extracellular volume were -4.4%, -2.6%, and -2.7%, respectively. By day 13 of BR, plasma volume stabilized at the lower level with isometric and isotonic exercise and continued to decline with no exercise; but the extracellular volume returned to or above control levels due to an overshoot of the interstitial volume of +320 to +430 ml (2.0-2.7%) that was about equal to the plasma volume loss. During BR there were isocontent losses from the plasma of protein, albumin, globulin, urea N2, uric acid, creatinine, Na, Cl, osmolarity, P, and glucose that were not influenced by either exercise regimen. However, the blood, red blood cell, and plasma volumes, and the Ca and K contents were stabilized during BR by both exercise regimens. The results suggest that during BR, preservation of the extracellular volume takes precedence over maintenance of the plasma volume, and this mechanism is independent of the effects of isometric or isotonic exercise.

+Gz tolerance in man after 14-day bedrest periods with isometric and isotonic exercise conditioning.

The purpose of this study was to determine the effects of isometric or isotonic exercise training on post-bedrest +Gz tolerance. Seven male volunteers, 19-22 years, underwent accelerations of +2.1 Gz (740 s), +3.2 Gz (327 s), and +3.8 Gz (312 s) in a selected, randomized order; the ramp to peak acceleration was 1.8 G/min. The centrifugation runs were terminated by loss of central vision (blackout) to a white light with a luminance of 3.15 times 10-5 log candle/cm-2 (0.092 ft-lambert). The study began with a 14-d ambulatory control period, followed by three 14-d bedrest periods (each separated by a 21-d recovery period) and then a final week of recovery. During the ambulatory periods, the subjects exercised on a bicycle ergometer at 50% of their maximal oxygen uptake (max VO2) for 1 h/d. During two of the three bedrest periods, the subjects performed in the supine position one of two routines, either isometric exercise (21% of max leg extension force for 1 min followed by 1-min rest) or isotonic exercise (68% of max VO2) for 0.5 in the morning and afternoon. During the third bedrest period, no exercise was performed. In general +Gz tolerance was reduced by 24% to 35% (p less than or equal to 0.05) after bedrest. Compared with control values, there were significant reductions in average tolerance times after bedrest with no exercise and isotonic exercise at all G levels. With isometric exercise, there was a significant decrease in tolerance at 2.1 Gz but not at 3.2 Gz or 3.8 Gz, even though the latter tolerances were reduced 15.6% and 10.0%, respectively. Both exercise regimens maintained tolerance at levels equal to or above that obtained with no exercise. Compared with control values, average tolerances were lower (p less than or equal to 0.05) after the two recovery periods between the bedrest periods (minus 24% to minus 26% at 3.2 Gz and 3.8 Gz), indicating that 3 weeks of ambulation was not sufficient time for full recovery from the deconditioning induced in this study. A prediction equation was constructed with data from all comparable studies utilizing deconditioned men riding relaxed without protective garments: Tolerance (in seconds) equals minus 334 + (1715/+Gz level). From this equation, the calculated tolerance after bedrest is 13.5 min at 1.5 G, and the point of zero tolerance is 5.1 Gz.