Seasonal Patterns of Abundance of Tundra Arthropods near Barrow

Arthropods active on the surface of the tundra near Barrow, Alaska, were trapped throughout four summer seasons (1966-1969), using "sticky-board" traps. More than 95% of the arthropods (excluding Acarina and Collembola) captured were of the order Diptera. Adults of most species of Diptera emerged in the middle two weeks of July; the abundance of arthropods on the tundra surface was maximal at that time. Year-to-year variations in abundance of various arthropod taxa are related to prevailing weather conditions and to the cycle of tundra disturbance and recovery associated with the abundance of brown lemmings.Modalités de l’abondance des arthropodes de la toundra selon les saisons, près de Barrow.  Près de Barrow, Alaska, on a, ou cours des quatre étés (1966-1969), capturé au moyen de pièges à glu les arthropodes actifs à la surface de la toundra.  Plus de 95 pour cent des arthropodes capturés (à l’exclusion des Acariens et des Collemboles) appartenaient à l’ordre des Diptères.  Les adultes de la plupart des espèces de Diptères apparaissaient au cours des deux semaines du milieu de juillet : c’est à ce moment que les arthropodes étaient les plus nombreux à la surface de la toundra.  Les variations annuelles d’abondance des divers taxa d’arthropodes sont liées aux conditions du temps et au cycle de déprédation et de reprise de la toundra selon l’abondance des lemmings

Sympathetic activation in exercise is not dependent on muscle acidosis: Direct evidence from studies in metabolic myopathies

Muscle acidosis has been implicated as a major determinant of reflex sympathetic activation during exercise. To test this hypothesis we studied sympathetic exercise responses in metabolic myopathies in which muscle acidosis is impaired or augmented during exercise. As an index of reflex sympathetic activation to muscle, microneurographic measurements of muscle sympathetic nerve activity (MSNA) were obtained from the peroneal nerve. MSNA was measured during static handgrip exercise at 30% of maximal voluntary contraction force to exhaustion in patients in whom exercise-induced muscle acidosis is absent (seven myophosphorylase deficient patients; MD [McArdle's disease], and one patient with muscle phosphofructokinase deficiency [PFKD]), augmented (one patient with mitochondrial myopathy [MM]), or normal (five healthy controls). Muscle pH was monitored by 31P-magnetic resonance spectroscopy during handgrip exercise in the five control subjects, four MD patients, and the MM and PFKD patients. With handgrip to exhaustion, the increase in MSNA over baseline (bursts per minute [bpm] and total activity [%]) was not impaired in patients with MD (17+/-2 bpm, 124+/-42%) or PFKD (65 bpm, 307%), and was not enhanced in the MM patient (24 bpm, 131%) compared with controls (17+/-4 bpm, 115+/-17%). Post-handgrip ischemia studied in one McArdle patient, caused sustained elevation of MSNA above basal suggesting a chemoreflex activation of MSNA. Handgrip exercise elicited an enhanced drop in muscle pH of 0.51 U in the MM patient compared with the decrease in controls of 0.13+/-0.02 U. In contrast, muscle pH increased with exercise in MD by 0.12+/-0.05 U and in PFKD by 0.01 U. In conclusion, patients with glycogenolytic, glycolytic, and oxidative phosphorylation defects show normal muscle sympathetic nerve responses to static exercise. These findings indicate that muscle acidosis is not a prerequisite for sympathetic activation in exercise

Swimming speed of three species of Alexandrium as determined by digital in-line holography.

Digital in-line holographic (DIH) microscopy was used to track motility in several related species of the marine dinoflagellate Alexandrium in response to temperature after acclimation at selected temperatures. Numerical reconstruction of DIH holograms yielded high-contrast three-dimensional images of the trajectories of many motile cells swimming simultaneously throughout the sample volume. Swimming speed and trajectory were determined for clonal isolates of A. ostenfeldii, A. minutum and A. tamarense within the temperature range from 8 to 24\ub0C. The strains of these species revealed differences in temperature optima for growth and tolerance that were a function of both acclimation responses and genetic factors reflecting the origin of the isolates. The fastest swimming speeds were recorded at 24\ub0C for cells of A. minutum. Acclimated strains of all three species swam significantly slower at lower temperatures, although fastest swimming speeds did not always occur at temperature optima for growth. Aged cells from stationary phase cultures swam more slowly than cells in exponential growth phase. Doublets from a rapidly dividing culture swam faster than singlets from the same culture, confirming the propulsive advantage of paired cells. Holographic microscopy is a powerful tool for the acquisition of detailed observations of swimming behaviour of microalgal cells in the form of three-dimensional trajectories over the appropriate temporal (sub-second) and spatial (micrometer) scales.Peer reviewed: NoNRC publication: Ye