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  • 11
    Electronic Resource
    Electronic Resource
    Population genetics of the Antarctic heteronemertean Parbolasia corrugatus from the South Orkney Islands (1998)
    Springer
    Marine biology 131 (1998), S. 1-13 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract An allozyme survey, using starch-gel electrophoresis, was carried out on eight populations of the Antarctic nemertean worm Parborlasia corrugatus (McIntosh, 1876) collected from locations around the South Orkney Islands, Antarctica. These populations were separated by distances in the order of tens of kilometres. Genetic variation was estimated over 22 enzyme loci for all populations examined, giving an observed heterozygosity of 0.142. This was much lower than the expected heterozygosity (H e  = 0.201), and it was found that there was a significant deficiency of het‐erozygotes across four enzyme loci ( p ≤ 0.01). A more detailed examination of this deficiency of heterozygotes was undertaken for the six populations and six variable enzyme loci for which the most complete data sets existed. A significant deficiency of heterozygotes was found at the enzyme locus Odh-1 for four of the six populations examined ( p ≤ 0.01). Mean F is (0.240) indicated a significant ( p ≤ 0.01) within-population component of the heterozygote deficiency estimated for the six populations sampled, and this was mainly due to the␣Ap-1, Odh-1 and Pgm-1 loci. The mean F st value (0.036) was also significant ( p ≤ 0.01), indicating a degree of genetic differentiation between populations. The observed levels of genetic differentiation between populations of P. corrugatus and the significant heterozygote deficiencies were unexpected, because this species has been reported to have a long-lived planktotrophic larva. It is hypothesised that recruitment of P. corrugatus in the South Orkney Islands originates from genetically distinct populations located in the Weddell Sea and to the west of the Antarctic Peninsula. Shifts in the relative position of the Weddell Sea Front, Weddell–Scotia Confluence and Scotia Front, relative to the South Orkney Islands, provide a mechanism for variation in the origin of recruits over time.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002270050290
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  • 12
    Electronic Resource
    Electronic Resource
    The nature of heat coma in Littorina littorea (Mollusca: Gastropoda) (2000)
    Springer
    Marine biology 137 (2000), S. 447-451 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  The nature of heat coma was examined in the edible periwinkle Littorina littorea (L.). Duration of acclimation did not influence heat-coma temperature at 12 °C, although other acclimation temperatures were important in influencing thermal tolerance, with positive shifts in coma temperature observed in response to elevated temperatures. Previous thermal history also influenced heat-coma temperatures. Individuals subjected to repeat heat-coma events on a daily basis showed significant declines (P 〈 0.05) in coma-temperature; in contrast individuals exposed to repeat heat-coma events on a weekly basis showed no decline in thermal tolerance. Size-effects occurred at selected sites, where decreased heat-coma temperatures were recorded in large individuals.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002270000367
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  • 13
    Electronic Resource
    Electronic Resource
    Assimilation efficiency of the antarctic marine isopod Glyptonotus antarcticus (1979)
    Springer
    Marine biology 52 (1979), S. 157-160 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract When fed shrimp every 2 days, the isopod Glyptonotus antarcticus Eights assimilated over 90% of the ingested food. Errors in this estimate due to loss of food material during maceration by G. antarcticus were investigated and allowed for. These results are discussed in relation to data for other isopods and marine invertebrates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00390423
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  • 14
    Electronic Resource
    Electronic Resource
    Seasonality of polypide recycling and sexual reproduction in some erect Antarctic bryozoans (1998)
    Springer
    Marine biology 131 (1998), S. 647-658 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The seasonality of polypide cycling has been investigated for three species of erect bryozoans from Antarctica: Isoseculiflustra rubefacta (Kluge, 1914), Nematoflustra flagellata (Waters, 1904) and Himantozoum antarcticum (Calvet, 1905). Approximately ten colonies of each species were collected monthly by SCUBA divers over a 14 mo period during 1992/1993, and the status of each individual zooid was classified as differentiating/regenerating, active (feeding autozooids), degenerate (brown body) or sexually reproductive (ovicells present, or zooid containing a larva). Polypide cycling in all three species was distinctly seasonal. New zooids formed at the growth margin and typically contained actively feeding polypides for ≃9 mo before these polypides degenerated into brown bodies in the austral winter (June). Very few polypides were active in the period from June to August, when water-column food levels were at their lowest; after this period new polypides differentiated. Individual zooids typically underwent a total of five (I. rubefacta and N. flagellata), or at least four (H. antarcticum) complete polypide cycles before becoming senescent. Polypide lifetimes generally became shorter as the age of the zooid increased. Sexual reproduction was also distinctly seasonal in these species, with bands of ovicells or sexually reproductive zooids being formed each year in late summer once a given colony had grown to a threshold size (or age). Larvae were then brooded for ≃10 mo before being released in January/February (N. flagellata) or February/March (H. antarcticum). The seasonal patterns of polypide cycling are related clearly to the variations in food availability, and these species appear to have the longest zooid lifetime (≃5 yr) and the slowest polypide cycling (once per year with polypide lifetimes up to 10 mo) reported for any bryozoan so far.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002270050357
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  • 15
    Electronic Resource
    Electronic Resource
    Vestibulo-oculomotor testing during the course of a spaceflight mission (1993)
    Springer
    Journal of molecular medicine 71 (1993), S. 740-748 
    Details
    ISSN: 1432-1440
    Keywords: Weightlessness ; Vestibular adaptation ; Caloric testing ; Vestibulo-ocular reflex ; Ocular torsion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The experimental concept and findings from a recent manned orbital spaceflight are presented. In a single-case, longitudinal study, vestibulo-oculomotor function was examined by caloric testing and active head oscillations. The results from preflight, inflight, and postflight measurements of the human vestibulo-ocular reflex, together with those of ongoing terrestrial studies, should enable separation of the canalicular and otolithic contributions to ocular torsion. This analysis enables an accurate evaluation of the adaptation of the otolithic system to the inflight microgravity and, after landing, to the 1- force environment. Video-oculography was employed throughout for the comprehensive measurement of eye and head movements. Caloric testing involved air insufflation at 15° C over 90 s, followed by an observation interval of 2 min. During inflight testing this was continued with a 30-s free-floating interval. Active head oscillations were performed at four discrete frequencies (0.12, 0.32, 0.80, 2.0 Hz) and over a frequency sweep between 0.1 and 2.0 Hz. These head oscillations were performed in yaw, pitch, and roll and for three visual conditions (head-fixed target, space-fixed target, no target). The concomitant stimulation of the semicircular canals and otolithic receptors during these oscillations should yield different oculomotor responses under 1-g and 0-g adaptations. Both the short-form caloric test and the active head movement test were performed on 4 of the 5 available mission days. The results of the caloric tests yield a caloric nystagmus intensity (slow-phase velocity) of approximately 60% of that measured before flight and indicate an adaptation in response over the 10-day period after landing. The preliminary results from the head movement tests about the roll axis indicate an adaptive response in this aspect of the vestibulo-ocular reflex during prolonged microgravity. Some changes in sensomotoric control were also apparent during the inflight and postflight phases.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00209729
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  • 16
    Electronic Resource
    Electronic Resource
    Charcot-Marie-Tooth disease 1A (CMT1A) associated with a maternal duplication of chromosome 17p11.2→12 (1993)
    Springer
    Human genetics 〈Berlin〉 91 (1993), S. 392-394 
    Details
    ISSN: 1432-1203
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract We report here the second case of Charcot-Marie-Tooth disease 1A (CMT1A) with a cytogenetically visible de novo direct duplication of 17p11.1→17p12. A male child who was initially referred for developmental delay and dysmorphism was subsequently shown to have significantly reduced motor nerve conduction velocities characteristic of CMT1A. This patient was not informative for the DNA markers mapping to the CMT1A region; however, with DNA markers pA10–41 and EW503 that map proximally and distally with respect to the disease locus, a dosage difference was observed between the two alleles. Comparison with parental genotypes indicated a de novo maternal duplication. Pulsed field gel analysis using probe VAW409R3a indicated that a 500-kb SacII junction fragment usually associated with CMT1A was absent in this patient. These findings confirm that the disease phenotype is probably caused by a gene dosage effect.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00217365
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  • 17
    Electronic Resource
    Electronic Resource
    The cryopreservation of Chlorella (1977)
    Springer
    Archives of microbiology 114 (1977), S. 249-254 
    Details
    ISSN: 1432-072X
    Keywords: Chlorella ; Cryopreservation ; Fatty acid analysis ; Preeze-fracture electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Following a shift from autotrophic to heterotrophic nutrition, cells of Chlorella protothecoides become sensitive to the stresses of freezing and thawing. The injury then observed at slow rates of cooling cannot be explained by the cellular response to hypertonic solutions, and at faster cooling rates intracellular ice formation was not demonstrated to be damaging. These findings are at variance with suggested mechanisms of injury in other cellular systems. The results are compared with alterations in ultrastructure and in the composition of the cellular fatty acids.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00446869
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  • 18
    Electronic Resource
    Electronic Resource
    The cryopreservation ofChlorella (1978)
    Springer
    Archives of microbiology 119 (1978), S. 153-156 
    Details
    ISSN: 1432-072X
    Keywords: Chlorella ; Cryopreservation ; Fatty acids analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Following growth under sub-optimal concentrations of nutrients, cells ofChlorella emersonii accumulated lipid and became more resistant to the damage caused by freezing and thawing. These results suggest that the factor responsible for the cold hardening of someChlorella spp is not the effect of low temperatures per se but simply that of the reduced metabolic rate. Evidence is given that the post-thaw injury observed following rapid rates of cooling is associated with the vacuole.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00964266
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  • 19
    Electronic Resource
    Electronic Resource
    Unilateral testing of utricular function (1998)
    Springer
    Experimental brain research 121 (1998), S. 457-464 
    Details
    ISSN: 1432-1106
    Keywords: Key words Otolith-ocular response ; Utricle ; Unilateral function ; Eccentric rotation ; Video-oculography
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  A modified rotatory chair test is reported in which radial acceleration, generated by eccentric displacement of the subject during constant angular velocity, is exploited as a unilateral stimulation to the otolith organs. During constant angular rate rotation, the test subject is displaced laterally on the rotating turntable by 3.5 cm, so that one labyrinth becomes aligned with the rotatory axis while the second – eccentric – labyrinth is solely exposed to the altered gravito-inertial acceleration (GIA). Previously reported results showed that the direction of the response is independent of the direction of turntable rotation, ruling out any canal influence, and indicated that in a normal population the response, measured in one eye, was symmetrical for displacement of the left and right labyrinths. This mode of stimulus thus appears to elicit a unilateral otolith-ocular response (OOR). Examination of this unilateral OOR was extended in the present study; comparative testing with head-tilt to gravity, i.e. involving bilateral stimulation to the otolith organs, was carried out. Movements of both eyes were recorded (by three-dimensional video-oculography), in order to examine response conjugacy. To verify the specificity of the unilateral stimulus, tests were performed with patients who had previously undergone unilateral section of the vestibular nerve as treatment for acoustic neuroma. The eccentric displacement profile (EDP) and head-tilt stimulus each included ten cycles of left-right oscillation in order to permit signal averaging. In the normal subjects (n=12) the torsional component of the OOR proved to be both labyrinth-symmetrical and conjugate, during both bilateral and unilateral otolith stimulation. OOR gain (ocular torsion/GIA tilt) was higher for bilateral than unilateral stimulation. Bilateral OORs, obtained from three of the five unilaterally deafferented patients, proved less symmetrical and conjugate than in the normals. Unilateral OORs in all five patients were characteristically asymmetrical, with little or no response during stimulation of the diseased labyrinth.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002210050481
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  • 20
    Electronic Resource
    Electronic Resource
    European vestibular experiments on the Spacelab-1 mission: 3. Caloric nystagmus in microgravity (1986)
    Springer
    Experimental brain research 64 (1986), S. 255-263 
    Details
    ISSN: 1432-1106
    Keywords: Caloric stimulation ; Microgravity ; Nystagmus ; Bárány ; Spacelab 1 ; Orbital flight
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Response to caloric stimulation was examined in two subjects in the weightless environment of orbital flight. Using air insufflation, a binaural temperature stimulus profile was performed twice on each subject during flight. In all but one test, which was carried out on the first mission day, a caloric nystagmus was registered. This zero-g nystagmus was similar to ground-based pre and postflight responses with regard to its intensity, its temporal correlation with the stimulus profile (nystagmus was always directed towards the warmer ear) and the subjective sensations reported by the tested subjects. These findings demonstrate that mechanisms other than thermoconvection are involved in the elicitation of the caloric nystagmus response. At each stage of the temperature stimulus profile, linear acceleratory stimulation was presented in the form of oscillations in the X-axis. Some differences were found between one-g and zero-g conditions in the resultant modification of the nystagmus response.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00237741
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