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  • Aerospace Medicine  (9)
  • Hemiparasitism  (3)
  • Aldabra  (1)
  • 1
    Digitale Medien
    Digitale Medien
    Springer
    Oecologia 86 (1991), S. 81-87 
    ISSN: 1432-1939
    Schlagwort(e): Competition ; Hemiparasitism ; Host selectivity ; Rhinanthus
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary Rhinanthus minor (Yellow-rattle) was grown in replacement series mixtures with Lolium perenne and Trifolium repens. The hemiparasitic interaction resulted in Relative Yield Totals (the sum of the yields in mixture relative to those in monoculture) considerably above 2. The hemiparasite caused a greater decrease in the yield of the legume and also performed better on the legume, indicating that T. repens was a better host for R. minor than L. perenne under the experimental conditions. When L. perenne and T. repens were grown in binary mixture with or without R. minor the hemiparasite affected considerably the competitive relationship between the two species by selectively parasitizing the legume. The effect of R. minor on competition between the two species was, however, dependent upon the nutrient status of the soil: the higher the level of soil nitrogen the fewer haustorial connections were made with T. repens and the less was the depression in its yield. In another series of experiments in which Festuca rubra, Holcus lanatus and L. perenne were grown in various binary mixtures with or without R. minor it was also shown that the yield of a preferred host was depressed to the advantage of a non-preferred host. It is suggested that the mediation of competition by the hemiparasite provides a mechanism by which it might affect the structure and diversity of plant communities.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    Springer
    Oecologia 89 (1992), S. 62-68 
    ISSN: 1432-1939
    Schlagwort(e): Rhinanthus ; Hemiparasitism ; Species diversity ; Community structure
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary Rhinanthus minor (yellow-rattle) is a widespread hemiparasitic plant of grassland habitats throughout Great Britain. It is usually considered to be indicative of species-rich grassland, but in a survey of 14 habitats throughout Britain it was found that R. minor at the time of flowering normally occupied relatively low-diversity patches within areas of high diversity as determined by the number of species, Simpson's Index and the Shannon-Wiener Index. Following the death of adult plants of R. minor in the summer it was shown that the pattern of species diversity changed such that by the time R. minor germinated in the following spring the differences between the areas containing and not containing R. minor were much less distinct. A perturbation experiment in which R. minor was removed from four sites indicated that the effect of the removal of R. minor on the development of community structure over the next year was to increase species diversity on three of the sites and decrease it on the fourth. Those species which responded to the removal of R. minor by an increase in abundance were shown to be preferred hosts. All three lines of evidence point to the fact R. minor has a significant effect on the species diversity of the communities in which it grows by selectively parasitizing components of the flora and modifying the competitive relationships between plants. However, as the communities generally responded to the removal of R. minor by an increase in diversity and as the general survey indicated that R. minor is generally associated with areas of low diversity it would appear that the plants which are selectively parasitized are generally not the competitive dominants in the community.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    Springer
    Oecologia 78 (1989), S. 401-406 
    ISSN: 1432-1939
    Schlagwort(e): Rhinanthus ; Hemiparasitism ; Host selectivity
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary Rhinanthus minor (Yellow-rattle) is a widespread hemiparasitic plant of grassland habitats throughout Britain. Association analysis of the dune vegetation at Holme-next-the-Sea in eastern England revealed only two potential host plants through positive association. In contrast direct examination of the root systems revealed haustorial connections with 20 host species. The number of species parasitized by one plant ranged from one to seven. Data from another four sites in Britain and one in central Europe indicate that the natural host range of R. minor encompasses at least 50 species from 18 families with 22% in the Leguminosae and 30% in the Gramineae. Comparison of the number of haustorial connections made to each species with the abundance of roots in the soil shows that R. minor is a highly selective parasite, but that the selectivity is not consistent between populations or between plants from different parts of the same population. The reasons for host selectivity are discussed.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 4
    ISSN: 1573-5052
    Schlagwort(e): Aldabra ; Atoll ; Markovian model ; Succession ; Tortolse grazing
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The process of succession after release from grazing by giant tortoises was investigated in three different vegetation types on Aldabra atoll. After four years there was very little change in two vegetation types: a tall mixed scrubland and an open single-species grassland. Probably in the former case grazing had no effect and in the latter case soil nutrients were limiting sward growth and establishment. In the third vegetation type, a patchwork of scrub and low vegetation, analysis of transition matrices showed that the succession was non-independent, non-stationary and depended on more than one past state (high order). This succession was extrapolated by simulation. The results suggested that other vegetation types studied were discrete associations, not merely different stages in the same grazing-mediated sere. The transition matrix approach proved useful in helping to generate initial hypotheses, but became too cumbersome for a realistic model of this succession. An experimental approach will be better for dealing with problems identified from the transition models. We are extremely grateful to the staff of the Seychelles Islands Foundation and of their Aldabra Research Station for permission to work on the island and for their assistance in the field.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 5
    Publikationsdatum: 2019-07-19
    Beschreibung: What is the risk? Given that astronauts exposed to microgravity experience a cephalad fluid shift, and that both symptomatic and asymptomatic astronauts have exhibited optic nerve sheath edema on MRI, there is a high probability that all astronauts have some degree of increased intracranial pressure (ICP; intracranial hypertension), and that those susceptible (via eye architecture, anatomy, narrow optic disc) have a high likelihood of developing papilledema (optic disc edema, globe flattening), choroidal folds, and/or hyperopic shifts and that the degree of edema may determine long-term or permanent vision impairment or loss. Back to back panels on this topic have been developed to address this emerging risk. The first panel will focus on the 6 clinical cases with emphasis on ophthalmic findings and imaging techniques used pre-, in-, and post-flight. The second panel will discuss the operational mitigation and medical requirements, the potential role of CO2 on ISS, and the research approach being developed. In total these back to back panels will explore what is known about this risk, what has been done immediately to address it, and how an integrated research model is being developed.
    Schlagwort(e): Aerospace Medicine
    Materialart: JSC-CN-21948 , 82nd Annual Scientific Meeting of the Aerospace Medical Association; May 08, 2011 - May 12, 2011; Anchorage, AK; United States
    Format: application/pdf
    Standort Signatur Erwartet Verfügbarkeit
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  • 6
    Publikationsdatum: 2019-07-19
    Beschreibung: Intermediates of the one-carbon metabolic pathway are altered in astronauts who experience vision-related issues during and after space flight. Serum concentrations of homocysteine, cystathionine, 2-methylcitric acid, and methylmalonic acid were higher in astronauts with ophthalmic changes than in those without (Zwart et al., J Nutr, 2012). These differences existed before, during, and after flight. Potential confounding factors did not explain the differences. Genetic polymorphisms could contribute to these differences, and could help explain why crewmembers on the same mission do not all have ophthalmic issues, despite the same environmental factors (e.g., microgravity, exercise, diet). A follow-up study was conducted to evaluate 5 polymorphisms of enzymes in the one-carbon pathway, and to evaluate how these relate to vision and other ophthalmic changes after flight. Preliminary evaluations of the genetic data indicate that all of the crewmembers with the MTRR GG genotype had vision issues to one degree or another. However, not everyone who had vision issues had this genetic polymorphism, so the situation is more complex than the involvement of this single polymorphism. Metabolomic and further data analyses are underway to clarify these findings, but the preliminary assessments are promising.
    Schlagwort(e): Aerospace Medicine
    Materialart: JSC-CN-32354 , Experimental Biology; Mar 28, 2015 - Apr 01, 2015; Boston, MA; United States
    Format: application/pdf
    Standort Signatur Erwartet Verfügbarkeit
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  • 7
    Publikationsdatum: 2019-08-13
    Beschreibung: Carbon dioxide (CO2) levels on board the International Space Station (ISS) have typically averaged 2.3 to 5.3 mmHg, with large fluctuations occurring over periods of hours and days. CO2 has effects on cerebral vascular tone, resulting in vasodilation and alteration of cerebral blood flow (CBF). Increased CBF leads to elevated intracranial pressure (ICP), a factor leading to visual disturbances, headaches, and other central nervous system symptoms. Ultrasound of the optic nerve and optical coherence tomography (OCT) provide surrogate measurements of ICP; in-flight measurements of both were implemented as enhanced screening tools for the Visual Impairment/Intracranial Pressure (VIIP) syndrome. This analysis examines the relationships between ambient CO2 levels on ISS, ultrasound and OCT measures of the eye in an effort to understand how CO2 may possibly be associated with VIIP and to inform future analysis of in-flight VIIP data.
    Schlagwort(e): Aerospace Medicine
    Materialart: JSC-CN-38407 , 2017 NASA Human Research Program Investigators'' Workshop (HRP IWS 2017); Jan 23, 2017 - Jan 26, 2017; Galveston, TX; United States
    Format: application/pdf
    Standort Signatur Erwartet Verfügbarkeit
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  • 8
    Publikationsdatum: 2019-08-13
    Beschreibung: The Visual Impairment Intracranial Pressure (VIIP) syndrome is currently NASA's number one human space flight risk. The syndrome, which is related to microgravity exposure, manifests with changes in visual acuity (hyperopic shifts, scotomas), changes in eye structure (optic disc edema, choroidal folds, cotton wool spots, globe flattening, and dilated optic nerve sheaths), and in some cases with documented increased intracranial pressure (ICP) postflight. While the eye appears to be the main affected end organ of this syndrome, the ocular effects are thought to be related to underlying changes in the vascular system and the central nervous system. The leading hypotheses for the development of VIIP involve microgravity-induced head-ward fluid shifts along with a loss of gravity-assisted drainage of venous blood from the brain, leading to cephalic congestion, decreased CSF resorption and increased ICP. Since 70% of ISS crewmembers have manifested clinical signs or symptoms of the VIIP syndrome, it is assumed that the majority have some degree of ICP elevation in-flight compared to the ground. Prolonged elevations of ICP can cause long-term reduced visual acuity and loss of peripheral visual fields, and have been reported to cause mild cognitive impairment in the analog terrestrial population of Idiopathic Intracranial Hypertension (IIH). These potentially irreversible health consequences underscore the importance of identifying the factors that lead to this syndrome and mitigating them.
    Schlagwort(e): Aerospace Medicine
    Materialart: JSC-CN-32164 , NASA Human Research Program Investigators'' Workshop; Jan 13, 2015 - Jan 15, 2015; Galveston, TX; United States
    Format: application/pdf
    Standort Signatur Erwartet Verfügbarkeit
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  • 9
    Publikationsdatum: 2019-08-13
    Beschreibung: No abstract available
    Schlagwort(e): Aerospace Medicine
    Materialart: JSC-CN-38572 , NASA Human Research Program Investigators'' Workshop; Jan 23, 2017 - Jan 26, 2017; Galveston, TX; United States
    Format: application/pdf
    Standort Signatur Erwartet Verfügbarkeit
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  • 10
    Publikationsdatum: 2019-08-13
    Beschreibung: Data from the Nutritional Status Assessment protocol provided biochemical evidence that the one-carbon metabolic pathway may be altered in individuals experiencing vision-related issues during and after space flight (1, 2). Briefly, serum concentrations of homocysteine, cystathionine, 2-methylcitric acid, and methylmalonic acid were significantly (P〈0.001) higher (25-45%) in astronauts with ophthalmic changes than in those without such changes (1). These differences existed before, during, and after flight. Serum folate was lower (P〈0.01) during flight in individuals with ophthalmic changes. Preflight serum concentrations of cystathionine and 2-methylcitric acid, and mean in-flight serum folate, were significantly (P〈0.05) correlated with postflight changes in refraction (1). A follow-up study was conducted to evaluate a small number of known polymorphisms of enzymes in the one-carbon pathway, and to evaluate how these relate to vision and other medical aspects of the eye. Specifically, we investigated 5 polymorphisms in MTRR, MTHFR, SHMT, and CBS genes and their association with ophthalmic changes after flight in 49 astronauts. The number of G alleles of MTRR 66 and C alleles of SHMT1 1420 both contributed to the odds of visual disturbances (3). Block regression showed that B-vitamin status at landing and genetics were significant predictors for many of the ophthalmic outcomes studied (3). In conclusion, we document an association between MTRR 66 and SHMT1 1420 polymorphisms and space flightinduced vision changes. These data document that individuals with an altered 1-carbon metabolic pathway may be predisposed to anatomic and/or physiologic changes that render them susceptible to ophthalmic damage during space flight.
    Schlagwort(e): Aerospace Medicine
    Materialart: JSC-CN-34670 , HRP Investigator Workshop; Feb 08, 2016 - Feb 11, 2016; Galveston, TX; United States
    Format: application/pdf
    Standort Signatur Erwartet Verfügbarkeit
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