| 1. |
- Callaghan, Terry V., et al.
(författare)
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Responses to projected changes in climate and UV-B at the species level
- 2004
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Ingår i: Ambio: a Journal of Human Environment. - : Royal Swedish Academy of Sciences. - 0044-7447. ; 33:7, s. 418-435
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Forskningsöversikt (refereegranskat)abstract
- Environmental manipulation experiments showed that species respond individualistically to each environmental-change variable. The greatest responses of plants were generally to nutrient, particularly nitrogen, addition. Summer warming experiments showed that woody plant responses were dominant and that mosses and lichens became less abundant. Responses to warming were controlled by moisture availability and snow cover. Many invertebrates increased population growth in response to summer warming, as long as desiccation was not induced. CO2 and UV-B enrichment experiments showed that plant and animal responses were small. However, some microorganisms and species of fungi were sensitive to increased UV-B and some intensive mutagenic actions could, perhaps, lead to unexpected epidemic outbreaks. Tundra soil heating, CO 2 enrichment and amendment with mineral nutrients generally accelerated microbial activity. Algae are likely to dominate cyanobacteria in milder climates. Expected increases in winter freeze-thaw cycles leading to ice-crust formation are likely to severely reduce winter survival rate and disrupt the population dynamics of many terrestrial animals. A deeper snow cover is likely to restrict access to winter pastures by reindeer/caribou and their ability to flee from predators while any earlier onset of the snow-free period is likely to stimulate increased plant growth. Initial species responses to climate change might occur at the sub-species level: an Arctic plant or animal species with high genetic/racial diversity has proved an ability to adapt to different environmental conditions in the past and is likely to do so also in the future. Indigenous knowledge, air photographs, satellite images and monitoring show that changes in the distributions of some species are already occurring: Arctic vegetation is becoming more shrubby and more productive, there have been recent changes in the ranges of caribou, and "new" species of insects and birds previously associated with areas south of the treeline have been recorded. In contrast, almost all Arctic breeding bird species are declining and models predict further quite dramatic reductions of the populations of tundra birds due to warming. Species-climate response surface models predict potential future ranges of current Arctic species that are often markedly reduced and displaced northwards in response to warming. In contrast, invertebrates and microorganisms are very likely to quickly expand their ranges northwards into the Arctic.
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| 2. |
- Jonsdottir, Ingibjörg H, 1966, et al.
(författare)
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Muscle contractions induce interleukin-6 mRNA production in rat skeletal muscles.
- 2000
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Ingår i: The Journal of physiology. - 0022-3751. ; 528 Pt 1, s. 157-63
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Tidskriftsartikel (refereegranskat)abstract
- 1. The present study explored the hypothesis that interleukin-6 (IL-6) might be locally produced in response to skeletal muscle contractions and whether the production might reflect the type of muscle contraction performed. Rats were anaesthetized and the calf muscles of one limb were stimulated electrically for concentric or eccentric contractions (4 x 10 contractions with 1 min of rest between the 4 series, 100 Hz). The contralateral muscles served as unstimulated controls. The mRNA levels for IL-6, the glucose transport protein GLUT-4 and beta-actin in the rat muscles (white and red gastrocnemius and soleus) were quantified by quantitative competitive RT-PCR. 2. The IL-6 mRNA level, measured 30 min after the stimulation, increased after both eccentric and concentric contractions and there were no significant differences in IL-6 mRNA levels between the different muscle fibre types. No significant increase in IL-6 mRNA level was seen in the unstimulated contralateral muscle fibres. 3. No increase in GLUT-4 mRNA level was detected, indicating that the increase in IL-6 mRNA level was not due to general changes in transcription. 4. We conclude that IL-6 is locally produced after muscle contraction, with no significant differences between different muscle fibre types. This local production of IL-6 is not due to general changes in transcription, since no changes in the level of GLUT-4 mRNA were found. The fact that increased IL-6 mRNA levels were seen after both concentric and eccentric contractions indicates that the production of IL-6 is not solely due to muscle damage, seen primarily after eccentric exercise.
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| 3. |
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| 4. |
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| 5. |
- Krebs, C. J., et al.
(författare)
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Terrestrial trophic dynamics in the Canadian Arctic
- 2003
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Ingår i: Canadian Journal of Zoology-Revue Canadienne De Zoologie. ; 81, s. 827-843
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Tidskriftsartikel (refereegranskat)abstract
- The Swedish Tundra Northwest Expedition of 1999 visited 17 sites throughout the Canadian Arctic. At 12 sites that were intensively sampled we estimated the standing crop of plants and the densities of herbivores and predators with an array of trapping, visual surveys, and faecal-pellet transects. We developed a trophic-balance model using ECOPATH to integrate these observations and determine the fate of primary and secondary production in these tundra ecosystems, which spanned an 8-fold range of standing crop of plants. We estimated that about 13% of net primary production was consumed by herbivores, while over 70% of small-herbivore production was estimated to flow to predators. Only 9% of large-herbivore production was consumed by predators. Organization of Canadian Arctic ecosystems appears to be more top-down than bottom-up. Net primary production does not seem to be herbivore-limited at any site. This is the first attempt to integrate trophic dynamics over the entire Canadian Arctic.
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| 6. |
- Persson, Anders I., 1973, et al.
(författare)
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Differential regulation of hippocampal progenitor proliferation by opioid receptor antagonists in running and non-running spontaneously hypertensive rats.
- 2004
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Ingår i: The European journal of neuroscience. - : Wiley. - 0953-816X .- 1460-9568. ; 19:7, s. 1847-55
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Tidskriftsartikel (refereegranskat)abstract
- Voluntary running in mice and forced treadmill running in rats have been shown to increase the amount of proliferating cells in the hippocampus. Little is known as yet about the mechanisms involved in these processes. It is well known that the endogenous opioid system is affected during running and other forms of physical exercise. In this study, we evaluated the involvement of the endogenous opioids in the regulation of hippocampal proliferation in non-running and voluntary running rats. Nine days of wheel running was compared with non-running in spontaneously hypertensive rats (SHR), a rat strain known to run voluntarily. On the last 2 days of the experimental period all rats received two daily injections of the opioid receptor antagonists naltrexone or naltrindole together with injections of bromodeoxyuridine to label dividing cells. Brain sections from the running rats showed approximately a five-fold increase in newly generated cells in the hippocampus, and this increase was partly reduced by naltrexone but not by naltrindole. By contrast, both naltrexone and naltrindole increased hippocampal proliferation in non-running rats. In non-running rats the administration of naltrexone decreased corticosterone levels and adrenal gland weights, whereas no significant effects on these parameters could be detected for naltrindole. However, adrenal gland weights were increased in naltrexone- but not in naltrindole-administered running rats. In addition, in voluntary running rats there was a three-fold increase in the hippocampal levels of Met-enkephalin-Arg-Phe compared with non-runners, indicating an increase in opioid activity in the hippocampus during running. These data suggest an involvement of endogenous opioids in the regulation of hippocampal proliferation in non-running rats, probably through hypothalamic-pituitary-adrenal axis modulation. During voluntary running in SHR naltrexone altered hippocampal proliferation via as yet unknown mechanisms.
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| 7. |
- Stenstrom, A., et al.
(författare)
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Genetic variation and clonal diversity in four clonal sedges (Carex) along the Arctic coast of Eurasia
- 2001
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Ingår i: Molecular Ecology. - 0962-1083 .- 1365-294X. ; 10:2, s. 497-513
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Tidskriftsartikel (refereegranskat)abstract
- We studied the structure of genetic variation (at both ramet- and genet-level) and clonal diversity within and among populations in the four closely related arctic clonal sedges Carex bigelowii, C. ensifolia, C. lugens and C. stans by use of allozyme markers. Compared to other sedges and arctic plants, the studied taxa all had high levels of genetic variation, both within populations and taxa. These taxa contained most of the total gene diversity (HT) within populations and a small part of the diversity among populations (GST ranged 0.05-0.43). Carex bigelowii had genetic variation (HS = 0.173, mean for populations) at a comparable level to other outbreeding arctic plants and to other widespread, rhizomatous and mainly outbreeding Carex species. In contrast, C. ensifolia (HS = 0.335), C. lugens (HS = 0.339) and C. stans (HS = 0.294) had within-population variations that were higher than in most other studied Carex species and for arctic plants in general. Genetic variation was not related to any tested environmental variable, but it was lower in areas deglaciated only 10 000 years BP compared to areas deglaciated 60 000 years BP or not glaciated at all during the Weichselian. All the populations were multiclonal, except for two populations of C. stans that were monoclonal. In contrast to genetic variation, clonal diversity decreased with latitude and did not differ between areas with different times of deglaciation. In accordance with previous studies, C. bigelowii and C. lugens were found to be outbreeding, while C. ensifolia and C. stans had mixed mating systems.
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| 8. |
- Stenström, A, et al.
(författare)
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Genetic variation and clonal diversity in four clonal sedges (Carex) along the Arctic coast of Eurasia
- 2001
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Ingår i: Molecular Ecology. - : Wiley. - 0962-1083 .- 1365-294X. ; 10:2, s. 497-513
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Tidskriftsartikel (refereegranskat)abstract
- We studied the structure of genetic variation (at both ramet- and genet-level) and clonal diversity within and among populations in the four closely related arctic clonal sedges Carex bigelowii, C. ensifolia, C. lugens and C. starts by use of allozyme markers. Compared to other sedges and arctic plants, the studied taxa all had high levels of genetic variation, both within populations and taxa. These taxa contained most of the total gene diversity (H-T) within populations and a small part of the diversity among populations (G(ST) ranged 0.05-0.43). Carex bigelowii had genetic variation (H-S = 0.173, mean for populations) at a comparable level to other outbreeding arctic plants and to other widespread, rhizomatous and mainly outbreeding Carex species. In contrast, C. ensifolia (H-S = 0.335), C. lugens (H-S = 0.339) and C. stans (H-S = 0.294) had within-population variations that were higher than in most other studied Carex species and for arctic plants in general. Genetic variation was not related to any tested environmental variable, but it was lower in areas deglaciated only 10 000 years BP compared to areas deglaciated 60 000 years BP or not glaciated at all during the Weichselian. All the populations were multiclonal, except for two populations of C. starts that were monoclonal. In contrast to genetic variation, clonal diversity decreased with latitude and did not differ between areas with different times of deglaciation. In accordance with previous studies, C. bigelowii and C. lugens were found to be outbreeding, while C. ensifolia and C. stans had mixed mating systems.
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