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- Persson Sunde, Erik, et al.
(författare)
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The physical state of water in bacterial spores.
- 2009
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Ingår i: Proceedings of the National Academy of Sciences. - : Proceedings of the National Academy of Sciences. - 1091-6490 .- 0027-8424. ; 106:46, s. 19334-19339
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Tidskriftsartikel (refereegranskat)abstract
- The bacterial spore, the hardiest known life form, can survive in a metabolically dormant state for many years and can withstand high temperatures, radiation, and toxic chemicals. The molecular basis of spore dormancy and resistance is not understood, but the physical state of water in the different spore compartments is thought to play a key role. To characterize this water in situ, we recorded the water 2H and 17O spin relaxation rates in D2O-exchanged Bacillus subtilis spores over a wide frequency range. The data indicate high water mobility throughout the spore, comparable with binary protein–water systems at similar hydration levels. Even in the dense core, the average water rotational correlation time is only 50 ps. Spore dormancy therefore cannot be explained by glass-like quenching of molecular diffusion but may be linked to dehydration-induced conformational changes in key enzymes. The data demonstrate that most spore proteins are rotationally immobilized, which may contribute to heat resistance by preventing heat-denatured proteins from aggregating irreversibly. We also find that the water permeability of the inner membrane is at least 2 orders of magnitude lower than for model membranes, consistent with the reported high degree of lipid immobilization in this membrane and with its proposed role in spore resistance to chemicals that damage DNA. The quantitative results reported here on water mobility and transport provide important clues about the mechanism of spore dormancy and resistance, with relevance to food preservation, disease prevention, and astrobiology.
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- Sunde, Peter, et al.
(författare)
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Combining information from range use and habitat selection: sex-specific spatial responses to habitat fragmentation in tawny owls Strix aluco
- 2006
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Ingår i: Ecography. - : Wiley. - 1600-0587 .- 0906-7590. ; 29:2, s. 152-158
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Tidskriftsartikel (refereegranskat)abstract
- How individuals respond to habitat heterogeneity is usually measured as variation in range size and by ranking the relative importance of habitat types (habitat selection). The combined effect of how individuals incorporate different habitat types in their home ranges and allocate their time budget between them is rarely derived. Additionally, when home range size varies between individuals, habitat selection analyses might be flawed if foraging decisions are based on variation in absolute rather than proportional availability. We investigated the suitability of standard analytical approaches by measuring the spatial responses of tawny owls to habitat fragmentation. These owls inhabited woodland of various sizes, representing a fragmentation gradient from open farmland with small, isolated woodland patches, to continuous woodland within their home ranges. In 17 territories within open farmland, the available area covered by woodland increased with the square root of the area of open land embraced in the home range. The owls did not display functional response in habitat selection, but females selected woodland more strongly than males. Females utilised woodland 10 times more intensively in farmland than in continuous woods, whereas males utilised farmland woods 3.2 times more intensively. Moreover, females in farmland exploited woodland 3.2 times as intensively as males, apparently because of higher travel costs in open areas. Since the extensive variation in intensity of use as a function of total availability was not indicated from the analysis of habitat selection, we suggest that information about intensity of use be more widely used as a supplementary measure of habitat use patterns than appears to be the practice at present.
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- Sunde, Peter
(författare)
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Predators control post-fledging mortality in tawny owls, Strix aluco
- 2005
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Ingår i: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 110:3, s. 461-472
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Tidskriftsartikel (refereegranskat)abstract
- Despite its recognition as an important source of variation in recruitment probability, the ecological processes leading to mortality between fledging and independence are poorly studied. Accordingly, the proximate and ultimate impact of bottom-up (food limitation) and top-down factors (predators, pathogens) for individual survival as well as population productivity is largely unknown in most terrestrial birds. Survival and behaviour of 131 radio-tagged tawny owls (Strix aluco) during the post-fledging dependency period were studied for each of three years with high food abundance and three years of poor food supply in Danish deciduous woods. To identify the effects of food limitation, 32 young received extra food 2-3 weeks prior to fledging, as opposed to 99 young that were fed by their parents only. Thirty-six percent of the young from control broods died between fledging and independence, primarily due to predation from raptors and mammals (predominantly foxes Vulpes vulpes). Predation by mammals occurred within the first few days after fledging, with young leaving the nest at an early age being at particularly high risk. Young that had received extra food as nestlings were also at higher risk of being preyed upon by mammals, possibly because they were easier to locate on their smell. Total mortality risk (control broods) increased with fledging date from 14% in April to > 58% in June due to an increasing raptor predation risk. Individual attributes such as sex, condition, immunocompetence or prevalence of blood parasites did not predict total or cause-specific mortality risk. Survival during the post-fledging dependency period was therefore primarily a function of variation in predation pressures, particularly from raptors. Increasing raptor predation of late broods appears to be an important selective agent for early breeding in the tawny owl.
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