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- Persson, Lennart, et al.
(author)
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Cannibalism in a size-structured population : energy extraction and control
- 2004
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In: Ecological Monographs. - : Wiley. - 0012-9615 .- 1557-7015. ; 74:1, s. 135-157
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Journal article (peer-reviewed)abstract
- Recent size-structured cannibalistic models point to the importance of the energy gain by cannibals and also show that this gain may result in the emergence of giant individuals. We use a combination of a 10-year field study of a perch (Perca fluviatilis) population and quantitative within-season modeling of individual and population-level dynamics to investigate which mechanisms are most likely to drive the dynamics of the studied perch population. We focused on three main aspects to explain observed discrepancies between earlier model predictions and data: (1) introduction of more than one shared resource between cannibals and victims, (2) whether or not several victim age cohorts are necessary to allow giant growth, and (3) the intensity of inter-cohort competition between young-of-the-year (YOY) perch and 1-yr-old perch. At the start of the study period, the perch population was dominated by “stunted” perch individuals, and recruitment of perch to an age of 1-yr-old was negligible. Following a major death in adult perch, strong recruitments of perch to 1-yr-old were thereafter observed for a number of years. As 1-yr-olds these successful recruiters subsequently starved to death due to competition with the new YOY. The few surviving adult perch accelerated substantially in growth and became “giants.” At the end of the study period, the perch population moved back to the situation with stunted individuals. There was a high agreement between observed diets of cannibalistic perch and those predicted by the model for both the stunted and the giant phases. Analyses of growth rates showed that cannibalistic perch could become giants on a diet of YOY perch only, but that a supplement with the second shared resource (macroinvertebrates) was needed to reach the observed sizes. Modeling of growth and diet in the giant phase showed an exploitative competitive effect of YOY perch on 1-yr-old perch, but a restriction in habitat use of 1-yr-old perch had to be assumed to yield the observed growth rate and diet. The resource dynamics of zooplankton and macroinvertebrates were both accurately predicted by the model. Also, YOY perch mortality was accurately predicted and, furthermore, suggested that one of the trawling methods used may underestimate the number of YOY perch when they increase in size. We conclude that the presence of a second shared resource and the restricted habitat use and absence of cannibalistic consumption by 1-yr-old perch individuals are two important mechanisms to explain the discrepancy between model predictions and data. Our results also point to the fact that that the dynamics observed may be explained by complex dynamics not involving the presence of a giant and dwarf cycle.
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- Piispanen, PS, et al.
(author)
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Synthesis and characterization of surface-active compounds derived from cholesterol derivatives and glucose
- 2002
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In: Journal of Surfactants and Detergents (JSD). - 1097-3958 .- 1558-9293. ; 5, s. 345-351
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Journal article (peer-reviewed)abstract
- The synthesis and characterization of surface-active compounds based on various steroid derivatives and glucose are presented. The hydrophobic and hydrophilic parts of the compounds were linked via glucosidic bonds. All compounds were found to have very low water solubility and only limited solubility in various organic solvents. The compounds were investigated according to their ability to interact with an anionic surfactant, sodium dodecylsulfate (SDS), in order to induce a decrease in the critical micelle concentration (CMC) of the surfactants. This synergistic effect was pronounced for cholestanol-6-on-ß-d-glucopyranoside and for cholestan-3,6-diol-ß-d-glucopyranoside. These two compounds lowered the CMC from 8 to 6 and 0.6 mM, respectively, for water solutions of SDS/glucoside with a molar ratio of 92:8. Furthermore, the ability of the compounds to stabilize lipid membranes, in liposomes, at varying concentrations of Ca2+, was studied. The compounds were, as expected, found to induce stabilization similar to that of cholesterol
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- Sennström, Maria B., et al.
(author)
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Human cervical ripening, an inflammatory process mediated by cytokines
- 2000
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In: Molecular Human Reproduction. - : Oxford University Press (OUP). - 1360-9947 .- 1460-2407. ; 6:4, s. 81-375
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Journal article (peer-reviewed)abstract
- An extensive remodelling process, referred to as cervical ripening, takes place in the cervical tissue during pregnancy and labour. It is recognized as softening and dilation of the cervical canal, and starts as a slow process during pregnancy, becoming rapid close to partum. In this study we focus on cytokines as possible mediators of this final remodelling. mRNA levels for interleukin (IL)-8, IL-6 and granulocyte colony-stimulating factor (G-CSF) were upregulated in the ripe postpartum cervical tissue (n = 8) compared to the unripe state (n = 9). Likewise, released cytokine concentrations increased from non-pregnant (n = 11) to the term-pregnant group (n = 13) with a further increase at partum (n = 16). IL-8 concentrations increased 4-fold from non-pregnant to term-pregnant (P<0.01), and a further 10-fold to postpartum state (P<0.0001). Concentrations of IL-6 and G-CSF were similarly increased. Specific IL-8 immunostaining was identified in the epithelia of pregnant cervical tissue (n = 7) and was most pronounced in the epithelia and stroma of postpartum tissue (n = 4). In conclusion, IL-8, IL-6 and G-CSF increase in the human cervix during the ripening process, indicating their important role in the cervical remodelling. These data demonstrate that cervical ripening is similar to an inflammatory process.
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- Wreje, U., et al.
(author)
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Collagen metabolism markers as a reflection of bone and soft tissue turnover during the menstrual cycle and oral contraceptive use
- 2000
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In: Contraception. - : Elsevier. - 0010-7824 .- 1879-0518. ; 61:4, s. 265-270
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Journal article (peer-reviewed)abstract
- Two different groups of women, 23 healthy young adults and 13 women with chronic posterior pelvic pain, were studied before and during use of oral contraceptives (OC). Collagen metabolism markers-here, the amino terminal propeptide of type I procollagen, the carboxy-terminal telopeptide of type I collagen, and the amino-terminal of procollagen type III-as well as hormones and other endocrine factors indicating the balance between androgen expression/anabolism and catabolism of the subjects (testosterone, sex-hormone binding globulin, and insulin-like growth factor I were measured. Type I procollagen, the carboxy-terminal telopeptide of type I collagen, and the amino-terminal of procollagen type III were all significantly decreased during OC use. These findings implicate OC use-induced changes in collagen type I and III turnover. A shift in the anabolic/catabolic balance was also recorded indicating a less anabolic situation during OC use.
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