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- Hargeby, Anders, et al.
(författare)
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Habitat-specific pigmentation in a freshwater isopod : Adaptive evolution over a small spatiotemporal scale
- 2004
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Ingår i: Evolution. - : Wiley. - 0014-3820 .- 1558-5646. ; 58:1, s. 81-94
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Tidskriftsartikel (refereegranskat)abstract
- Pigmentation in the freshwater isopod Asellus aquaticus (Crustacea) differed between habitats in two Swedish lakes. In both lakes, isopods had lighter pigmentation in stands of submerged vegetation, consisting of stoneworts (Chara spp.), than in nearby stands of reed (Phragmites australis). Experimental crossings of light and dark isopods in a common environment showed that pigmentation had a genetic basis and that genetic variance was additive. Environmental effects of diet or chromatophore adjustment to the background had minor influence on pigmentation, as shown by laboratory rearing of isopods on stonewort or reed substrates, as well as analyses of stable isotope ratios for isopods collected in the field. In both study lakes, the average phenotype became lighter with time (across generations) in recently established stonewort stands. Taken together, these results indicate that altered phenotype pigmentation result from evolutionary responses to local differences in natural selection. Based on the assumption of two generations per year, the evolutionary rate of change in pigmentationwas 0.08 standard deviations per generation (haldanes) over 20 generations in one lake and 0.22 haldanes over two generations in the other lake. This genetic change occurred during an episode of population growth in a novel habitat, a situation known to promote adaptive evolution. In addition, stonewort stands constitute large and persistent patches, characteristics that tend to preserve local adaptations produced by natural selection. Results from studies on selective forces behind the adaptivedivergence suggest that selective predation from visually oriented predators is a possible selective agent. We found no indications of phenotype-specificmovements between habitats. Mating within stonewort stands was random with respect to pigmentation, but on a whole-lake scale it is likely that mating is assortative, as a result of local differences in phenotype distribution.
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| 2. |
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| 3. |
- Andersson, Jonas, 1975-
(författare)
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Ion recombination in liquid ionization chambers : development of an experimental method to quantify general recombination
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- An experimental method (the two-dose-rate method) for the correction of general recombination losses in liquid ionization chambers has been developed and employed in experiments with different liquids and radiation qualities. The method is based on a disassociation of initial and general recombination, since an ionized liquid is simultaneously affected by both of these processes.The two-dose-rate method has been compared to an existing method for general recombination correction for liquid ionization chambers, and has been found to be the most robust method presently available.The soundness of modelling general recombination in liquids on existing theory for gases has been evaluated, and experiments indicate that the process of general recombination is similar in a gas and a liquid. It is thus reasonable to employ theory for gases in the two-dose-rate method to achieve experimental corrections for general recombination in liquids. There are uncertainties in the disassociation of initial and general recombination in the two-dose-rate method for low applied voltages, where initial recombination has been found to cause deviating results for different liquids and radiation qualities.Sensitivity to ambient electric fields has been identified in the microLion liquid ionization chamber (PTW, Germany). Experimental data may thus be perturbed if measurements are conducted in the presence of ambient electric fields, and the sensitivity has been found to increase with an increase in the applied voltage. This can prove to be experimentally limiting since general recombination may be too severe for accurate corrections if the applied voltage is low.
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| 4. |
- Forsman, Anders, et al.
(författare)
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Fitness benefits of diverse offspring in pygmy grasshoppers
- 2007
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Ingår i: Evolutionary Ecology Research. ; 9:8, s. 1305-1318
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Tidskriftsartikel (refereegranskat)abstract
- Question: Do females obtain fitness benefits from an increase in offspring diversity?Hypotheses: Polyandry increases offspring diversity within a clutch. Increased offspring diversity will reduce competition among siblings (manifested as increased mean survival in more diverse families) and the probability that all offspring might be ill-suited to future conditions (manifested as lower variance in survival in diverse families).Organisms: Pygmy grasshoppers, Tetrix subulata and Tetrix: undulata, that are polymorphic for colour pattern.Field site: South-central Sweden.Methods: We varied the number of mates provided to colour polymorphic pygmy grasshoppers. We reared families in either warm or cold conditions using a split-brood design.Conclusions: The colour morph diversity of broods increased with the number of experimentally provided mates. Colour morphs represent alternative strategies that differ in body size, physiology, behaviour, and life history. Survival increased with increasing sibling diversity, supporting the hypothesis that different morphs avoid competition by using different subsets of available resources. Homogeneous families (in which all siblings belong to the same or only a few colour morphs) varied more in survival than did families with diverse siblings, supporting the hypothesis that morphs vary in their ability to cope with and utilize different resources.
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| 5. |
- Källman, Hans-Erik, et al.
(författare)
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Source modeling for Monte Carlo dose calculation of CT examinations with a radiotherapy treatment planning system
- 2016
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Ingår i: Medical physics (Lancaster). - : Wiley. - 0094-2405. ; 43:11, s. 6118-6128
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Tidskriftsartikel (refereegranskat)abstract
- Purpose:Radiation dose to patients undergoing examinations with Multislice Computed Tomography (MSCT) as well as Cone Beam Computed Tomography (CBCT) is a matter of concern. Risk management could benefit from efficient replace rational dose calculation tools. The paper aims to verify MSCT dose calculations using a Treatment Planning System (TPS) for radiotherapy and to evaluate four different variations of bow-tie filter characterizations for the beam model used in the dose calculations.Methods:A TPS (RayStation™, RaySearch Laboratories, Stockholm, Sweden) was configured to calculate dose from a MSCT (GE Healthcare, Wauwatosa, WI, USA). The x-ray beam was characterized in a stationary position the by measurements of the Half-Value Layer (HVL) in aluminum and kerma along the principal axes of the isocenter plane perpendicular to the beam. A Monte Carlo source model for the dose calculation was applied with four different variations on the beam-shaping bow-tie filter, taking into account the different degrees of HVL information but reconstructing the measured kerma distribution after the bow-tie filter by adjusting the photon sampling function. The resulting dose calculations were verified by comparison with measurements in solid water as well as in an anthropomorphic phantom.Results:The calculated depth dose in solid water as well as the relative dose profiles was in agreement with the corresponding measured values. Doses calculated in the anthropomorphic phantom in the range 26–55 mGy agreed with the corresponding thermo luminescence dosimeter (TLD) measurements. Deviations between measurements and calculations were of the order of the measurement uncertainties. There was no significant difference between the different variations on the bow-tie filter modeling.Conclusions:Under the assumption that the calculated kerma after the bow-tie filter replicates the measured kerma, the central specification of the HVL of the x-ray beam together with the kerma distribution can be used to characterize the beam. Thus, within the limits of the study, a flat bow-tie filter with an HVL specified by the vendor suffices to calculate the dose distribution. The TPS could be successfully configured to replicate the beam movement and intensity modulation of a spiral scan with dose modulation, on the basis of the specifications available in the metadata of the digital images and the log file of the CT.
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