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- Nygren, Georg H., et al.
(författare)
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Latitudinal body size clines in the butterfly Polyommatus icarus are shaped by gene-environment interactions
- 2008
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Ingår i: Journal of Insect Science. ; 8, s. 47-
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Tidskriftsartikel (refereegranskat)abstract
- The study of latitudinal body size clines can illuminate processes of local adaptation, but there is a need for an increased understanding of the relative roles of genetic variation, environmental effects, and interactions between them, in shaping such geographical patterns. For this reason, we combined an investigation of a museum collection of the common blue butterfly Polyommatus icarus (Rottemburg) (Lycaenidae: Polyommatini) from Sweden with a common-garden experiment in the laboratory, using strains reared from individuals collected from three different latitudes. Sizes of the field-collected butterflies tended to smoothly decrease northwards in a latitudinal cline, but suddenly increase at the latitude where the life cycle changes from two to one generations per year, hence allowing more time for this single generation. Further north, the size of the field-collected butterflies again decreased with latitude (with the exception of the northernmost collection sites). This is in accordance with the "converse Bergmann" pattern and with the "saw-tooth model" suggesting that insect size is shaped by season length and number of generations along latitudinal transects. In contrast, under laboratory conditions with a constant long day-length there was a different pattern, with the butterflies pupating at a higher mass when individuals originated from southern populations under time stress to achieve a second generation. This is indirect evidence for field patterns being shaped by end-of-season cues cutting development short, and also suggests counter-gradient variation, as butterflies from the time-stressed populations over-compensated for decreasing larval development time by increasing their growth rates, thus obtaining higher mass. Hence, we found support for both adaptive phenotypic plasticity and local genetic adaptation, with gene-environment interactions explaining the observed field patterns.
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- Nygren, Georg, 1962-
(författare)
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Latitudinal patterns in butterfly life history and host plant choice
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The central subject in this thesis is adaptation of insect populations to different environments along latitudinal gradients. When latitude decreases, the longer favorable season causes an increase in time available for development. However, predictions are complicated by shifts in voltinism. When a species uses the summer for two generations (bivoltine lifestyle) instead of one, the time for each generation is virtually cut in two halves. For this reason models predict a saw-tooth pattern in development time and size. In herbivorous insects, a related model predicts specialization on plants permitting fast growth when time available for development is short (the voltinism-suitability hypothesis). The hypotheses apply to insects with discrete number of generations per year and I have studied butterflies. Manuscript I is an investigation of size response in the butterfly Polyommatus icarus over a latitudinal shift from univoltinism to bivoltinism. The investigation of wild-caught specimens is supplemented with a laboratory experiment on tree populations originating from above, inside and below this shift. The study confirms the predicted saw-tooth pattern size response to available time in this species. Additionally, the laboratory results reveal so-called counter-gradient variation. The second manuscript focuses on the voltinism-suitability hypothesis, and the model organism is now another butterfly, Polygonia c-album, also the subject for the last two studies. The main result of the second study is that female host plant preference and larval survival show much variation between areas, whereas larval development time and growth rate show little variation. Further, the variation in larval performance and adult preference between the two studied host plants (Salix caprea and Urtica dioica) seems to be best explained by host plant phenology. The study also reveals a possible trade-off in performance on the two studied host plants. The third study is an investigation of the genetics of host plant preference in one population via breeding and selection experiments; and the fourth a study of the genetics of preference differences between geographically separated populations via cross-breeding experiments. The variation in host plant preference within the population seems caused by non-additive autosomal inheritance, perhaps with a small effect of the y-chromosome. The variation between populations is primarily caused by one or more genes on the x-chromosome.
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- Nygren, Mats, et al.
(författare)
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Crystal Structure and Transport Properties of Nickel Containing Germanium Clathrates.
- 2007
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Ingår i: Physical Review B: Condensed Matter and Materials Physics. ; 76:24, s. 245126 (9)-
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Tidskriftsartikel (refereegranskat)abstract
- Four Ba8Ni6-xGe40+x clathrate samples with x = 0-0.6 were synthesized and characterized using conventional and synchrotron x-ray powder diffraction. Thermopower, resistivity, thermal cond., Hall effect, and magnetic susceptibility were measured between 2 and 400 K. To support the interpretation of the phys. property data, d. functional theory calcns. were used to obtain band structures and theor. transport properties for a wide range of transition metal substituted clathrate systems having a fully ordered Ba8TM6Ge40 structure. A systematic dependence on x was found for both the structural and the electronic properties, and the latter varies from p- to n-type properties. Despite relatively low mobilities (H) of the charge carriers in all the samples, the thermoelec. properties of p-type Ba8Ni6-xGe40+x are promising. The p-type samples, with the best thermoelec. properties, have ZT = 0.13 at 400 K, where ZT is the dimensionless thermoelec. figure of merit. It is estd. that p-type samples with lower charge carrier concns. will have improved thermoelec. properties. The effect of transition metal substitution on the thermopower and mobility in clathrates is discussed.
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- Nylin, Sören, 1959-, et al.
(författare)
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Geographical variation in host plant utilization in the comma butterfly: the roles of time constraints and plant phenology
- 2009
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Ingår i: Evolutionary Ecology. - Dordrecht : Springer. - 0269-7653 .- 1573-8477. ; 23, s. 807-825
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Tidskriftsartikel (refereegranskat)abstract
- What is the role of time-constraints in determining geographical variation in the resource use of organisms? One hypothesis concerning phytophagous insects predicts a local narrowing of host plant range at localities where a short development time is important (because an additional generation per season is only just possible), with increased specialization on host plants permitting fast development. To test this hypothesis, populations of the polyphagous comma butterfly (Nymphalidae: Polygonia c-album) from five European areas (localities in Norway, Sweden, England, Belgium and Spain) were sampled and the preferences of laboratory-reared female butterflies were investigated, by a choice test between Salix caprea and the fastest host Urtica dioica. The results suggest that females of both of two northern univoltine populations (time-stressed from Norway and time-relaxed from Sweden) accept the slow host S. caprea to a higher degree than females of more southern populations with partial additional generations (time-stressed). We thus found partial support for the tested hypothesis, but also conflicting results that cast doubt on its broad generality. Moreover, a split-brood investigation on Swedish stock demonstrated that larval performance is similar on S. caprea and U. dioica early in the summer, but that later in the season S. caprea is a much inferior host. This is reflected by a seasonal trend towards specialization on U. dioica and also provides a simpler explanation than the time-constraints theory for avoidance of S. caprea (and other woody hosts) in areas with two or more generations of insects per year, illustrating the importance of plant phenology as a constraint on resource use in phytophagous insects. Absolute and relative larval performance on the two hosts varied little among populations across Europe, but lower survival on S. caprea in the populations most specialized on U. dioica and related plants may be indicative of performance trade-offs.
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