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- D'Hertefeldt, Tina, Universitetslektor, 1965-, et al.
(författare)
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Physiological integration of the clonal plant Carex arenaria and its response to soil-borne pathogens
- 1998
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Ingår i: Oikos. - Chichester : Wiley-Blackwell. - 0030-1299 .- 1600-0706. ; 81:2, s. 229-237
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Tidskriftsartikel (refereegranskat)abstract
- We test the hypothesis that the expansive horizontal clonal growth of Carex arenaria may provide a method of escape from soil-borne pathogens (fungi and nematodes) by growing away from the site of infection. Plants were grown in non-sterilized or sterilized dune sand, i.e., with or without soil-borne pathogens. The effects of soil-borne pathogens were studied on the whole genet, on the mother alone, and on the first primary rhizome. Genets with the mother plant infected produced less total biomass and had less biomass allocated to roots than genets with uninfected mothers. Infected genets had fewer primary rhizomes and lower total rhizome length, but rhizome specific weight or the distance between shoots did not decrease in infected plants. In C. arenaria, uninfected mothers with an infected first primary rhizome produced shorter and fewer rhizomes than uninfected genets. The infected first rhizome continued to grow at the same speed as uninfected rhizomes, probably by support from the uninfected mother plant. However, secondary rhizome branching was affected only by direct exposure to soil pathogens and not by the status of the mother plant. The results provide evidence that clonal growth may facilitate escape from soil-borne pathogens. The rhizome explores a patchy environment by supporting the growth of young tillers when passing pathogenic patches.
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| 2. |
- Dinnétz, Patrik, et al.
(författare)
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Spatial distribution of male sterility in Plantago maritima
- 1998
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Ingår i: Oikos. - : JSTOR. - 0030-1299 .- 1600-0706. ; 81, s. 255-265
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Tidskriftsartikel (refereegranskat)abstract
- Sexual polymorphism in angiosperms can be explained both by the functional responses of male and female function to autogamy and geitonogamy, and by the conflict between the nuclear and cytoplasmic genomes. In predominantly hermaphrodite species, cytoplasmically determined male sterility may persist in a population because of maternal inheritance, i.e, the loss of male function does not change the fitness of the cytoplasmic genome. However, in populations with cytoplasmic male sterility, male fertility is often restored by nuclear genes. Therefore, in populations with genetical substructure, the frequencies of the different sex-morphs will fluctuate depending on the presence of both the male sterile cytoplasms, and of their specific nuclear restorer genes. In Plantagomaritima, we showed that the frequencies of male sterility were highest in regions with the highest population turnover rates and that male sterile individuals were more frequently found in the lower, less dense parts of the meadows. This indicates that male sterile cytoplasms have their highest probabilities to escape their nuclear restorer genes during recolonisation in disturbed regions within populations. We also found that male sterile individuals dispersed their seeds a little bit further than did the hermaphrodites. This can be interpreted as an adaptive response to the local occurrence of nuclear restorer genes.
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| 6. |
- Smith, Henrik G., et al.
(författare)
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Intersexual competition in a polygynous mating system
- 1998
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Ingår i: Oikos. - : JSTOR. - 1600-0706 .- 0030-1299. ; 83:3, s. 484-495
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Tidskriftsartikel (refereegranskat)abstract
- In the facultatively polygynous European starling (Sturnus vulgaris) males attract from one to four mates. Males gain by mating polygynously because they produce more offspring by doing so. This is true also genetically, since polygynous males on average father the same proportion of offspring as monogamous males. However, the marginal benefit of attracting additional mates is negatively affected by extra-pair parentage, which is slightly higher in males' secondary broods. Whereas mating as a secondary female is a better option for floater females than either not reproducing at all or reproducing as a brood parasite, already mated females suffer a cost when their mates attract additional mates. This is because they have to share the parental care provided by the male. Males divide parental investment primarily in relation to the timing of the broods produced by their females, investing mainly in the earliest brood. Male parentage has little effect on male care. Already mated females use aggression to prevent floater females to establish a pair-bond with their mates. The mating system in the starling results from the differing interests of males and females. To be able to construct models predicting when a particular mating system should be expected, more has to be learnt about the costs of male mate attraction and nest defence behaviour and female aggression.
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| 7. |
- Tannerfeldt, Magnus, et al.
(författare)
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Fluctuating resources and the evolution of litter size in the arctic fox
- 1998
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Ingår i: Oikos. - : Blackwell. - 0030-1299 .- 1600-0706. ; 83:3, s. 545-559
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Tidskriftsartikel (refereegranskat)abstract
- Fluctuations in essential resources cause a strong selection pressure on the ability to adjust parental investment accordingly. In the dog family, Canidae, variance in female prebirth investment is adjusted by litter size. The arctic fox, Alopex lagopus, is a small canid living on the northern tundras of the world. It has the largest known litter size in the order Carnivora. up to 18 young, and litter size is highly variable. We have analysed data From arctic fox populations throughout the species circumpolar range. In some areas, arctic foxes feed on strongly fluctuating populations of small rodents. In contrast, they have more stable food resources at bird cliffs and along coast lines. Food availability determines arctic fos litter and population sizes. A comparison between fluctuating and stable arctic fox populations showed that fluctuations are associated with large litter sizes. There were significant differences in litter size means, maxima and variances, as well as in placental scar count means. We have discussed five hypotheses on the determination of variation in litter size: one energetic, one genetic (based on density variation), one diet-determined, one based on reproductive allocation and one based on differences in reaction norms. Our findings suggest that litter size in the arctic fox is determined by the combined effect of immediate resource levels and the degree of resource predictability. We describe reaction norms that suggest how litter sizes result from adaptive plasticity within each of two genetic strategies where, according to the jackpot hypothesis, populations with unpredictable food resources generally have larger litter sizes. Within each genetic strategy, or reaction norm, litter sizes are adjusted through a number of plastic trails. These traits are influenced by nutritional limitations and include reduced ovulation rates, prenatal losses, and litter size reduction during the lactation period.
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