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  • 1
    Electronic Resource
    Electronic Resource
    A test of the short-term advantage of sexual reproduction (1988)
    [s.l.] : Nature Publishing Group
    Nature 331 (1988), S. 714-716 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Anthoxanthum odoratum, sweet vernal grass, was sampled from a mown field on the Duke University campus, in Durham, North Carolina9'12. In May 1982, both single tillers and several inflorescences of A. odoratum were taken from plants located at 4-metre intervals in a 6 x 5 sample grid in the central ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/331714a0
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  • 2
    Electronic Resource
    Electronic Resource
    Testing the Adaptive Plasticity Hypothesis for Plant Responses to Neighbors (1996)
    Oxford, UK : Blackwell Publishing Ltd
    Plant species biology 11 (1996), S. 0 
    Details
    ISSN: 1442-1984
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract The hypothesis that phenotypic plasticity is adaptive has rarely been tested explicitly. To support this hypothesis, it is necessary to demonstrate that the phenotype induced in each environment experienced by an organism has a high relative fitness in that environment. In plants, phytochrome-mediated responses to the reduced ratio of red: far-red light (R:FR) characteristic of dense vegetation have frequently been assumed to be adaptive. Such “shade avoidance” responses include stem elongation, suppression of branching, reallocation of biomass, and accelerated flowering. Phytochrome-mediated responses to neighbors provide an ideal model system for studying the evolution of adaptive plasticity because the ecological context is clear and the physiological and genetic mechanisms are well studied at the molecular level. Moreover, plant phenotypes are easily manipulated by alteration of the R:FR signal. The shade avoidance hypothesis for adaptive plasticity is supported by studies of mutant and transgenic plants in which normal photomorphogenic responses are disabled, and by field experiments employing phenotypic manipulation in natural populations. Suppression of phytochrome-mediated stem elongation at high density results in decreased fitness, as does constitutive expression of the elongated phenotype at low density. There is also evidence for ecotypic variation in shade avoidance responses. In a common garden, plants from woodland populations of Impatiens capensis are less responsive to R:FR than plants from a nearby open site, suggesting local adaptive differentiation for plastic response to light quality.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1442-1984.1996.tb00109.x
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  • 3
    Electronic Resource
    Electronic Resource
    Genetic variation in defensive chemistry in Plantago lanceolata (Plantaginaceae) and its effect on the specialist herbivore Junonia coenia (Nymphalidae) (1995)
    Springer
    Oecologia 101 (1995), S. 75-85 
    Details
    ISSN: 1432-1939
    Keywords: Cost of defense ; Iridoid glycosides ; Junonia coenia ; Plantago lanceolata ; Verbascoside
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract To examine genetic variation in defensive chemistry within and between natural populations of Plantago lanceolata, we performed a greenhouse experiment using clonal replicates of 15 genotypes from each of two populations, from a mowed lawn and an abandoned hayfield. Replicates of each genotype were harvested for determinations of aboveground biomass and leaf chemical content either at the beginning of the experiment (initial controls), after exposure to herbivory by larvae of Junonia coenia, a specialist on P. lanceolata (herbivory treatment), or at the end of the experiment without exposure to herbivory (final controls). Allocation to the iridoid glycosides aucubin and catalpol and the phenylpropanoid glycoside verbascoside displayed significant genetic variation within and between populations, and differed with leaf age. Significant genotypextreatment interactions indicated genetic variation in response of leaf chemistry to the treatments. There was no evidence for a cost of allocation to chemical defense: genetic correlations within and between chemical pathways and between defensive chemicals and aboveground growth were positive or nonsignificant. Although iridoid glycosides are known to be qualitative feeding stimulants for J. coenia, multiple regression of larval survivorship on leaf chemical content and shoot biomass indicated that larvae had lower survivorship on P. lanceolata ge-notypes with higher concentrations of aucubin in the leaves. Larval survivorship was unaffected by levels of catalpol and verbascoside. Thus, although specialist herbivores may respond to defensive chemicals as qualitative feeding stimulants, they do not necessarily have higher fitness on plant genotypes containing higher concentrations of these chemicals.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00328903
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  • 4
    Electronic Resource
    Electronic Resource
    Paternal and maternal effects on propagule size in Anthoxanthum odoratum (1986)
    Springer
    Oecologia 69 (1986), S. 277-282 
    Details
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Propagules (caryopsis plus glumes) from a diallel cross among eight genotypes of Anthoxanthum odoratum were weighed to asses the relative contribution of nuclear, reciprocal, and environmental effects to propagule size. Maternal reciprocal effects were large whereas zygotic nuclear effects were small, although consitently present. There were no interactions between maternal reciprocal and nuclear effects. Environmental effects were large, including environmentally induced maternal effects and within individual variance. These results suggest that response to selection for seed size as a result of sib-competition will be weak, and that seed size differences are relatively unimportant for the maintenance of sexual reproduction in natural populations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00377634
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  • 5
    Electronic Resource
    Electronic Resource
    Effects of genotype, habitat, and seasonal variation on iridoid glycoside content of Plantago lanceolata (Plantaginaceae) and the implications for insect herbivores (1992)
    Springer
    Oecologia 91 (1992), S. 201-207 
    Details
    ISSN: 1432-1939
    Keywords: Seasonal variation ; Iridoid glycosides ; Herbivory ; Plantago ; Genotype x environment interactions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary We investigated the effects of genotype, habitat, and seasonal variation on production of the iridoid glycosides, aucubin and catalpol, in leaves of the common weed Plantago lanceolata. Two genotypes, one each from a lawn and an adjacent abandoned hayfield population, were clonally replicated in the greenhouse, and then planted back into the two habitats. One quarter of the plants from each treatment were harvested on each of four dates, at approximately two-week intervals. Over the course of the growing season, and in both habitats, we found a significant increase in the concentration of both aucubin and catalpol in P. lanceolata leaves. The genotypes differed in their response to environmental variation, both in time and between sites, as indicated by significant genotype x date and genotype x site interactions. Early in the season, habitat (lawn or field) had a greater effect on iridoid glycoside concentration than did plant genotype, but later in the season, plant genotype was more influential in determining the iridoid glycoside concentration. Thus, the relative palatability of Plantago genotypes to specialist and generalist herbivores may vary in time and space.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00317784
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  • 6
    Electronic Resource
    Electronic Resource
    Propagule size, dispersal ability, and seedling performance in Asclepias syriaca (1985)
    Springer
    Oecologia 67 (1985), S. 372-379 
    Details
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Using the propagules of common milkweed (Asclepias syriaca L.) we tested the predictions that decreasing size may increase dispersal ability, but also decrease the probability of seedling success, of wind-dispersed seeds. In 1982 and 1983 we released seeds from four milkweed clones at two heights in an open field and measured their dispersal distances. In the laboratory we measured falling times in a dead air space, seed mass and area, and coma mass and length of the same seeds. The seeds were later planted in a greenhouse and germination, mortality, and seedling dry mass were recorded. Seed mass was negatively correlated with dispersal distance in 1982, but not in 1983 under highly variable wind conditions. Coma mass/seed mass ratio was positively correlated with dispersal distance in 1982. During both years seed mass and coma mass/seed mass ratio were highly significantly correlated with falling time in dead air space. However, heavy seeds had superior germination, survivorship, and seedling mass at harvest, and seeds that germinated fell faster in dead air than those that did not. We found substantial variation in seed morphology both among clones and among pods within clones. Propagule falling times in dead air and (in 1982) dispersal distances in the field also differed significantly among clones and pods. The potential therefore exists for differential dispersal and establishment of milkweed genotypes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00384943
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  • 7
    Electronic Resource
    Electronic Resource
    Flowering plant density and pollinator visitation in Senecio (1983)
    Springer
    Oecologia 60 (1983), S. 97-102 
    Details
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary It has commonly been assumed that pollinator energy intake increases with flowering plant density, and visitation to flowers should therefore be higher in denser stands. I therefore investigated the relationship between flight distance and flight time for bumblebees and butterflies foraging on Senecio integerrimus and S. crassulus in the Colorado Rocky Mountains. I also compared patterns of pollinator visitation and seed set in two adjacent 15x 15 m plots in a population of S. integerrimus; one plot was experimentally thinned of flowering stalks, while the other was left at natural density. Mean flight distance had no effect on mean flight time or the number of florets or heads visited per unit time. There were no significant differences between the two plots in the rate at which plants received visits, although visitation rates varied through the season, with greatest activity at peak flowering. Pollinators were more selective in their visits to plants in the high-density plot, however. Bumblebee-visited plants in the dense plot had a lower variance in stalk height than the plant population average, while butterfly-visited plants in the dense plot had more heads than the population average. Plant density had no effect on number of heads visited per plant, but number of heads visited by bumblebees was correlated with number of heads per plant. Efficiency of visitation (percentage of flowering heads visited), declined with inflorescence size. Flowering plant density had no effect on seed production, and inflorescence size did not affect the percentage of florets setting seed. In Senecio, flowering phenology patterns and differences among pollinators in foraging behavior may have more important consequences for seed set and gene flow patterns than plant density or plant size.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00379326
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  • 8
    Electronic Resource
    Electronic Resource
    Sexual advantage (1989)
    [s.l.] : Nature Publishing Group
    Nature 337 (1989), S. 413-414 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] KELLEY ET AL. REPLY- Shaanker and Ganeshaiah seem to have misunder-stood the purpose of our experiment. We intended to test the short-term advantage of sexual versus asexual reproduction, and not the advantage of seed versus vegeta-tive propagation. Hence, we were inter-ested in measuring ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/337413c0
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  • 9
    Electronic Resource
    Electronic Resource
    Genetic mechanisms and evolutionary significance of natural variation in Arabidopsis (2006)
    [s.l.] : Nature Publishing Group
    Nature 441 (2006), S. 947-952 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Genomic studies of natural variation in model organisms provide a bridge between molecular analyses of gene function and evolutionary investigations of adaptation and natural selection. In the model plant species Arabidopsis thaliana, recent studies of natural variation have led to the ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/nature04878
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