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Godschalx, Adrienne

Nom
Godschalx, Adrienne
Affiliation principale
Fonction
Ancien.ne collaborateur.trice
Identifiants
https://libra.unine.ch/handle/123456789/30731

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  • Publication
    Accès libre
    Is protection against florivory consistent with the optimal defense hypothesis?
    (2016-1-28)
    Godschalx, Adrienne 
    ;
    Stady, Lauren
    ;
    Watzig, Benjamin
    ;
    Ballhorn, Daniel
    Plant defense traits require resources and energy that plants may otherwise use for growth and reproduction. In order to most efficiently protect plant tissues from herbivory, one widely accepted assumption of the optimal defense hypothesis states that plants protect tissues most relevant to fitness. Reproductive organs directly determining plant fitness, including flowers and immature fruit, as well as young, productive leaf tissue thus should be particularly well-defended. To test this hypothesis, we quantified the cyanogenic potential (HCNp)—a direct, chemical defense—systemically expressed in vegetative and reproductive organs in lima bean (Phaseolus lunatus), and we tested susceptibility of these organs in bioassays with a generalist insect herbivore, the Large Yellow Underwing (Noctuidae: Noctua pronuba). To determine the actual impact of either florivory (herbivory on flowers) or folivory on seed production as a measure of maternal fitness, we removed varying percentages of total flowers or young leaf tissue and quantified developing fruit, seeds, and seed viability. Results We found extremely low HCNp in flowers (8.66 ± 2.19 μmol CN− g−1 FW in young, white flowers, 6.23 ± 1.25 μmol CN− g−1 FW in mature, yellow flowers) and in pods (ranging from 32.05 ± 7.08 to 0.09 ± 0.08 μmol CN− g−1 FW in young to mature pods, respectively) whereas young leaves showed high levels of defense (67.35 ± 3.15 μmol CN− g−1 FW). Correspondingly, herbivores consumed more flowers than any other tissue, which, when taken alone, appears to contradict the optimal defense hypothesis. However, experimentally removing flowers did not significantly impact fitness, while leaf tissue removal significantly reduced production of viable seeds. Conclusions Even though flowers were the least defended and most consumed, our results support the optimal defense hypothesis due to i) the lack of flower removal effects on fitness and ii) the high defense investment in young leaves, which have high consequences for fitness. These data highlight the importance of considering plant defense interactions from multiple angles; interpreting where empirical data fit within any plant defense hypothesis requires understanding the fitness consequences associated with the observed defense pattern.
  • Publication
    Accès libre
    Chemical defense lowers plant competitiveness
    (2014-8-31)
    Ballhorn, Daniel
    ;
    Godschalx, Adrienne 
    ;
    Smart, Savannah
    ;
    Kautz, Stefanie
    ;
    Schädler, Martin
    Both plant competition and plant defense affect biodiversity and food web dynamics and are central themes in ecology research. The evolutionary pressures determining plant allocation toward defense or competition are not well understood. According to the growth–differentiation balance hypothesis (GDB), the relative importance of herbivory and competition have led to the evolution of plant allocation patterns, with herbivore pressure leading to increased differentiated tissues (defensive traits), and competition pressure leading to resource investment towards cellular division and elongation (growth-related traits). Here, we tested the GDB hypothesis by assessing the competitive response of lima bean (Phaseolus lunatus) plants with quantitatively different levels of cyanogenesis—a constitutive direct, nitrogen-based defense against herbivores. We used high (HC) and low cyanogenic (LC) genotypes in different competition treatments (intra-genotypic, inter-genotypic, interspecific), and in the presence or absence of insect herbivores (Mexican bean beetle, Epilachna varivestis) to quantify vegetative and generative plant parameters (above and belowground biomass as well as seed production). Highly defended HC-plants had significantly lower aboveground biomass and seed production than LC-plants when grown in the absence of herbivores implying significant intrinsic costs of plant cyanogenesis. However, the reduced performance of HC- compared to LC-plants was mitigated in the presence of herbivores. The two plant genotypes exhibited fundamentally different responses to various stresses (competition, herbivory). Our study supports the GDB hypothesis by demonstrating that competition and herbivory affect different plant genotypes differentially and contributes to understanding the causes of variation in defense within a single plant species.