Dr. Karowe's Research
 

Potential REU student projects for the summer of 2006:

At the moment, it's not clear whether I'll be running elevated CO2 chambers this summer, so I'm not sure whether an REU student working with me this summer will be able to conduct research on the effects of elevated CO2 on plant-herbivore interactions. However, I will certainly have other plant-herbivore projects underway this summer. In particular, I'd be happy to work with an REU student who was interested in asking questions like:

  1. Do plant chemical defenses increase when the plant is attacked by an herbivore?
  2. Do the rate and magnitude of increase in plant defenses depend on the quality of the habitat in which the plant is growing? For instance, do plants in higher nitrogen soils respond more rapidly and fully to herbivore attack?
  3. Do increases in plant defenses actually deter herbivory by the attacking herbivore, and/or by other herbivores?
  4. Do specialist and generalist herbivores differ in the ability to induce plant defenses and/or in susceptibility to those defenses?

An REU student would be able to choose from many plant-defensive chemical-herbivore combinations that could be used to address these questions. For instance, a student could use wild mustard, which contains glucosinolates and is fed upon by the cabbage butterfly (a specialist) and the differential grasshopper (a generalist). Or a student could work with aspen, which contains phenolic glycosides and is fed upon by the gypsy moth and forest tent caterpillar (both generalists) and the aspen tortrix moth (a specialist).

Caterpillar of the cabbage butterfly feeding on collard, and an example of a glucosinolate, the typical defensive compound of the mustard family.

Gypsy moth caterpillar feeding on oak, and an example of a phenolic glycoside, the typical defensive compound of aspen trees.

Most likely, the student would gain experience with High-pressure Liquid Chromatography (HPLC), the most widely used method for quantifying plant defenses.

  

 

 

      Long-term studies in Dr. Karowe's laboratory seek to understand 1) the effects of elevated atmospheric carbon dioxide on the nutritional quality and defensive chemistry of host plants, and 2) the consequences of these carbon dioxide-induced changes for the growth, survivorship, and behavior of insect herbivores, parasitoids, and hyperparasitoids.

 Pieris on lantana

    The carbon dioxide content of our atmosphere is expected to double by the end of this century, and my students and I are currently investigating several potential ecological consequences of this global atmospheric change.  Growth under elevated carbon dioxide typically results in increased plant growth, decreased leaf nitrogen and water contents, and increased leaf carbon:nitrogen ratios.  Presumably to compensate for decreased leaf nitrogen content, insect herbivores increase consumption rates but nevertheless usually display reduced survivorship and/or growth.  Thus, it is becoming clear that elevated carbon dioxide is likely to exert substantial direct effects on plants, and may therefore profoundly influence natural ecosystems.

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  Cotesia glomerata laying a clutch of eggs in a Pieris caterpillar. Courtesy of Wageningen Agricultural University.

    Our current research compares these direct effects of elevated carbon dioxide between two contrasting multiple trophic level systems:  one based on crucifer host plants and the other based on legume host plants.  Since a major direct effect of elevated carbon dioxide is dilution of plant nitrogen, the hypothesis underlying this study is that association of host plants with nitrogen-fixing symbionts (legumes) will buffer all trophic levels against the direct effects of elevated carbon dioxide.  

Dave Karowe's open-topped chambers at UMBSchamber close up

    We grow plants at ambient and elevated carbon dioxide at the University of Michigan Biological Station.  We then analyze leaf nutritional quality (nitrogen and water contents and C:N ratio) and secondary chemistry (glucosinolate and alkaloid content) at each carbon dioxide level.  Consequences of elevated carbon dioxide for insect herbivores are identified by measuring larval survivorship, growth, efficiency of food utilization, and oviposition preference among host plants grown under each carbon dioxide level.  We also determine effects on parasitoid and hyperparasitoid survivorship and growth by rearing wasps in caterpillars fed host plants grown under each carbon dioxide level.

         The ultimate goals of this research are to expand our understanding of the direct ecological consequences of elevated carbon dioxide to include the third and fourth trophic levels, and to begin to assess mechanisms responsible for variability among different multiple trophic level systems in their susceptibility to the direct effects of elevated carbon dioxide.

         This work has been supported by grants from the National Science Foundation, the United States Department of Agriculture, and Western Michigan University.
 
 

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