Publications by authors named "Thomas P Clausen"
6-Hydroxycylohex-2-en-1-one (6-HCH) has been reported as a major chemical defense of the winter-dormant internodes of balsam poplar (Populus balsamifera) against feeding by herbivores such as the snowshoe hare (Lepus americanus). We report that the concentration of 6-HCH in the fall internodes is triggered by a single hard frost, and then undergoes an exponential decline through volatilization over the winter that results in barely detectable quantities by early spring. We conclude that the role of 6-HCH in the defense of mature balsam poplar is more complex than simply acting as a toxin.
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- Papyriferic acid (PA) is a triterpene secreted by young birch trees, which helps deter mammals like snowshoe hares from feeding on them.
- Research shows that PA is poorly absorbed in the body and undergoes metabolic transformations, primarily through hydrolysis and hydroxylation.
- PA functions as a potent inhibitor of succinate dehydrogenase (SDH) in various animal species, potentially leading to decreased energy production in gastrointestinal cells, which may trigger nausea and deter herbivory.
Article Synopsis
- Fire has been a key disturbance in boreal America, creating a spatial mosaic that significantly influences the density of snowshoe hares, as different areas have varying amounts of early successional plants due to fire.
- This study supports the idea that fire shapes geographic variations in natural selection, particularly where hare populations are high and have strongly influenced the defense mechanisms of juvenile woody plants like Alaska and white birch.
- The research indicates that there is a transcontinental link between the interactions of fire, hares, and plant defenses, with higher levels of defense toxins found in Alaskan hares compared to those in Wisconsin, suggesting a potential coevolutionary dynamic.
In addition to the free protein amino acid l-tyrosine, the expanding young leaves of Inga laurina accumulate high concentrations of three new depsides, galloyl, m-digalloyl, and m-trigalloyl l-tyrosine (1, 2, and 3). The structures of these compounds were determined on the basis of their spectroscopic properties and through degradation and derivatization experiments. They occur in young leaves at the following dry-weight mass percentages: tyrosine, 10.
View Article and Find Full Text PDFThe growth-differentiation balance hypothesis (GDBH) postulates that variation in resource availability can increase or decrease allocation to secondary metabolism, depending on how growth is affected relative to carbon assimilation. Growth and leaf area of black poplar (Populus nigra) increased substantially in response to increased nutrient availability, while net assimilation rate and photosynthesis were less strongly affected. In response, total phenolic glycoside concentrations declined, which is consistent with GDBH.
View Article and Find Full Text PDFMoponeol A (1) and moponeol B (2) were isolated from Colophospermum mopane along with a mixture of their corresponding aldehydes (3 and 4). These substances are primitive diterpenes that we view as the "missing links" in the biosynthesis of the 9,13-epoxylabdanes. The structures of 1 and 2 were elucidated by a combination of spectra (NMR and MS) of the isolates and their mono-p-bromobenzoyl derivatives.
View Article and Find Full Text PDFForests on the Haida Gwaii (HG) archipelago (British Columbia, Canada) evolved for about 10,000 years in the absence of large-mammal browsing. The introduction of black-tailed deer (Odocoileus hemionus sitkensis) from the mainland prior to 1901 provides an opportunity to evaluate changes in the adaptive defensive responses of plants to herbivory. We compared (1) food choice by deer and (2) chemical defence (terpene concentrations) between HG and mainland red cedars (Thuja plicata) using (1) nursery-grown seedlings never exposed to deer, (2) branches from trees that grew before the introduction of deer ("old trees") and (3) saplings exposed to deer herbivory on the mainland and on HG.
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- Snowshoe hares prefer mature growth-phase internodes of Alaska paper birch over juvenile ones because the latter have low nutritional value.
- The preference can't be explained by inorganic nutrients or basic chemical components but is linked to differences in secondary metabolites.
- Juvenile internodes contain high levels of papyriferic acid, a triterpene that deters snowshoe hares from feeding, making them 25 times more concentrated in juvenile internodes compared to mature ones.