Publications chemical defenses

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Bird ecology - Insect ecology - Plant ecology - Dendroecology - Plants chemical defenses - Deer biology - Synthesis

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Publications - Plants chemical defenses

G. Vourc’h, J. Russell, J.-L. Martin, Dominique Gillon, 2003, Short term effect of defoliation on terpene content in Thuja plicata, Ecoscience, Vol. 10 (2) 2003) 161:167 – PDF Abstract: Insect herbivory or mechanical wounding in conifers can induce monoterpene biosynthesis. Low risk of herbivory, coupled with low availability of resources, is hypothesized to favour induced responses and to decrease constitutive defences. We studied the response to defoliation in western redcedar (Thuya plicata) from two regions: the Haida Gwaii archipelago, where mammalian herbivores were lacking until black-tailed deer were introduced at the end of the 19^th century and previous work indicated that trees were less defended, and the north coast mainland (British Columbia, Canada). We predicted that higher induced defences in the island population would compensate for reduced constitutive defences. We used one- and two-year-old nursery-grown seedlings to test 1) whether defoliation would cause a short term chemical response in island western redcedar and 2) whether mainland western redcedars that have always been exposed to large mammalian herbivores respond differently. The concentration in monoterpene and diterpene did not vary significantly in response to defoliation over the 5-day period analyzed regardless of the defoliation intensity or the plant’s origin.
Gwenaël Vourc’h, Bruno Vila, Dominique Gillon, José Escarré, Frédéric Guibal, Hervé Fritz, Thomas P. Clausen and Jean-Louis Martin, 2002, Disentangling the causes of damage variation by deer browsing on young Thuja plicata, OIKOS 98: 271–283, 2002 – PDF Abstract: Long-lived trees experience different levels of damage due to mammalian herbivores. To untangle the mechanisms that underlie this variation, we combined chemical with dendrochronological analyses to study variation in browsing on Western redcedars (Thuja plicata) on Haida Gwaii (British Columbia, Canada). Since the last glaciation, Haida Gwaii forests had lacked large herbivore browser until Sitka black-tailed deer (Odocoileus hemionus sitkensis) were introduced at the beginning of the 20th century. Dendrochronology yielded information on radial growth and plant annual responses to environmental stresses including herbivory. Secondary metabolite content and plant nutritional quality provided insights into proximate causes of food choices made by herbivores. We sampled lightly- and heavily-browsed young trees at four sites: three clear-cut sites with high browsing pressure and one old-growth forest site where browsing pressure had, until recently, been lower. Heavily-browsed young trees had lower concentrations of secondary metabolites and were of lower nutritive value than lightly-browsed trees at all sites. Under high browsing pressure, tree growth patterns suggested that all young trees were initially severely browsed until some trees, currently scored as lightly-browsed, started to escape deer. At the old-growth site, both lightly- and heavily-browsed trees tended to have lower overall average secondary metabolite concentrations than those of all other sites, a trend possibly related to greater canopy closure. Lightly-browsed trees were older than heavilybrowsed ones which resulted, during the period of lower browsing pressure, in higher growth rate and a same pattern of change in growth from one year to the next year. This suggests that, under low browsing pressure, selection of young trees related to chemical defense was weak and that growth differences due to other factors than browsing could be expressed. Under strong browsing pressure, however, all young trees had equally low growth rates until trees with better genetic potential to produce effective defenses were able to escape deer. This suggests that selection by deer could occur on a long-lived tree.
Gwenaël Vourc’h, Michel de Garine-Wichatitsky, Alice Labbé, Dimitri Rosolowski, Jean-Louis Martin, Hervé Fritz, 2002, Monoterpene effect on feeding choice by deer, Journal of Chemical Ecology, Vol. 28, No. 12, December 2002 (°C 2002) – PDF Abstract: A previous study showed that Sitka black-tailed deer (Odocoileus hemionus sitkensis) consumption was negatively correlated with monoterpene content in western redcedar (Thuja plicata). To test whether these monoterpenes were deterrent to Sitka black-tailed deer, we performed feeding choice experiments with four hydrocarbon (sabinene, myrcene, β-pinene, and d+ l-limonene) and one oxygenated (β -thujone) monoterpene solution at their highest natural concentration in western redcedar foliage. To test whether deer response was species specific, we ran similar experiments on European roe deer (Capreolus capreolus) and rusa deer (Cervus timorensis russa). In all experiments, monoterpenes were repellent. Solutions with β -thujone, the major monoterpene in redcedar leaves, were the most repellent of the solutions tested. We then analyzed how black-tailed and roe deer responded to (1) an increase in concentration of the monoterpenes with the weakest repellent effects (hydrocarbon monoterpenes) and (2) a decrease in concentration of the monoterpene with strongest effect (β -thujone). Repellency tended to increase with concentration for hydrocarbon monoterpenes, but remained strong for β -thujone. As wild deer regularly feed on plants containing monoterpenes, this raises the question as to how the animals deal with these molecules.
G. Vourc’h, J. Russell, and J.-L. Martin, 2002, Linking Deer Browsing andTerpene Production Among Genetic Identities in Chamaecyparis nootkatensis and Thuja plicata (Cupressaceae), The Journal of Heredity 2002:93(5) 370:376 - PDF Abstract: To investigate whether differential herbivore browsing reflects genetic variation in plant defense expression, variation in needle terpenes and damage caused by black-tailed deer (Odocoileus hemionus) was analyzed on yellow-cedar (Chamaecyparis nootkatensis) and western redcedar (Thuja plicata). In a 100-genet yellowcedar population, three genets that were heavily browsed and had extremely low levels of monoterpenes (0–0.36% dry matter), sesquiterpenes, and diterpenes were compared to unbrowsed genets (0.85–3.83% monoterpenes in dry matter). These differences were maintained in individuals protected from browsing, suggesting genetically based variation in constitutive terpene production. In western redcedar, heavily browsed trees had significantly lower total monoterpene concentrations (1.69% dry matter) than lightly browsed trees (3.32% dry matter). One heavily browsed tree expressed no monoterpenes. No differences were found for diterpenes. In both species, the genotypes with extremely low monoterpene concentrations came from the same penpollinated families.
Bruno Vila, Gwenaël Vourc’h, Dominique Gillon, Jean-Louis Martin, Frédéric Guibal, 2002, Is escaping deer browse just a matter of time in Picea sitchensis? A chemical and dendroecological approach, Trees (2002) 16:488–496 – PDF Abstract: We combined chemical and dendroecological analyses to understand the mechanisms that are involved in escaping deer browse by young Sitka spruce (Picea sitchensis) exposed to browsing by Sitka black-tailed deer (Odocoileus hemionus sitchensis) on Haida Gwaii (British Columbia, Canada). We compared chemical defences (terpenes), nutritive compounds (nitrogen, non-structural constituents, cellulose, and lignin), as well as age and radial growth of two young spruce categories growing side by side: (1) stunted spruces that were heavily browsed, shorter than the browse line, and (2) escaped spruces that were taller than the browse line but still browsed below the browse line. Escaped and stunted spruces did not differ in terpene concentrations, or in nutritive compound contents, suggesting that they had similar palatability. Escaped spruces were older that stunted spruces. Stunted and escaped trees had similar slow growth when young, suggesting no difference in initial browsing between the two spruce categories. For escaped spruce, there was a dramatic increase in radial growth at about 12–13 years old, suggesting that the apex of the trees had escaped deer browse. Because the two categories of spruces were equally accessible and did not differ in chemical defences or in nutritive compounds, and because escaped spruces were older than stunted trees and had a similar slow radial growth in their first 12–13 years, we conclude that morphological differences between stunted and escaped browsed trees are due to age and that it is only a matter of time before spruce escape deer on Haida Gwaii.
Gwenaël Vourc’h, Jean-Louis Martin, Patrick Duncan, José Escarré, Thomas P. Clausen, 2001, Defensive adaptations of Thuja plicata to ungulate browsing: a comparative study between mainland and island populations, Oecologia (2001) 126:84–93 – PDF Abstract: Forests 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. We used the first two plant categories to test the hypothesis that plants that evolve under low herbivory levels have lower anti-herbivore defences. We used saplings to study the consequences of the dramatic increase in browsing on HG. During food experiments, deer preferred HG seedlings and old tree branches compared to those from the mainland. Total monoterpene concentrations were much higher than diterpene concentrations in all plant categories. Within plant categories, multivariate analysis showed that terpene profiles differed significantly between HG and mainland red cedars: HG seedlings and old trees had lower monoterpene levels. These results suggest that some monoterpenes may be determinants of deer food choice and that the defences of HG plants are less effective than those of mainland plants. The deer used branches from HG and mainland saplings indiscriminately. However, terpene profiles differed significantly between HG and mainland saplings, with multivariate analysis suggesting a higher defensive response in browsed HG saplings. Monoterpene profiles were different in lightly and heavily browsed saplings from HG, suggesting that under the current browsing regime, individuals with the greatest constitutive defences, or with greatest potential for induced defences, grow better and are selected on HG.

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