Secondary Chemistry (secondary + chemistry)

Distribution by Scientific Domains

Selected Abstracts

Host shifting by Operophtera brumata into novel environments leads to population differentiation in life-history traits

Adam J. Vanbergen
Abstract., 1. Operophtera brumata L. (Lepidoptera: Geometridae), a polyphagous herbivore usually associated with deciduous trees such as oak Quercus robur L., has expanded its host range to include the evergreen species heather Calluna vulgaris (L.) Hull and, most recently, Sitka spruce Picea sitchensis (Bong.) Carrière. 2. Phenology, morphology, and survival of O. brumata were measured at several life-history stages in populations from the three different host plant communities sampled from a range of geographical locations. The data were used to test for population differences, reflecting the marked differences in host-plant secondary chemistry, growth form, and site factors such as climate. The hypothesis that spruce-feeding populations originated from populations feeding on moorland, commonly sites of coniferous afforestation, was also tested. 3. Altitude, not host plant species, was the major influence on the timing of adult emergence. An effect of insect population independent of altitude was found, implying that additional unidentified factors contribute to this phenological variation. Larval survival and adult size varied between populations reared on different host plant species. Survival of larvae was affected negatively when reared on the novel host plant, Sitka spruce, versus the natal plant (oak or heather) but oak and heather-sourced insects did not differ in survivorship on Sitka spruce. 4. Host range extension into novel environments has resulted in population differentiation to the local climate, demonstrating that host shifts pose challenges to the herbivore population greater than those offered by the host plant alone. The hypothesis that Sitka spruce feeding populations have arisen predominantly from moorland feeding populations was not supported. [source]

Beyond six scents: defining a seventh Thymus vulgaris chemotype new to southern France by ethanol extraction

Ken Keefover-Ring
Abstract The concept of plant chemotype has long been useful to describe secondary chemical phenotypes; however, the idea has practical limitations, especially when applied to ecological questions. This work reports the discovery of a new 1,8-cineole chemotype of Thymus vulgaris from a well-studied area in southern France. Multivariate statistical analysis of ethanol-extracted plant terpenes was used to describe this new chemotype and three others found at the site, and the results are used to discuss the chemotype concept. While the total amount of essential oils among these chemotypes showed no difference, the concentration of the main terpene differed significantly, with the 1,8-cineole and cis -sabinene hydrate chemotypes having the lowest amounts of their respective main components, and the linalool chemotype having the highest. The , -terpinyl acetate chemotype had intermediate levels of its main terpene. A factor analysis revealed four factors which explained almost 89% of the total variation in plant essential oils. Each factor represented a separate chemotype, including a cis -sabinene hydrate, linalool, ,- terpinyl acetate and the new 1,8-cineole chemotype. Although the concept of plant chemotype is still valid, better definitions are important when evaluating the influences of a plant's secondary chemistry on other community members. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Global Change Effects on Plant Chemical Defenses against Insect Herbivores

M. Gabriela Bidart-Bouzat
Abstract This review focuses on individual effects of major global change factors, such as elevated CO2, O3, UV light and temperature, on plant secondary chemistry. These secondary metabolites are well-known for their role in plant defense against insect herbivory. Global change effects on secondary chemicals appear to be plant species-specific and dependent on the chemical type. Even though plant chemical responses induced by these factors are highly variable, there seems to be some specificity in the response to different environmental stressors. For example, even though the production of phenolic compounds is enhanced by both elevated CO2 and UV light levels, the latter appears to primarily increase the concentrations of flavonoids. Likewise, specific phenolic metabolites seem to be induced by O3 but not by other factors, and an increase in volatile organic compounds has been particularly detected under elevated temperature. More information is needed regarding how global change factors influence inducibility of plant chemical defenses as well as how their indirect and direct effects impact insect performance and behavior, herbivory rates and pathogen attack. This knowledge is crucial to better understand how plants and their associated natural enemies will be affected in future changing environments. [source]

Interactions between above- and belowground insect herbivores as mediated by the plant defense system

OIKOS, Issue 3 2003
T. M. Bezemer
Plants are frequently attacked by both above- and belowground arthropod herbivores. Nevertheless, studies rarely consider root and shoot herbivory in conjunction. Here we provide evidence that the root-feeding insect Agriotes lineatus reduces the performance of the foliage feeding insect Spodoptera exigua on cotton plants. In a bioassay, S. exigua larvae were allowed to feed on either undamaged plants, or on plants that had previously been exposed to root herbivory, foliar herbivory, or a combination of both. Previous root herbivory reduced the relative growth rates as well as the food consumption of S. exigua by more than 50% in comparison to larvae feeding on the undamaged controls. We found no effects in the opposite direction, as aboveground herbivory by S. exigua did not affect the relative growth rates of root-feeding A. lineatus. Remarkably, neither did the treatment with foliar herbivory affect the food consumption and relative growth rate of S. exigua in the bioassay. However, this treatment did result in a significant change in the distribution of S. exigua feeding. Plants that had been pre-exposed to foliar herbivory suffered significantly less damage on their young terminal leaves. While plant growth and foliar nitrogen levels were not affected by any of the treatments, we did find significant differences between treatments with respect to the level and distribution of plant defensive chemicals (terpenoids). Exposure to root herbivores resulted in an increase in terpenoid levels in both roots as well as in mature and immature foliage. Foliar damage, on the other hand, resulted in high terpenoid levels in young, terminal leaves only. Our results show that root-feeding herbivores may change the level and distribution of plant defenses aboveground. Our data suggest that the reported interactions between below- and aboveground insect herbivores are mediated by induced changes in plant secondary chemistry. [source]

Coupling Short-Term Changes in Ambient UV-B levels with Induction of UV-Screening Compounds,

Joe H. Sullivan
ABSTRACT A substantial number of studies have been conducted over the last several decades to assess the potential impacts of long-term increases in ultraviolet-B radiation (UV-B between 280 and 320 nm) that will result from continued depletion of stratospheric ozone. However, seasonal changes, tropospheric chemistry and cloudiness are the dominant factors controlling ambient UV-B levels on a short-term or daily basis. The effects of short-term changes in UV-B on plant growth, phytochemistry and physiological processes have received relatively little attention. The USDA UV-B Monitoring and Research Program provides an excellent network of stations that provide an opportunity to monitor long-term changes in solar UV-B radiation and evaluate the responses of plants to short-term variation in UV-B levels on a near-real-time basis. In this study barley (Hordeum vulgare L.) and soybean (Glycine max [L] Merr.) were used as model systems. Emerging seedlings of these species were grown under either near-ambient levels of UV-B or under reduced levels (ca 90% reduction) in the field. Periodic measurements of foliar UV-screening compounds were made on separate groups of seedlings planted at intervals over the growing season during contrasting periods of ambient levels of UV radiation. The levels of UV-screening compounds correlated with UV-B levels in both species and with UV-A in soybean but the sensitivity of the response differed between the two species and among the soybean cultivars. Response differences among species may be related to unique secondary chemistry of each species, so one response estimate or action spectrum may not be appropriate for all species. [source]

Large genetic divergence of new, morphologically similar species of sterile lichens from Europe (Lepraria, Stereocaulaceae, Ascomycota): concordance of DNA sequence data with secondary metabolites

CLADISTICS, Issue 4 2008
Judith Fehrer
Lichenized fungi of the genus Lepraria are known for their paucity of morphological characters. Species identification is therefore largely based on secondary chemistry. We investigated different chemotypes of the morphologically highly similar L. jackii species complex by internal transcribed spacer (ITS) sequencing. In phylogenetic analyses including all available Lepraria species, samples belonging to different chemotypes of the L. jackii agg. corresponded to four highly divergent clusters. While true L. jackii was genetically uniform, the other three clades represented previously unrecognized species. They originated from different major speciation events, and two of them were not closely related to any other species. Assessment of intraspecific genetic variability revealed four different patterns with respect to geographic scale. ITS sequences proved to be the most reliable and distinctive characters for species recognition in the Lepraria jackii complex and were in accordance with chemical and ecogeographic data. Frequent occurrence of long branches, relatively few resolved relationships despite high genetic variability, and the discovery and description of a considerable part of the Lepraria species within the last 10 years suggest that the genus is probably much larger than currently known. The diversification of this asexual group in the potential absence of recombination is discussed. © The Willi Hennig Society 2008. [source]