Because many secondary metabolites in plants act as defense against herbivores it has been postulated that these compounds have evolved under selective pressure by insect herbivores. One explanation for the within-species variation in metabolite patterns in a particular species is that different populations are under selection by different herbivores. We tested this hypothesis, using Arabidopsis thaliana plants that originated from dune and inland areas. We analyzed Arabidopsis thaliana leaves using NMR spectroscopy and multivariate data analysis. Major differences in chemical composition were found in water-methanol fractions and were due to higher concentrations of sinigrin and fumaric acid in dune plants. Inland plants showed lower levels of glucose. Quantitative analysis of glucosinolates was performed with HPLC. Individual plants and populations demonstrated differences in glucosinolate composition and concentration. In growth chamber experiments, the generalist herbivore, Spodoptera exigua grew significantly better on the inland plants, while the specialist herbivore Plutella xylostella performed equally well on plants of both origins. Aliphatic glucosinolate as well as total glucosinolate concentrations negatively correlated with larval mass of Spodoptera exigua. No significant correlations, however, were found between larval mass of Plutella xylostella and glucosinolates in the leaves. A specialist and a generalist herbivore were responding differently to plant secondary chemistry, as was also found in several other studies. This is an important indication that differences in glucosinolate concentrations among populations may result from differential selection by different guilds of herbivores.

Population dynamics of the annual plant Arabidopsis thaliana (L.) Heynh. were studied in a natural habitat of this species on the coastal dunes of the Netherlands. The main objective was to elucidate factors controlling population dynamics and the relative importance of factors affecting final population density. Permanent plots were established and plants were mapped to obtain data on survival and reproductive performance of each individual, with special attention to herbivore damage. In experimental plots we studied how watering, addition of nutrients, artificial disturbance, and natural herbivores affected survival and growth. Mortality was low during autumn and early winter and high at the time of stem elongation, between February and April. A key factor analysis showed a high correlation between mortality from February to April and total mortality. The specialist weevils Ceutorhyncus atomus and C. contractus (Curculionidae) were identified as the major insect herbivores on A. thaliana, reducing seed production by more than 40 %. These herbivores acted in a plant size-dependent manner, attacking a greater fraction of the fruits on large plants. While mortality rates were not affected by density, fecundity decreased with density, although the effect was small. Adding water reduced mortality in rosette and flowering plant stages. Soil disturbance did not increase seed germination, but did have a significant positive effect on survival of rosette and flowering plants. Seed production of A. thaliana populations varied greatly between years, leading to population fluctuations, with a small role for density-dependent fecundity and plant size-dependent herbivory.

In this study the removal of Cr (VI) from synthetic wastewater was investigated using Acroptilon repens (Russian Knapweed) fl ower powder under various conditions (pH, contact time and initial concentration of Cr). The capacity of chromium adsorption at equilibrium conditions by this biosorbent was increased by adsorbate concentration. The results also showed that the removal effi ciency of Cr (VI) was increased by increasing the contact time. By increasing the initial concentration of Cr (VI) solution, chromium removal was reduced. The suitability of adsorbents and their constants was tested or evaluated with the Langmuir, Freundlich and Temkin isotherms models. The results indicated that the Freundlich and Langmuir models (R 2 > 0.99) gave a better concordance to the adsorption data in comparison with the Temkin equation (R 2 = 0.97). The adsorption of Cr (VI) followed the pseudo-second-order kinetics (R 2 = 0.991). The study showed that Acroptilon repens fl ower powder can be used as an effective lignocellulosic biomaterial and biosorbent for the removal of Cr (VI) from wastewater.

To explore genetic variation in defence against the natural herbivores of Arabidopsis thaliana, we transplanted genotypes between a dune habitat and inland habitat in both of which A. thaliana occurred naturally. In previous years we had observed that the specialist weevils Ceutorhynchus atomus and C. contractus (Curculionidae) fed conspicuously on flowers and fruits of A. thaliana in the dunes, while these weevils were always rare in inland habitats. Taking all plants together, total fruit damage was indeed much higher in our experimental plots in the dune habitat (59.7%) relative to the inland garden habitat (18.9%). Within a habitat, additional differences existed between plants of different origins, pointing to genetic differences in ecologically relevant characters; plants of inland origin flowered a week earlier, grew better and produced more fruits than plants of dune origin. However, plants of inland origin experienced more total fruit damage by the specialist weevils (75.4%) than plants of dune origin (44.0%) when the two types grew side by side in the dune habitat. Escape from herbivory gives dune genotypes an advantage in their native habitat, whereas stronger growth and higher survival gives inland genotypes an edge under garden conditions.

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Large differences exist in flower and fruit herbivory between dune and inland populations of plants of Arabidopsis thaliana (Brassicaceae). Two specialist weevils Ceutorhynchus atomus and C. contractus (Curculionidae) and their larvae are responsible for this pattern in herbivory. We test, by means of a reciprocal transplant experiment, whether these differences reflect environmental influences or genetic variation in plant defense level. All plants suffered more damage after being transplanted to the dune site than after being transplanted to the inland site. Plants of inland origin suffered more flower and fruit herbivory than plants of dune origin when grown at the dune transplant site, but differences were much smaller at the inland site. Both flower damage by adult weevils and fruit damage by their larvae were subject to significant genotype · environment interactions. The observed pattern in herbivory is a strong indication for local adaption of plant defense to the level of herbivory by Ceutorhynchus. In order to identify the mechanism of defense, a quantitative analysis of glucosinolates was performed on the seeds with HPLC. Highly significant differences were found in glucosinolate types and total concentration. These patterns were mainly determined by the origin of the plants (dune or inland) and by a genotype · environment interaction. Herbivory was not significantly correlated to the concentration of glucosinolates in seeds. We therefore analyzed the total metabolic composition of seeds, using NMR spectroscopy and multivariate data analysis. Major differences in chemical composition were found in the water-methanol fractions: more glucosinolate and sucrose in the dune and more fatty acids, lipids and sinapoylmalate in the inland populations. We discuss which of these chemical factors could explain the marked differences in damage between populations.

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