Phytochemical interrelationships in the Cornaceae

The distribution of iridoids, ellagitannins, proanthocyanidins and other compounds in the Cornaceae and related families is discussed in relation to the various taxonomic treatments. Analysis of the chemical data indicates that: (a) Benthamia and Cynoxylon are the most primitive sub-genera in Cornus, (b) Corokia possesses a chemical pattern consistent with that of the Cornaceae, but Helwingia might better be elevated to family rank, (c) Alangiaceae, Davidiaceae, Garryaceae and Nyssaceae broadly fall into the same pattern as the Cornaceaa and can be placed in a restricted order, Cornales, which excludes Araliaceae, Umbelliferae and Rhizophoraceae, and (d) the Cornales shows affinities to the Saxifragales and the Dipsacales.     

The genus Comus: Non-flavonoid glucosides as taxonomic markers

Previous proposals for subdivision of the genus Cornus are reviewed. Twenty-seven authenticated Cornus species have been studied for their content of non-flavonoid glucosides. Two distinct groups of taxa can be distinguished on this basis: one, containing a hydroxycyclohexadienone glucoside, along with salidroside, its reduced counterpart, and the second, characterized by containing various iridoid glucosides. The two types of glucosides are apparently mutually exclusive.     

Plant‐mediated effects of soil nitrogen enrichment on a chemically defended specialist herbivore,Calophasia lunula

1. Nitrogen enrichment is an important driver of environmental change. In the present study, plant‐mediated effects of increased nitrogen on a specialist herbivore, Calophasia lunula Hufnagel, which sequesters antirrhinoside, an iridoid glycoside produced by its host plants, were examined. 2. Caterpillars were reared on Linaria dalmatica plants grown under low or high N treatments, and C. lunula performance traits and antirrhinoside levels were measured. Additionally, a bioassay was conducted with predatory ants to examine their response to antirrhinoside. 3. Nitrogen enrichment increased larval biomass and decreased larval antirrhinoside concentrations, but had no effect on plant iridoid glycoside concentrations or larval antirrhinoside content. Thus, differences in larval antirrhinoside concentrations were evidently a consequence of increased larval biomass. Additionally, nitrogen treatment had no effects on pupal performance or defence traits. 4. Bioassay results demonstrated a deterrent effect of antirrhinoside, but additional tests are necessary to evaluate the defensive role of this compound in insects. 5. Surprisingly, this study demonstrated little effect of a six‐fold increase in nitrogen availability on L. dalmatica iridoid glycoside concentrations or sequestration by C. lunula. Moreover, the results suggested that changes in plant primary chemistry were more important than secondary chemistry for this specialist herbivore, and that some insects may be insensitive to N enrichment.     

Enzymatic hydrolysis of plumieride to plumieridine

The hydrolysis of plumieride to form the aglycone plumieridine was catalysed by a commercial preparation of cellulase from Aspergillus niger.     

Physiological mechanisms underlying the costs of chemical defence in Junonia coenia Hu¨bner (Nymphalidae): A gravimetric and quantitative genetic analysis

Several recent studies document that specialist insect phytophages may be less subject to predation than generalists and suggest that hostplant-derived chemical defences may be an important explanation for the predominance of specialized feeding among insect herbivores. The evolution of such chemical defences depends upon both their advantages versus natural enemies and their physiological costs, but data on these costs, particularly genetic data, are few. Here I report the results of an ecological genetic investigation of food use efficiency and allelochemical sequestration in Junonia coenia Hu¨bner (Nymphalidae). I used standard gravimetric techniques to estimate the efficiency of dry matter incorporation and iridoid glycoside sequestration in the larvae of 37 full-sib families fed artificial diets containing trace, low (2%) and high (10%) concentrations of iridoid glycosides. I found a significant reduction in the efficiency of dry matter incorporation on a high iridoid diet that is entirely attributable to reduced digestibility rather than post-digestive toxic effects. Larvae fed high-iridoid diets sequestered them less efficiently, but this difference was due largely to post-digestive effects. Analyses of genetic variation and architecture of dry matter and iridoid budgets reveal substantial genetic variation in both suites of traits, but only chemical defence showed a significant genotype×environment interaction which would be conducive to the evolution of specialization. Neither group of traits showed across-diet trade-offs in the form of negative correlations of family means among diets. Family means correlations of sequestration indices with dry matter indices within diets reveals that chemical defence comes at a cost to growth, but only in the high diet. I also found evidence of specialized physiological machinery for iridoid glycoside processing. These data indicate that even adapted specialists are negatively affected by plant toxins, but in this species, dietary specialization is more likely to result from selection from natural enemies than from hostplant toxins.