Variation in leaf resin composition between parent tree and progeny in Hymenaea: Implications for herbivory in the humid tropics

Variation in the sesquiterpene hydrocarbon leaf resins in the tropical leguminous genus Hymenaea is compared between parent tree, seedling and sapling progeny. Relatively large discrete quantitative variation in the leaf resins, known experimentally to display little phenotypic plasticity, has been classified into Compositional Types. Differences in Compositional Types in the leaves between parent tree and their seedling and sapling progeny are more pronounced in rain forest and related eocystems than in savanna and dry forests. A model is presented in which it is suggested that this variation in leaf resin may play an important role in defence against lepidopteran herbivores and thus also in seedling establishment under Hymenaea parent trees in rain forest and related ecosystems.     

Sesquiterpene Deterrence of a Leaf-Tying Lepidopteran, Stenoma ferrocanella, on Hymenaea stigonocarpa in Central Brazil

Study of two populations of Hymenaea stigonocarpa in the central Brazilian cerrado (savanna/woodland) shows attack by a leaf-tying lepidopteran, Steoma ferrocanella, occurred after inferred peak concentration (% of leaf dry wt) of sesquiterpene leaf resins during leaf development. Also a highly statistically significant relationship existed between leaf-tier attack and level of caryophyllene in one population and γ-muurolene in the other population. The data from one population are consistent with laboratory experiments demonstrating highly significant dose-dependent effects of caryophyllene in Hymenaea leaf resin on mortaility of the lepidopteren Spodoptera exigua. Results from both populations support other evidence that changes in the amount of single terpenes in the mixture constituting the resin may have significant antiherbivore effects and, concomitantly, that herbivory may be a source of some of the leaf resin variation.     

Inhibitory effects of Hymenaea and Copaifera leaf resins on the leaf fungus, Pestalotia subcuticularis

Leaf resins in the leguminous genera Hymenaea and Copaifera may play a role in restricting infection by the associated leaf fungus, Pestalotia. We tested this hypothesis by assessing growth of the geographically widespread Pestalotia subcuticularis presented with different compositions of resins. Leaf resins of Hymenaea and Copaifera are composed of the same suite of sesquiterpene hydrocarbons, but these vary quantitatively to form discrete compositional patterns among individuals and populations. Leaf resins may also contain sesquiterpene oxides; caryophyllene oxide, which may have been formed from the caryophyllene precursor common in these resins, inhibited fungal growth in vitro.     

Quantitative variation in leaf pocket resin composition in Hymenaea courbaril

Leaf pocket resin sesquiterpenes have been quantitatively analyzed in 22 geographic populations of the widespread Hymenaea courbaril. Highly stable quantitative resin composition in Meso-American populations of H. courbaril contrasts with greater variability in several South American populations. In some of the latter, bimodality in quantitative content of several correlated sesquiterpenes results in overall resin compositional relationships of two or three distinct types. Variance-weighted similarity coefficients between all populational pairs are single-linkage clustered to visualize chemical relationships.     

Vegetative growth and leaf resin composition in Hymenaea courbaril under photoperiodic extremes

Seedlings from five geographic populations of the widespread Hymenaea courbaril were grown for one year under two extremes of photoperiod. The short photoperiod treatment consisted of 8 hr of unsupplemented greenhouse daylight and the long photoperiod treatment of greenhouse daylight at the natural photoperiod of Santa Cruz, California (37° N) plus a 3-hr night interruption (0.25 mW/cm²). Growth was measured by total stem length and leaf resin sesquiterpene composition was quantitatively analyzed by GLC. Photoperiod had no significant effect on leaf resin chemistry but the longer photoperiod markedly promoted vegetative growth. Large population differences in overall vegetative growth and quantitative leaf resin composition were also evident. Growth patterns indicated that the low intensity night break had little or no effect on growth.     

Compositional variation of leaf pocket sesquiterpenes in Trachylobium verrucosum

Greenhouse-grown plants originating from Kenyan and Madagascan populations of Trachylobium verrucosum are qualitatively identical in leaf pocket resin sesquiterpene composition, but differ quantitatively.     

Implications of variation in resin composition among organs, tissues and populations in the tropical legume Hymenaea

Variation in leaf blade, petiole and primary stem resins, composed of sesquiterpene hydrocarbons, is analysed in two contrasting species of the tropical legume Hymenaea. Five populations of the New World H. courbaril, spanning a wide range of ecosystems, are compared with a population of the disjunct African H. verrucosa. Resins in petiole and primary stem tissue are similar, but differ significantly in total composition from leaf blade tissues. The major components, caryophyllene, - and β-selinene and β-copaene vary most significantly among the tissues, but all compounds vary at highly significant levels among populations. The variation patterns in resin composition among the leaf blade and petiole/primary stem tissues are put into a larger context of comparison with the primarily diterpenoid patterns in secondary stem and pod tissues. Although the comparatively minor quantitative differences in the sesquiterpene systems could be attributed solely to developmental and physiological differences among the tissues and populations, the total weight of accumulating evidence regarding quantitative variation and demonstrated toxic and deterrent properties of sesquiterpene resins to insect herbivores leads us to hypothesize a possible role of differential predator pressures.     

Compensatory response of a legume root-nodule system to nodule herbivory by Sitona hispidulus

A laboratory study was conducted to examine the hypothesis that herbivory of nitrogen-fixing root nodules on legumes causes an exact compensatory response in nodule growth. Plants of Medicago sativa (L.) were grown hydroponically in clear plastic growth pouches so that the number and biomass of root nodules could be estimated nondestructively before, and 10 and 18 days after, partial denodulation. For treatments, plants were subjected to 23% denodulation by first-instar larvae of Sitona hispidulus (F.) (a common herbivore of Medicago and Trifolium) or 50% nodule pruning; additional plants were left untreated. Results indicated that nodule herbivory and nodule pruning caused an overcompensatory response in number of nodules. This was also true for number of nodule units (an indirect measure of nodule biomass) per plant at 10 days after denodulation but had changed to an exact compensatory response by day 18. An inverse relationship between change in number of nodule units and initial number of nodules indicated that compensatory nodulation was regulated by a feedback mechanism. Shoot and root biomasses were not affected by denodulation in this study.     

Effect of moisture stress on composition and yield in leaf resin of Hymenaea courbaril

Previous controlled environment studies of the effect of photoperiod, light intensity and temperature have shown little phenotypic plasticity in leaf resin composition of Hymenaea courbaril which ranges throughout New World lowland tropical ecosystems. The present control chamber study also showed negligible variation in resin composition as a result of moisture status. Although some change in composition occurred under dry treatment conditions, leaf development was retarded and the variation is consistent with the progressive change in composition with leaf development from very young to fully expanded leaves. Yield (mg resin/g leaf tissue), not measured in previous studies, also showed little variation between wet and dry treatments. It is suggested that these indications of low plasticity in both composition and yield in Hymenaea leaf resins may be significant in herbivore interactions.     

Variation of Satureja douglasii monoterpenoids in relation to light intensity and herbivory

Genotypic variation of monoterpenoid yield and composition in Satureja douglasii was shown by growth of clonal transplants under uniform conditions. Differentiation of monoterpenoid yield was correlated with light intensity and degree of herbivory along transects. High-yielding genotypes occurred under low light, high herbivory conditions, whereas low-yielding genotypes occurred in high light, low herbivory conditions. Differentiation of monoterpenoid composition was more weakly correlated with herbivory and light intensity than was yield. There was also some evidence for seasonal variations of yield.     

Intraindividual variations of volatile terpene contents in Pinus caribaea needles and its possible relationship to Atta laevigata herbivory

Volatile terpene content variations in Pinus caribaea needles are examined in relation to season, dry hour, and canopy level. According to the results, the concentration of ß-pinene was lower and that of sabinene and caryophyllene higher in the dry season than in the rainy season. ß-Pinene, camphene, and ß-phellandrene were more abundant in needles located at the lower canopy level, and limonene, -ocimene, and the mixture of myrcene+-phellandrene were more abundant at the upper canopy level. Camphene, sabinene, myrcene+-phellandrene, and ß-cadinene+γ-cadinene were more abundant in the afternoon, with lower concentrations at night. These results indicate that intraindividual variations in the contents of volatile terpenes in Pinus caribaea needles are significant even in regard to interindividual differences. The foraging pattern of the leafcutting ant Atta laevigata, as observed in a Caribbean pine plantation, could be, in part, related to these intraindividual variations.     

Concentration of glucosinolates in relation to habitat and insect herbivory for the native crucifer Cardamine cordifolia

Understanding plant-insect interactions requires further data on herbivory in relation to the variation in concentration of characteristic secondary compounds. We report here analyses of the glucosinolate contents for a native perennial, montane crucifer Cardamine cordifolia in relation to: (a) plant characteristics; (b) insect herbivory; and (c) habitat. The only pattern of variation of glucosinolate content with leaf characteristics found was an inverse correlaton between leaf weight and total isothiocyanate-yielding glucosinolates (IYG) in shaded plants. There was a highly significant, negative relationship between total IYG and leaf damage by insects, particularly in typical shaded habitats. Higher insect-caused damage on denser, smaller leaves of plants from the driest soils was observed. Additionally, plants occurring in sun-exposed habitats from the beginning of the growing season, both naturally and experimentally, had similar (or lower) concentrations of total IYG, and were significantly more damaged by insects, than those in the more usual shaded habitats. The experimental removal of shade cover in mid-season resulted in significantly elevated quantities of total IYG in the first year, with a relaxation of that stress-induced response in the second year. We suggest that the insect herbivore guild on Cardamine cordifolia responds to concentration and composition of glucosinolates and exerts its greatest pressure on plants with lower concentrations. Differential herbivory, consumption mediated in part by glucosinolate concentration, appears to contribute to microhabitat occurrence of C. cordifolia.     

Leaf miners on Ochna ciliata (Ochnaceae) growing on Aldabra Atoll: patterns of herbivory in relation to goat browsing and exposure to the sun

Abstract.

• 1 The patterns of herbivory by leaf miners on the shrub Ochna ciliata growing on Aldabra Atoll were studied in relation to browsing by feral goats and exposure to the tropical sun versus shading.
• 2 Damage due to both tunnelling (Diptera) and ‘blotch-making’ (Lepidoptera) leaf miners was statistically greater on trees that had been browsed and on those that received more extensive exposure to the sun.
• 3 Effects of exposure and browsing were additive, as evidenced by the lack of statistical interaction between these factors.
• 4 There was a significant negative correlation between the numbers of tunnelling and blotch-making miners in trees that had been browsed, but not in unbrowsed trees.
• 5 Three geographical areas were sampled to test whether the effects of browsing on leaf mining were invariant or influenced by as yet unknown environmental factors. A statistically significant interaction between browsing and geographical region indicated that, while browsed trees had significantly more mines whatever the habitat, the extent of this effect differed across the habitats.

     

Tolerance of Gentianella campestris in relation to damage intensity: an interplay between apical dominance and herbivory

Meristem allocation models suggest that the patterns of compensatory regrowth responses following grazing vary, depending on (i) the number of latent meristems that escape from being damaged, and (ii) the activation sensitivity of the meristems in relation to the degree of damage. We examined the shape of compensatory responses in two late-flowering populations (59°20′N and 65°45′N) of the field gentian. Plants of equal initial sizes were randomly assigned to four treatment groups with 0, 10, 50 and 75% removal of the main stalk. The plants were clipped before flowering, and their performance was studied at the end of the growing season. The northern population showed a linear decrease in shoot biomass and fecundity with increasing biomass removal, while the response in the southern population was quadratic with maximum performance at the damage level of 50% clipping. This nonlinear shape depended upon the activation sensitivity of dormant meristems in relation to their position along the main stem. The highest plant performance was achieved by inflicting intermediate damage which induced regrowth from basally located meristems. In contrast, the topmost branches took over the dominance role of the main stem after minor apical damage (10% clipping). Consequently, the breakage of apical dominance is a necessary precondition of vigorous regrowth in this species. However, compensation in the field gentian is unlikely to be a mere incidental by-product of apical dominance. The ability to regrow from basally located meristems that escape from being damaged by grazing may well be a sign of adaptation to moderate levels of shoot damage. This revised version was published online in July 2006 with corrections to the Cover Date.     

Essential leaf oil variability in green,variegated and albino foliage of Myrtus communis

Green, variegated and albino leaves of Myrtus communis yield mono- and sesqui-terpenes which show considerable variation in their ratios when compa     

Latitudinal patterns in plant defense: evolution of cardenolides, their toxicity and induction following herbivory

Attempts over the past 50 years to explain variation in the abundance, distribution and diversity of plant secondary compounds gave rise to theories of plant defense. Remarkably, few phylogenetically robust tests of these long-standing theories have been conducted. Using >50 species of milkweed (Asclepias spp.), we show that variation among plant species in the induction of toxic cardenolides is explained by latitude, with higher inducibility evolving more frequently at lower latitudes. We also found that: (1) the production of cardenolides showed positive-correlated evolution with the diversity of cardenolides, (2) greater cardenolide investment by a species is accompanied by an increase in an estimate of toxicity (measured as chemical polarity) and (3) instead of trading off, constitutive and induced cardenolides were positively correlated. Analyses of root and shoot cardenolides showed concordant patterns. Thus, milkweed species from lower latitudes are better defended with higher inducibility, greater diversity and added toxicity of cardenolides.     

Leaf trichome responses to herbivory in willows: induction, relaxation and costs

Direct measurement of the carbon (C) 'cost' of mycorrhizas is problematic. Although estimates have been made for arbuscular and ectomycorrhizal symbioses, these are based on incomplete budgets or indirect measurements. Furthermore, the conventional model of unidirectional plant-to-fungus C flux is too simplistic. Net fungus-to-plant C transfer supports seedling establishment in c. 10% of plant species, including most orchids, and bidirectional C flows occur in ectomycorrhiza utilizing soil amino acids. Here, the C cost of mycorrhizas to the green orchid Goodyera repens was determined by measurement of simultaneous bidirectional fluxes of 14C labelled sources using a monoxenic system with the fungus Ceratobasidium cornigerum. Transfer of C from fungus to plant ('up-flow') occurs in the photosynthesizing orchid G. repens (max. 0.06 microg) whereas over five times more current assimilate (min. 0.355 microg) is simultaneously allocated in the reverse direction to the mycorrhizal fungus ('down-flow') after 8 d. Carbon is transferred rapidly, being detected in plant-fungal respiration within 31 h of labelling. This study provides the most complete C budget for an orchid-mycorrhizal symbiosis, and clearly shows net plant-to-fungus C flux. The rapidity of bidirectional C flux is indicative of dynamic transfer at an interfacial apoplast as opposed to reliance on digestion of fungal pelotons.     

Evolutionary ecology of resistance to herbivory: an investigation of potential genetic constraints in the multiple-herbivore community of Solanum carolinense

As part of a study of the ecological and evolutionary dynamics of herbivore resistance in Solanum carolinense (horsenettle), potential genetic constraints to the evolution of resistance to 11 of its most common herbivores were investigated. Leaf, flower, fruit, and stem herbivory were measured in a field experiment involving 24 ramets of each of 40 horsenettle genets. The experimental plant population contained significant genetic variation for resistance to all 11 species of herbivore. For only one species was there an indication of a genotype-by-environment interaction in the expression of resistance that might constrain its evolution. Genetic correlations in resistance to different species were common but not universal, with seven negative and 12 positive correlations out of the 55 pairwise species comparisons. Correlations were independent of plant part fed upon. The evolution of the resistance of horsenettle to most of its diverse community of herbivores does not appear to be prevented by a lack of genetic variation or by genotype-by-environment interactions in resistance. Negative genetic correlations in resistance to different herbivores may play a small role in slowing the evolution of resistance, but positive correlations may play at least as large a role in facilitating its evolution.