Leaf volatile compounds and the distribution of ant patrollingin an ant-plant protection mutualism: Preliminary results onLeonardoxa (Fabaceae: Caesalpinioideae) andPetalomyrmex(Formicidae: Formicinae) (original) (raw)
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Chemoecology, 2006
We examined the role of plant phenology in the evolution of anti-herbivore defence in symbiotic ant-plant protection mutualisms. Phenology of the host-plant affects traits of its herbivores, including size, growth rate, development time, and gregariousness. Traits of herbivores in turn determine what traits ants must have to protect their host. Diversity in plant phenological traits could thus help explain the great ecological diversity of coevolved ant-plant mutualisms. We explored the postulated causal chain linking phenology of the plant, herbivore adaptations to phenology, and ant adaptations for protection, by comparing two myrmecophytes presenting strong contrasts in phenology. In Leonardoxa africana, a slow-growing understory tree, growth at each twig terminal is intermittent, the rapid flushing of a single leaf-bearing internode being followed by a pause of several months. In contrast, axes of Barteria nigritana, a tree of open areas, grow continuously. Analysis of the phenology (kinetics of expansion) and chemistry of leaf development (contents of chlorophylls, lignin, and nitrogen during leaf growth) showed that these two species exhibit strongly contrasting strategies. Leonardoxa exhibited a delayed greening strategy, with rapid expansion of leaves during a short period, followed by synthesis of chlorophylls and lignins only after final leaf size has been reached. In contrast, leaves of Barteria expanded more slowly, with chlorophylls and lignin gradually synthesised throughout development. Differences in the phenology of leaf development are reflected in differences in the duration of larval development, and thereby in size, of the principal lepidopteran herbivores observed on these two plants. This difference may in turn have led to different requirements for effective defence by ants. The strategy of phenological defence may thus affect the evolution of biotic defence.
Biotropica, 2006
We compared the effects of ant presence at extrafloral nectaries of Lafoensia pacari St. Hil. on herbivore damage and silicon accumulation. Plants that were accessible to ants experienced lower herbivory levels over the first 3 mo of the experiment. After 3 mo, most leaves were fully expanded with inactive extrafloral nectaries; by 6 mo there was no effect of ant access on herbivore damage. Along with experiencing higher herbivory, plants in the ant-exclusion treatment had significantly higher silicon levels in their leaves, suggesting that silicon serves as an induced defense in this ant-plant-herbivore interaction.
Interspecific variation in the defensive responses of ant mutualists to plant volatiles
2008
Ants that defend plants from herbivores in exchange for rewards such as food or shelter are a defining characteristic of tropical forests, with over 100 plant genera and 40 ant genera participating in these mutualisms (Benson, 1985; Davidson & McKey, 1993). These ants are often obligately associated with their host plants, and establish colonies solely in swollen thorns, leaf pouches, hollow stems, and other specialized structures known as domatia.
Oecologia, 1983
Foragers of the leafcutting ant, Atta cephalotes L. (Formicidae, Attini) seldom or never attack many of the plant species available to them in nature. In the semideciduous forests of lowland Guanacaste Province, Costa Rica, one of the tree species seldom cut is Hymenaea courbaril L. (Leguminosae, Caesalpinioideae). We tested the hypothesis that this species is avoided by the ants because of the presence of ant-repellent secondary compounds in the leaves. A bioassay to test repellency of leaf extracts was developed to guide the chemical isolation of ant repellents, using a laboratory colony of Atta cephalotes. The presence of one or more extractable ant repellents was quickly demonstrated. Subsequent chemical isolation and identification revealed that there was essentially only one terpenoid responsible for the repellency: caryophyllene epoxide. Tests with a concentration series of the pure compound demonstrated that the natural concentration of this terpenoid in Hymenaea could fully account for the observed repellency of intact leaves. Field bioassays of the terpenoid in Costa Rica confirmed this result; leaves of a preferred species, Spondias purpurea L. (Anacardiaceae), became as repellent as Hymenaea leaves when treated with caryophyllene epoxide at natural Hymenaea leaf concentrations. Repellency of the epoxide was 20 times greater than that of caryophyllene, its sesquiterpene hydrocarbon precursor, which is also found in Hymenaea leaves. Attine ants cut leaves to serve as substrate for culturing a specific fungus for food, principally for their larvae. A reasonable hypothesis is that these ants selectively avoid plant species whose leaves contain compounds which are toxic to their fungus. We tested caryophyllene epoxide for antifungal activity and found that it is an extremely potent compound, not only against the attine fungus, but other fungi as well. We speculate that many of the other plant species avoided by these ants in nature may be similarly protected from ant attack by antifungal compounds in their leaves. We further suggest that plant defense against leafcutting ants may be largely an incidental byproduct of selection for fungal resistance in plants.
Biological Defense in Passiflora Incarnata: Evidence for a Chemical Defense Against Ant Defenders
Passiflora incarnata plants produce extrafloral nectar that is attractive to ants which, in turn, can act as predators to herbivorous insects. There is a potential cost to protection via ants, as the reproductive success of plants can be reduced if ants remove floral nectar. We asked whether floral nectar and/or floral tissues contain a chemical that would deter ant visitation. In a Petri dish, we allowed individuals from each of two ant species (Camponotus floridana and Pseudomyrmex gracilis) to choose among three nectar solutions (extrafloral nectar (EN), floral nectar (FN), and floral nectar with extract from floral tissues (FN+FE)). In addition, ants of each species were placed into individual Petri dishes in which we spread macerated floral tissue over one half of the top and bottom and distilled water over the other half. When given a choice of nectar types, neither ant species demonstrated a preference for EN over FN, but both tended to avoid FN+FE. In addition, ants spent an average of less than one out of 10 minutes walking within the side of a Petri dish containing floral extract. Our results demonstrate that P. incarnata flowers produce a chemical in tissues, but not in floral nectar, that can deter ant visitors.
Chemical Released from Host Acacia by Feeding Herbivores is Detected by Symbiotic Acacia-ants.
The plant-ants, Pseudomyrmex spinicola and P. flavicornis protect their host tree, Acacia collinsii, from herbivores. Tissue disruption of leaves, like that caused by herbivory, attracts the ants and causes them to display intense alarm behavior. Solid phase microextraction (SPME) showed trans-2-hexenal was the major volatile chemical produced from crushed acacia leaves. Bioassays of this chemical showed that it attracted these ants and initiated an alarm response.
Chemical defenses in the tree Ziziphus mistol against the leaf-cutting ant Acromyrmex striatus
2002
Ziziphus mistol Griseb. (Rhamnaceae) trees are avoided by the leaf-cutting ant Acromyrmex striatus Roger (Formicidae, Attini) in a semi-arid Chaco forest of Santiago del Estero Province, Argentina. In order to find out the chemical fraction responsible of ant rejection, we analyzed putative chemical defenses (tannins, phenolics and saponins) in young and mature leaves of Ziziphus mistol and carried out field bioassays to test both polar and non-polar leaf extracts for ant-repellence. We included into our bioassays two flavonoid compounds, namely quercetin and its glycoside rutin, which are common in Ziziphus mistol leaves, and commercial quebracho tannin. Condensed tannins and total phenols were significantly in higher concentra- tions in mature than in young leaves. We were unable to detect hydrolyzable tannins on both young and mature leaves. Saponins were only detected in young leaves. The non-polar extract was significantly repellent, whereas the polar extract was not significan...
Ant-Acacia interaction: Chemical or physical defense?
Entomological Research, 2011
Two different ant-Acacia ecosystems at two different sites were investigated for comparing their lifestyles. One ecosystem is at St. Katherine's Protectorate and the other at Ismailia Province, Egypt. The defense mechanisms that each Acacia tree use against browsers were investigated. Seasonal and daily abundances of ants and other herbivores on two Acacia trees were studied. The study indicated different defense mechanisms used by these two Acacia species: Acacia use both physical and chemical defense mechanisms. The efficiency of both mechanisms in defending Acacia against herbivores and why Acacia trees preferred one mechanism to the other are discussed._ 330 135..141
Plant-based compounds with potential as push-pull stimuli to manage behavior of leaf-cutting ants
Entomologia Experimentalis et Applicata, 2017
Leaf-cutting ants are a serious pest of young forestry plantations. Currently, the main control method is the use of broad-spectrum insecticides, which have a negative effect on non-target organisms and the environment. In this work, plant-based compounds were evaluated in laboratory assays with Acromyrmex ambiguus Emery (Hymenoptera: Formicidae) for their potential use as repellent and attractant stimuli to be used in a push-pull strategy. Farnesol, a sesquiterpene present in many essential oils, was tested as a repellent at doses of 10, 50, and 100 mg. Its distance of action was studied by comparing the repellent effect of farnesol in a situation in which ants had to touch the farnesol in order to reach the food source in comparison to when ants could reach the food source without getting into direct contact with it. Different parts of the orange fruit (pulp and peel) were evaluated and compared as attractants, given that citrus-based baits are among the most popular attractants used. Results from laboratory bioassays indicated that farnesol is repellent at doses of 50 mg and acts upon contact or at a very short distance. Furthermore, orange pulp was more attractive than the peel, and volatile compounds were highly responsible for the attraction. When both stimuli were tested simultaneously in a laboratory experiment, repellency of farnesol was enhanced in the presence of orange pulp odor. When tested in a field push-pull experiment, the results also showed a good repellent effect of farnesol as well as an attractant effect of the orange pulp. These results encourage long-term studies with these substances in a field setting and suggest that repellents can be enhanced by the use of attractants to manage leaf-cutting ants behavior.
We compared the effects of ant presence at extrafloral nectaries of Lafoensia pacari St. Hil. on herbivore damage and silicon accumulation. Plants that were accessible to ants experienced lower herbivory levels over the first 3 mo of the experiment. After 3 mo, most leaves were fully expanded with inactive extrafloral nectaries; by 6 mo there was no effect of ant access on herbivore damage. Along with experiencing higher herbivory, plants in the ant-exclusion treatment had significantly higher silicon levels in their leaves, suggesting that silicon serves as an induced defense in this ant-plant-herbivore interaction.