Harnessing ant defence at fruits reduces bruchid seed predation in a symbiotic ant-plant mutualism.

In horizontally transmitted mutualisms, mutualists disperse separately and reassemble in each generation with partners genetically unrelated to those in the previous generation. Because of this, there should be no selection on either partner to enhance the other's reproductive output directly. In symbiotic ant-plant mutualisms, myrmecophytic plants host defensive ant colonies, and ants defend the plants from herbivores. Plants and ants disperse separately, and, although ant defence can indirectly increase plant reproduction by reducing folivory, it is unclear whether ants can also directly increase plant reproduction by defending seeds. The neotropical tree Cordia alliodora hosts colonies of Azteca pittieri ants. The trees produce domatia where ants nest at stem nodes and also at the node between the peduncle and the rachides of the infloresence. Unlike the stem domatia, these reproductive domatia senesce after the tree fruits each year. In this study, I show that the tree's resident ant colony moves into these ephemeral reproductive domatia, where they tend honeydew-producing scale insects and patrol the nearby developing fruits. The presence of ants significantly reduced pre-dispersal seed predation by Amblycerus bruchid beetles, thereby directly increasing plant reproductive output.

Plant profile, phytochemistry and pharmacology of Cordia dichotoma (Indian cherry): a review.

More than half of the world's population relies on the traditional medicine and major role of the traditional medicine including the use of plant extract and their active constituents. Among them, Cordia dichotoma Forst., a small to moderate size plant of family Boragenaceae, commonly called bhokar, lasura, gonda, Indian cherry and shlesmataka. Plant parts such as leaves, fruit, bark and seed have been reported for possessing antidiabetic, antiulcer, anti-inflammatory, immune-modulator and analgesic activity. Screening of fruit, leaves and seed shows the presence of pyrrolizidine alkaloids, coumarins, flavonoids, saponins, terpenes and sterols. Present review focuses on details of geographical distribution, physicochemical parameters, phytoconstituents and pharmacological properties of Cordia dichotoma reported so far.

Plant defense, herbivory, and the growth of Cordia alliodora trees and their symbiotic Azteca ant colonies.

The effects of herbivory on plant fitness are integrated over a plant's lifetime, mediated by ontogenetic changes in plant defense, tolerance, and herbivore pressure. In symbiotic ant-plant mutualisms, plants provide nesting space and food for ants, and ants defend plants against herbivores. The benefit to the plant of sustaining the growth of symbiotic ant colonies depends on whether defense by the growing ant colony outpaces the plant's growth in defendable area and associated herbivore pressure. These relationships were investigated in the symbiotic mutualism between Cordia alliodora trees and Azteca pittieri ants in a Mexican tropical dry forest. As ant colonies grew, worker production remained constant relative to ant-colony size. As trees grew, leaf production increased relative to tree size. Moreover, larger trees hosted lower densities of ants, suggesting that ant-colony growth did not keep pace with tree growth. On leaves with ants experimentally excluded, herbivory per unit leaf area increased exponentially with tree size, indicating that larger trees experienced higher herbivore pressure per leaf area than smaller trees. Even with ant defense, herbivory increased with tree size. Therefore, although larger trees had larger ant colonies, ant density was lower in larger trees, and the ant colonies did not provide sufficient defense to compensate for the higher herbivore pressure in larger trees. These results suggest that in this system the tree can decrease herbivory by promoting ant-colony growth, i.e., sustaining space and food investment in ants, as long as the tree continues to grow.

The evolution of intermediate castration virulence and ant coexistence in a spatially structured environment.

Theory suggests that spatial structuring should select for intermediate levels of virulence in parasites, but empirical tests are rare and have never been conducted with castration (sterilizing) parasites. To test this theory in a natural landscape, we construct a spatially explicit model of the symbiosis between the ant-plant Cordia nodosa and its two, protecting ant symbionts, Allomerus and Azteca. Allomerus is also a castration parasite, preventing fruiting to increase colony fecundity. Limiting the dispersal of Allomerus and host plant selects for intermediate castration virulence. Increasing the frequency of the mutualist, Azteca, selects for higher castration virulence in Allomerus, because seeds from Azteca-inhabited plants are a public good that Allomerus exploits. These results are consistent with field observations and, to our knowledge, provide the first empirical evidence supporting the hypothesis that spatial structure can reduce castration virulence and the first such evidence in a natural landscape for either mortality or castration virulence.

Conflict over reproduction in an ant-plant symbiosis: why Allomerus octoarticulatus ants sterilize Cordia nodosa trees.

The evolutionary stability of mutualism is thought to depend on how well the fitness interests of partners are aligned. Because most ant-myrmecophyte mutualisms are persistent and horizontally transmitted, partners share an interest in growth but not in reproduction. Resources invested in reproduction are unavailable for growth, giving rise to a conflict of interest between partners. I investigated whether this explains why Allomerus octoarticulatus ants sterilize Cordia nodosa trees. Allomerus octoarticulatus nests in the hollow stem domatia of C. nodosa. Workers protect C. nodosa leaves against herbivores but destroy inflorescences. Using C. nodosa trees with Azteca ants, which do not sterilize their hosts, I cut inflorescences off trees to simulate sterilization by A. octoarticulatus. Sterilized C. nodosa grew faster than control trees, providing evidence for a trade-off between growth and reproduction. Allomerus octoarticulatus manipulates this trade-off to its advantage; sterilized trees produce more domatia and can house larger, more fecund colonies.

The reproductive phenology of an Amazonian ant species reflects the seasonal availability of its nest sites.

In saturated tropical ant assemblages, reproductive success depends on queens locating and competing for scarce nest sites. Little is known about how this process shapes the life histories of tropical ants. Here I investigate the relationship between nest site availability and an important life history trait, reproductive phenology, in the common Amazonian ant species Allomerus octoarticulatus. A. octoarticulatus is a plant-ant that nests in the hollow, swollen stem domatia on Cordia nodosa. I provide evidence that nest sites are limiting for A. octoarticulatus. Most queens produced by A. octoarticulatus colonies died before locating suitable host plants, and most queens that located hosts died before founding colonies, probably from intraspecific competition among queens for control of host plants. I further show that the reproductive phenology of A. octoarticulatus closely matches the seasonal availability of its nest sites, domatia-bearing C. nodosa saplings. Both the production and flight of A. octoarticulatus reproductives, and the number of C. nodosa saplings available for colonization by ants, peaked from March to May. There was correlative evidence that A. octoarticulatus colonies use temperature as a cue to synchronize their reproduction to the availability of C. nodosa saplings: both the production of reproductives by ant colonies and the number of C. nodosa saplings available for colonization were correlated with temperature, and not with rainfall. All of these results suggest that nest site limitation constrains the reproductive phenology of A. octoarticulatus.

Selection for protection in an ant-plant mutualism: host sanctions, host modularity, and the principal-agent game.

Retaliation against cheaters can prevent the breakdown of cooperation. Here we ask whether the ant-plant Cordia nodosa is able to apply retaliatory sanctions against its ant symbiont Allomerus octoarticulatus, which patrols new shoots to prevent herbivory. We test the hypothesis that the modular design of C. nodosa physiologically ties the growth of housing (stem swellings known as domatia) to the successful development of the attached leaves. We experimentally simulated herbivory by cutting leaves from patrolled shoots and found that the domatia on such 'cheated' shoots suffered higher mortality and lower growth than did controls, evidence for a host sanction. On the other hand, patrolling is costly to the ant, and experiment shows that non-patrollers run a low risk of being sanctioned because most leaves (and the attached domatia) escape heavy herbivory even when patrollers are absent. This suggests that cheaters might enjoy a higher fitness than do mutualists, despite sanctions, but we find that patrolling provides a net fecundity benefit when the colony and plant exceed a minimum size, which requires sustained ant investment in patrolling. These results map directly onto the principal-agent (P-A) game from economics, which we suggest can be used as a framework for studying stability in mutualisms, where high sampling costs and cheating do not allow market effects to select for mutual benefits.

Ant species confer different partner benefits on two neotropical myrmecophytes.

The dynamics of mutualistic interactions involving more than a single pair of species depend on the relative costs and benefits of interaction among alternative partners. The neotropical myrmecophytes Cordia nodosa and Duroia hirsuta associate with several species of obligately symbiotic ants. I compared the ant partners of Cordia and Duroia with respect to two benefits known to be important in ant-myrmecophyte interactions: protection against herbivores provided by ants, and protection against encroaching vegetation provided by ants. Azteca spp., Myrmelachista schumanni, and Allomerus octoarticulatus demerarae ants all provide the leaves of Cordia and Duroia some protection against herbivores. However, Azteca and Allomerus provide more protection than does Myrmelachista to the leaves of their host plants. Although Allomerus protects the leaves of its hosts, plants occupied by Allomerus suffer more attacks by herbivores to their stems than do plants occupied by other ants. Relative to Azteca or Allomerus, Myrmelachista ants provide better protection against encroaching vegetation, increasing canopy openness over their host plants. These differences in benefits among the ant partners of Cordia and Duroia are reflected in the effect of each ant species on host plant size, growth rate, and reproduction. The results of this study show how mutualistic ant partners can differ with respect to both the magnitude and type of benefits they provide to the same species of myrmecophytic host.

Friend or foe? A behavioral and stable isotopic investigation of an ant-plant symbiosis.

In ant-plant symbioses, the behavior of ant inhabitants affects the nature of the interaction, ranging from mutualism to parasitism. Mutualistic species confer a benefit to the plant, while parasites reap the benefits of the interaction without reciprocating, potentially resulting in a negative impact on the host plant. Using the ant-plant symbiosis between Cordia alliodora and its ant inhabitants as a model system, I examine the costs and benefits of habitation by the four most common ant inhabitants at La Selva Biological Station, Costa Rica. Costs are measured by counting coccoids associated with each ant species. Benefits include patrolling behavior, effectiveness at locating resources, and recruitment response. I also compare the diets of the four ant species using stable isotope analysis of nitrogen (N) and carbon (C). Ants varied in their rates of association with coccoids, performance of beneficial behaviors, and diet. These differences in cost, benefit, and diet among the ant species suggest differences in the nature of the symbiotic relationship between C. alliodora and its ants. Two of the ant species behave in a mutualistic manner, while the other two ant species appear to be parasites of the mutualism. I determined that the mutualistic ants feed at a higher trophic level than the parasitic ants. Behavioral and dietary evidence indicate the protective role of the mutualists, and suggest that the parasitic ants do not protect the plant by consuming herbivores.