Most ants of the genus Pseudomyrmex are arboreal and are part of a pantropical group of arboreal, twig-dwelling ants confined to tropical forests, woodlands, and savannas.
Among the estimated 300 species of Pseudomyrmecine ants (subfamily which includes the Pseudormyrmex genus), 20% have an obligate symbiotic relationship with Myrmecophite plants.
Evolutionarily speaking, the relationship between the ants and domatia bearing plants is believed to have evolved at least 12 times within the subfamily. Some examples of the genera of these ant-plants found in the neotropics are Cordia, Mycia, Tachigali and Triplaris. Five species of Pseudomyrmex are obligate associates of trees in the genus Triplaris (Ward 2002).
In most instances, the plant provides a hollow or excavated cavity (domatium), in which the ants keep brood and scale insects. Scale insects are small insects from the order Hemiptera classified in the subfamily Coccoidea. In exchange, the ants protect the plant from herbivores and sometimes, from other competing plants that may grow on or around the tree (Ward and Downie 2005).
This type of relationship is not unique. As a matter of fact, there are hundreds of plants in more than 40 families that possess specialized structures to house ants and many of these plants also supply nectar and food bodies to the ants. In exchange for this shelter and nourishment, the ants are responsible for clearing the vegetation surrounding the plant, and protecting it from herbivores. As there is a symbiotic relationship between ant and plant, both benefit from the well-being of the other. Thus, as the plant’s growth is strengthened, the ants benefit from the increased health and vigor of the host plant (Davidson et al. 1988).
It has been observed that when Pseudomyrmex colonies are removed from their host plants, the plants growth rate and fitness decline as there is an obvious increase in herbivory and competition with shading vines (Davidson et al. 1988). The ants vary in aggressiveness and in defense tactics. Some very aggressive species of this ant have been known to sprint onto humans in the vicinity of the plant, warned by only the body odor of the person, instantly beginning to sting and grasp onto them, to the point that the ants can only be removed manually. Pseudomyrmex ants are among the most widely distributed of the Triplaris-inhabiting ants, ranging from southern Colombia through the Amazon basin to Bolivia and the southwestern Brazil
It’s believed that the relationship between the Pseudomyrmex ants and the Triplaris plant has existed for at least several million years, and possibly much more (Ward 2002). Workers readily attack intruders and they clear vegetation from the base of the host tree. Triplaris Americana is one of the species of Triplaris that is known to have a relationship with these ants.
Interestingly enough, the species of Pseudomyrmex triplarinus has a venom that has been analzed and it seems as though it has some qualities which can be used in the treatment of rheumatoid arthritis (Ward 2002). Its venom has anti-inflammatory properties (Pan and Hink 2000) and analgesic agents useful in treating autoimmune diseases, especially rheumatoid arthritis (Sukhwani). The venom has been extracted from the venom sac of the ant and the analysis shows that it has high contents of glycoprotein, heparin, chondroitin sulphate, polysaccharides and other hydrocarbons. It has high activity when it is highly purified, with very few adverse effects, allowing for long-lasting results.
Pseudomyrmecine ants are omnivores, feeding on things such as honey, crickets and pollen. They are able to communicate the presence of food and are always seen foraging in large numbers. They are also highly territorial and their markings, which are colony specific, can last 30-60 minutes.
The Triplaris trees to which these ants can be found to be associated, have a hollow heart. The ants enter the trunk by perforating a 2mm-in-diameter entrance in many places along the trunk and twigs, to make their way to the central opening (Jaffe et al. 1986). The wastes of the colony do not remain within the trees corridors; rather they are thrown out, down the tree.
The Triplaris tree has quite an interesting history with the natives in the area. It’s known as the ‘justice tree’ in certain tribes, such as the Machiguenga and the Ese Eja. The reason they give this plant such a name, is that this tree was used to punish people from the communities, who didn’t respect the rules. The rule-breakers were tied to the tree using, for hours, using a very strong liana, which could not be broken, until they begged for forgiveness for their mistakes.
It’s also said that, many years ago, when the first pioneers came to the Madre de Dios area, from different cities around Peru (Pucallpa, Iquitos, Tarapoto), the hunters, hoping to encounter large prey such as tapirs, wild boars and monkeys, instead encountered many cadavers tied to these trees. Around the cadavers of the indigenous people, the hunters found arrows and tribal gowns.
One of the interpreters at the lodge performed a small study on these tangarana ants to see how far from the tree the ants would clear the vegetation. Moises, the guide, planted beans and let them sprout, measuring the distance from the tree and the saplings. His studies lead him to conclude that these ants clear the vegetation around the tree, up to a distance of 120cm.
Another well known relationship found with Pseudomyrmex ants is between them and Acacia plants. In this relationship, the ants help the plant by clearing the vegetation within a radius of 40cm of the acacia trunks (Davidson et al.). Unlike the Pseudomyrmex triplarinus species, the ants related to the acacia trees live in ant gardens, not cavities in the plant. This is considered the most complex and sophisticated of all symbioses between ants and flowering plants. “Ant gardens are large masses of soil, detritus and chewed vegetable fibers that are assemble into round masses in the branches of the trees and bushes. They range in size from gold balls to soccer balls, within which are grown a variety of herbaceous plants (Davidson et al.).”
This very interesting relationship occurs when the ants collect the materials they use to build their nests. While gathering the soil and plant matter, they also gather seeds of symbiotic plants, also placing them in the nest. These seeds then grow into plants, which are nourished by the materials in the nest, and the roots become part of the nests’ framework. The ants then feed on the food bodies, fruit, pulp and nectar provided by the plants.
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