Allomerus Decemarticulatus - Plant Mutualism

Plant Mutualism

The relationship between A. decemarticulatus and H. physophora is very specialized. H. physophora is a small tree in the Amazonian rainforest that resides in the undergrowth. It is also an example of a myrmecophyte, because it contains ant-domatia, leaf pouches and hollow chambers where the ants nest permanently. These leaf pouches occur when the edge of a leaf adjacent to the petiole curls under. The result is two hollow spheres on both sides of the stem of the leaf. The ants live inside of these domatia. There is only one colony per tree, but that colony divides up into many different domatia. Also located in the leaf pouches are extrafloral nectaries, which provide the ants with nectar made by the plant, and also some food bodies that provide the ants with further nutrition as they mature to become foragers and insect predators. This is the first known instance of extrafloral nectaries being observed inside of ant-domatia.

So far this looks like simple parasitism by the ants, as if they simply take advantage of the plant for food and shelter. However, the plant also benefits greatly from this relationship. With the help of their traps and predation, the ants defend the plant from other insects and parasitic plants. Any insect that may kill or eat the plant is quickly captured and killed by the ants, which is also to their own benefit.

The specialized structures of the plant reveal a very interesting coevolution and symbiosis between these two species. A recent study performed by Céline Leroy et al. (2008) revealed many characteristics that the plant has adapted to support the ants. First, the domatia are located next to the stems that the ants use for hunting. Second, they contain extrafloral nectaries and food bodies to feed the ants if they do not have other sources of food. Third, there are less chloroplasts found inside of the domatia, which means that it has a lower photosynthetic capacity. Fourth, more stomata were found inside of the domatia, apparently there to capture the carbon dioxide from the ants’ respiration taking place inside. Finally, there was a greater deposit of cellulose found in the domatia, which would result in a thicker cell wall and a more rigid surface to support the weight of the ants. These findings show that the areas destined to become domatia are inherited and a result of coevolution; they were solely produced to support this specific species of ant.