Wednesday, April 4, 2012

Myrmelachista schumanni - The Ant Army of Devil Gardens

The ant species Myrmelachista schumanni is an inhabitant of the tree Duroia hirsutaD. hirsuta trees provide shelter and nutrients for the ants and in return M. schumanni protects the trees from predators and competitors. This mutualistic relationship is commonly observed in the Amazon rainforest where the association creates “devil gardens”. Devil gardens are clearings in the rainforest inhabited by only one or two, species of trees. They were given their name because the Andean people of Peru believed they were inhabited by evil spirits. However, it is now clear that M. schumanni is responsible for the clearings. 


The relationship is initiated when a queen Myrmelachista schumanni colonizes a single Duroia hirsuta tree. As the ant colony continues to grow, worker ants kill surrounding vegetation allowing more D. hirsuta trees to grow. The ants then spread to new D. hirsuta saplings and a devil garden begins to form [3]. M. schumanni workers continuously patrol the devil gardens. When they come across a plant other than D. hirsuta, hundreds of ants bite the leafs and stems of the intruder and proceed to inject formic acid into the puncture wounds. The plant begins to turn brown and the necrosis spreads, eventually killing the intruding plant [1]. In addition, M. schumanni also physically attacks insect herbivores of D. hirsuta promoting their survival and growth[3].
In return for their service, M. schumanni receives shelter and a food source from D. hirsuta trees. The trees have domatia which are hollow, swollen, structures in which the ants can nest. D. hirsuta provide nutrients directly via food bodies or extrafloral nectar, or indirectly via homopteran coccoids which are scale insects that are found on the trees that the ants can feed on [2].

Although M. schumanni is not the only ant species that forms a mutual relationship with D. histuta it is the only one responsible for forming devil gardens. It is the only ant species that eliminates encroaching vegetation thus M. schumanni can also form devil gardens of other myrmecophytes [2]. This is considered a mutualistic relationship because it is obligatory for the ants’ survival and both species benefit. Although, D. hirsuta can survive without M. schumanni, in the presence of M. schumanni their growth is significantly increased.

The presence of M. schumanni in D. hirsuta has two benefits for the trees: first, protection against insect herbivores and second, protection against encroaching vegetation. However, the development of devil gardens also has a potentially detrimental cost for D. hirsuta; with the development of monospecific stands of D. hirsuta herbivory increases as the number of D. hirsuta trees increases within a devil’s garden [3]. This negative feedback is thought to be the mechanism by which devil’s gardens are kept from over taking the Amazon. Another cost of housing M. schumanni is that the trees can be weakened by the chambers and passages created by the ants inside the tree [1]. This is not often observed but can occur. In light of these costs, from the point of view of D. hirsuta the relationship could be considered commensalism because it is not absolutely obligatory, however, it is much more beneficial for the D. hirsuta to associate with M. schumanni.

For M. schumanni the relationship is obligatory in order to have shelter and nutrients. The costs are minimal; only some energy is expended in order to protect D. hirsuta.  

1.       Edwards DP, Frederickson ME, Shepard GH, Yu DW. (2009) A Plant Needs Ants like a Dog Needs Fleas: Myrmelachista schumanni Ants Gall Many Tree Species to Create Housing. The American Naturalist . Vol. 174, No.5, pp. 734-740. 

2.       Frederickson, Megan E. (2004) Ant Species Confer Different Partner Benefits on Two Neotropical Myrmecophytes. Oecologia. Vol. 143, No. 3, pp. 387-395. 

3.       Frederickson ME, Gordon DM. (2007) The Devil to Pay: A Cost of Mutualism with Myrmelachista schumanni Ants in ‘Devil’s Gardens’ in Increased Herbivory on Duroia hirsuta Trees. Royal Society Publishing. Vol. 274, pp. 1117-1123. 

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