Mutualism in nature has always been something that interests me, and in my eyes one of the more amazing examples would have to be the relationship between certain ants and plants. These relationships can be relatively simple, where the plant produces supplemental food, or more complex with the plant providing a home for the ants.
Plants which produce supplementary food can do so via small food nodules, or by the production of sugary secretions at extrafloral nectaries (basically, a nectary outside of a flower). These attract ants, which benefit from the easily harvested nutrient, and in turn this benefits the plant because the ants defend the food supply.
The next step up is plants which actually create an area for the ants to inhabit (domatia). These can range from simple hollow thorns, such as in Acacia sphaerocephala, to the more complex tunnel networks found in the tuber of the Myrmecodia. Now here’s a superb example of a refined mutualistic relationship. This plant gains both a defense mechanism and a food source from its association with ants. Myrmecodia are epiphytes (they live on other plants), and are somewhat unusual in appearance, as the bulk of the organism is usually made up of the tuber (some call this the caudex, which is a modified stem). Within this tuber is a network of tunnels, some with smooth walls which the ants live in, and some covered in nodules in which the ants deposit their refuse. This refuse is then used as nutrient by the plant. A variety of ant species have been found living in these plants and in Australia they include Philidris cordatus (most common inhabitant), Pheidole megacephala and Crematogaster physothorax (Huxley, 1978). Even frogs have been found using them as a temporary home!
The fact that organisms from two completely separate kingdoms have managed to co-evolve and work so efficiently together is always pretty neat.
Huxley, Camilla R. 1978. The Ant-Plants Myrmecodia and Hydnophytum (Rubiaceae), and the Relationships between their Morphology, Ant Occupants, Physiology and Ecology. New Phytologist.
As a side note… how’s this for a title!
Amador-Vargas, S. 2008. Spartan defense in the Thermopylae pass: Strategic defense by aggregations of Pseudomyrmex spinicola (Hymenoptera, Formicidae) on the trunk of Acacia collinsii (Mimosaceae). Insectes Sociaux 55 (3):241-245.