Termites may be fond of eating wood. However, they are incapable of digesting the wood that they eat. The one responsible of digesting all the wood ingested by the termites are the protists that live inside their bodies. The reason why the relationship is mutualistic is that both organisms coexist harmoniously by benefiting each other in a metabolic level. Termites, while they eat wood are intolerant to the cellulose content of that they eat. Cellulose is a plant's (or in this case, wood) enveloping membrane. As they cannot munch their way to their intake's absolute ingestion, the protists, which likes all the cellulose membranes of the woods does the job for the termites. After the wood's cellulose is metabolized by the protists, the nutrients of the metabolized wood are then excreted to the termite's benefit and thus the mutualistic relationship between two organisms.
There are only a few living organisms on earth that thrive into existence with this kind of relationship which is utterly more than just a metaphoric symbiotic mutualism. The only sad thing about termites is that the general understanding of them is related to pests. When we talk about termites, we often relate ourselves with property destruction which is definitely a bad thing to any home owner. However, that's just true in some parts as there is only 5% of the overall species of termites that are considered pests and should be appropriately feared by any home owner. The rest of the species are natural habitat dwellers that are surreally found anywhere near a human residential area.
To some termites are even considered to be a blessing, especially with farmers. Farmers in some parts of the world have developed methods on how to cultivate and control the propagation of termites in their farms. This is because termites have the natural ability to aerate soil, breakdown organic matter which could later on turn into humus, a compose that could nurture the soil, improve soil fertility and could even provide a source of protein to some organisms that inhabit a farm. Not to mention the definite role it serves in the ecology's web of life.
Here's a question to Ponder:
Q: Now that you know that there is mutually symbiotic relationship between the protists and termites and that you know they need each other to live. The question now is which one of them evolved first?
A: That is indeed quite in an interesting question. Granting that there is a symbiotic relationship, and that the mutualism between two organisms is so tight that it can become fatal for each one of them when separation occurs, there is then a gap in between the evolutionary understanding of these two organisms that needs filling; which could have come first when one could have died without the other?
The answer is that they have coevolved in time. Meaning, they have invariably evolved simultaneously, that neither one of them are left alone to exist ahead of time before the other. They're predecessors may have been able to exist before them though.
The protists inside a termite's body that breaks down all the wood's cellulose are flagellates that belong to certain genera - the genera Trichonympha and Personympha. These flagellates ancient lineages have evolved and existed long before any insects have inhabited earth. But protists species themselves have not evolved before the termites did. They have in fact evolved simultaneously, or "coevolved".
It's greatly possible that the ancestors of termites didn't just eat woods in their era. Just like any other insects of time that belonged to the same genera, before and present, they thrived as herbivores and would invariably eat edible plant parts. There might be times they eat wood but that is just probably in passing and not on a focus diet basis.
At some point the termite-like ancestors have ingested the protists along, probably upon consumption of their plant material diet considering that these protists also do feed on plant materials. If at some point some of the protists were found inclusively dieting on wood, over time they would have also paved the evolution of enzymes that could break down wood cellulose. It is then highly probable that the ancestral pre-termite insects have ingested them as well as they sparingly forage indiscriminately at times.
Protists are naturally symbiotic organisms; therefore it should not be a surprise that they could reside inside a larger organism's system. The type of relationship between the host and the protists could be classified into three. The relationship can be commensal, wherein the resident protists benefit themselves without putting the host in danger. It can also be parasitic, wherein they gain benefit in return harming the host's wellbeing. And lastly, mutualistic, where both parties benefit from each other and thus they coexist in a constant cycle of benefaction. The kind of relationship that would come out is contingent to the natural genetic developments that will transpire from one generation to another in the two organisms.
At present, termites have fostered the residence of protists inside their digestive tract without harming their system. When the protists have thrived in the termite's gut unharmed, it should be that the protists have provided metabolic incentives for their hosts, enabling them to gain natural leverage over the other termite ancestors that have not ingested the protists. The ancestral termite-like hosts should have gained an energy advantage which would likely have enabled them also to procreate more and thus leaving stronger genes to replicate in the following generations.
The present termites have the characteristic to pass on their own gut flora to their larva in an early stage. This is by transmitting their saliva that contains the protists, orally to their offspring. This genetically controlled trait of termites is also crucial in the concurrent evolution of both the flagellate and termite.
And in a full evolutionary cycle, that once optional feeding of wood became the termite's primary source of diet as they become naturally selective to focus on that specific food source and thus, tied the mutualism between the symbiotic organisms.
Michael Rozatoru :)